US3848187A - Method of detecting the onset of formation of adherent precipitates on surfaces immersed in liquids, and of controlling the formation of such precipitates - Google Patents

Method of detecting the onset of formation of adherent precipitates on surfaces immersed in liquids, and of controlling the formation of such precipitates Download PDF

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US3848187A
US3848187A US00335676A US33567673A US3848187A US 3848187 A US3848187 A US 3848187A US 00335676 A US00335676 A US 00335676A US 33567673 A US33567673 A US 33567673A US 3848187 A US3848187 A US 3848187A
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Prior art keywords
test surface
liquid
adherent
contact resistance
scale
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G Rohrback
E Holmes
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ROHRBACK Corp A WASHINGTON CORP
Magna Corp
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Magna Corp
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Priority to DE2407081A priority patent/DE2407081C3/de
Priority to GB725074A priority patent/GB1433962A/en
Priority to IT48697/74A priority patent/IT1015819B/it
Priority to JP49022013A priority patent/JPS5025261A/ja
Priority to FR7406474A priority patent/FR2219413B1/fr
Priority to US05/509,328 priority patent/US3951161A/en
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Assigned to ROHRBACK TECHNOLOGY CORPORATION A CORP OF WASHINGTON reassignment ROHRBACK TECHNOLOGY CORPORATION A CORP OF WASHINGTON ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ROHRBACK CORPORATION A CORP. OF CA.
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T137/00—Fluid handling
    • Y10T137/2496—Self-proportioning or correlating systems
    • Y10T137/2499—Mixture condition maintaining or sensing

Definitions

  • the field of the invention is the detection and control of the formation of adherent precipitates (such as scale, paraffin wax, etc.) on various surfaces.
  • adherent inorganic scale is the most common form of harmful precipitate
  • adherent organic deposits are also major problems in certain industries.
  • the formation of harmful precipitates is not confined to aqueous systems.
  • sticky adherent deposits form on metal surfaces of the reactors, heat exchangers, or transfer lines. These deposits are often the result of heating of the oil being processed, which heating changes or decomposes asphaltic constitutents, asphaltenes or similar substances to form undesired adherent coatings.
  • cooling instead of heating is the cause of the problem.
  • crude petroleum oil will deposit adherent coatings of paraffin wax when the temperature of the oil or of the surfaces over which it passes, is lowered sufficiently.
  • Scale or deposit formation is also a troublesome occurrence in many systems containing organic liquids. For example, deposits frequently occur in high wattage electrical transformers in which the windings are immersed in hydrocarbons or in halogenated aromatic compounds and the like; in hydraulic oil systems containing polyols, ethers and other organics; in heattransfer liquid systems such as heavy oil, bisphenol A or similar highboiling organics; and in numerous organic chemical processing units.
  • Scale and other harmful coatings are likewise found in two-phase systems. For example, in the processing of form, and of determining the conditions under which such formation can be prevented either by addition of chemical scale inhibitors or by control of process variables. It is highly important that the method be capable of implementation by commercial instruments, which function at all times and which do not require trained chemists or scientists for their operation. It is also extremely important that the method be so sensitive that the tendency of a system to develop scale will be detected without waiting until such formation has created substantial harm in the commercial system being monitored.
  • test solutions are prepared which are basically unstable and will, in response to heating freshly produced crude oil, the fluid is heated in a (or standing) and to the passage of time, yield precipitates of alkaline earth metal carbonates or sulfates.
  • Different chemicals are added to such test solutions, and the degree to which such additives prevent or inhibit precipitation is determined. It is, however, emphasized that such tests do not provide continuous monitoring of an actual commercial system. nor do they necessarily produce significant data relative to formation of adherent scale in the actual system. It is to be noted that adherent scale or other precipitate is extremely harmful, but that those precipitates which are not adherent may be relatively harmless.
  • Stability is ascertained by measuring or calculating fro'm composition analysis, the minimum amount of acid or base required to effect precipitation.
  • the amount of reagent tolerated by the solution without precipitation is taken as being proportional to stability and thus as being inversely proportional to the scale-forming tendency of the liquid.
  • Such periodic tests can, at best, only be indirectly and uncertainly related to the tendency of an actual system to form adherent scale (or other) deposits.
  • the method comprises measuring the electrical contact resistance between a test surface and an auxiliary contact surface while such surfaces are immersed in the liquid from which precipitation occurs.
  • the surfaces should not be maintained in continuous engagement at the same point, being instead intermittently pressed together or rolled together in such manner as to permit scale buildup and to prevent scraping-off, penetration, or other destruction or disturbance of the nuclei of incipient scale (or other adherent precipitate).
  • the electronic conduction circuit is broken.
  • the liquid is a good electrical conductor (as defined below)
  • a surprisingly high contact resistance is detectable and indicates the onset of scale or other precipitate. If the liquid is not an electrical conductor, but is instead an insulator, the increase in contact resistance is even greater and is readily ascertained.
  • the method of the invention further relates to numerous additional matters, including (among others) (I) the selection of materials and polarities in order to achieve high sensitivity and other important beneficial results, (2) the use of an auxiliary electrode, and (3) the cleaning of the test surface either after each test or after a plurality of sequentially performed tests.
  • the method additionally relates to controlling the temperature and chemical properties (such as pH) at the test surface, and the rate of impingement of liquid against the test surface.
  • the method relates to auto matically applying heat flux.
  • cathodic current density, etc. to a test surface in proportion to the difference between an empirically established set point" surface resistance and the actual contact resistance at the test surface, in order that the heat flux, etc., will asymptotically approach the maximum value at which adherent scale or other precipitate will not deposit.
  • Such maximum value is then employed as the index" of the liquid, and is highly useful relative to the steps which must be taken in order to prevent formation of adherent deposits.
  • the method of the invention is related to an actual industrial system in a plurality of ways. among which are the following:
  • FIG. I is a schematic representation of a simple form of apparatus for use in performing the method of the invention.
  • FIG. 2 is a schematic representation of a form of an paratus wherein the contacting is of a rolling type
  • FIG. 3 illustrates a form of apparatus wherein the rolling contact is effected by means of spheres
  • FIG. 4 corresponds to the lower portion of FIG. 3,
  • FIG. 5 shows schematically an apparatus wherein the contacting is by pivotal movement, and also shows a means for effecting heating of the test surface;
  • FIGS. 6 illustrates an apparatus wherein the heated element is cylindrical and is motor driven
  • FIG. 7 illustrates schematically a different form of heating, in that the heat is caused to flow radially inwardly instead of radially outwardly;
  • FIG. 8 illustrates an apparatus in which the test sur face is a continuously moving disposable tape, and in which such tape is heated by passage of electric current therethrough;
  • FIG. 9 is a schematic representation of an apparatus in which the test surface is caused to be cathodic, relative to an auxiliary electrode, in order to increase the rate of scale deposition on some test surfaces;
  • FIG. 10 represents schematically a form of apparatus in .which means are provided to impinge a jet of liquid against the test surface, to thus increase the rate of scale deposition;
  • FIG. 11 is a schematic representation of an additional embodiment, in which both the test surface and the DEFINITIONS Throughout this specification and claims, the words precipitate, etc., are not employed only in the strict chemical, conventional sense. Instead, they denote any condition whereby, for any reason, a coating deposits out of a liquid and onto a surface immersed in such liquid. The deposition of the coating may result from one or more of numerous factors, including chemical breakdown, heating, cooling, change in pH, aggregation and adhesion of suspended particles, etc.
  • conductive liquid, electrically conductive liquid, etc. are restricted, in the present specification and claims, to those which are ionic conductors of electricity. These are to be distinguished from those liquids, such as mercury, which are good electronic conductors of electricity. They are also to be distinguished from liquids, such as oil, which are either insulators (nonconductors) or are very poor conductors of electricity.
  • overvoltage is employed, in the present specification and claims, to denote that voltage drop, across the contacting surfaces, which is in excess of what would be expected from Ohms law (that is to say, from the application of Ohms law to determine voltage by multiplying current times the resistance of the liquid).
  • Ohms law that is to say, from the application of Ohms law to determine voltage by multiplying current times the resistance of the liquid.
  • a container contain ing a liquid 11 which will, under certain conditions, precipitate (as that term is defined above) adherent scale or other undesired adherent coating onto a test surface which is immersed in the liquid 11.
  • Container 10 may be part of, or in communication with, an industrial system (containg, for example, a heat exchanger) wherein scaling or fouling of immersed surfaces is a major problem.
  • container 10 may be employed in the laboratory.
  • test surface 12 in FIG. 1 is at a right angle to the plane of the drawing, being one face ofa cube l3. Normally, the temperature of the cube l3, and thus of test surface 12, is caused to be substantially greater than that of the liquid.
  • the cube 13, and various other elements represented in the present drawings, are supported by suitable means, not shown.
  • auxiliary contact (or contactor) element 14 adapted to be moved into electrical contact with the surface 12.
  • contact element 14 is mounted on a connector bar 16 one portion of which slides in bearings 17 which are mounted on a support 18.
  • a suitable actuating means 19 is connected to bar 16 in order to effect intermittent engagement of the contact element 14 with test surface 12.
  • auxiliary contact element 14 be brought into engagement with test surface 12in such manner that there will be no substantial sliding, scraping, rubbing or other undesired movement which would tend to remove from surface 12 the nuclei of incipient scale, etc.
  • the arrangement is caused to be such that the element 14 moves perpendicularly to surface 12.
  • the surface of element 14 adjacent surface 12 is made spherical, as indicated at 21.
  • the actuating means 19 is caused to effect relatively slow travel of contact element 14 towards surface 12, and to effect engagement at a relatively low force.
  • the contact force is, typically, in the range of about an ounce to two up to a few pounds, depending on various factors such as (for example) the shapes and sizes of the contacting surfaces.
  • the pressure is so adjusted that there will be a relatively low voltage drop present between surfaces 12 and 21 before any scale deposition has occurred, but a relatively high voltage drop therebetween (as discussed below) after scale nuclei have formed on the test surface.
  • a suitable voltage (and current) source 22 is provided.
  • One terminal of source 22 is connected through a lead 23 to cube 13, whereas the other source terminal is connected through a resistor 24 and a switch 25 to connector bar 16 (which is electrically conductive).
  • the source 22 should be a DC source in order to maximize sensitivity as discussed hereinafter.
  • the resistor 24 is suitably adjusted to prevent excessive current flow, and to correlate the current flow in the circuit with the scale of a voltmeter 26 which is bridged between cube 13 and contact element 14.
  • the voltmeter is of a suitable high-resistance type, and may be calibrated in terms of ohms, if desired.
  • the actuating means 19 is first operated, to engage surfaces 12 and 21 witheaeh other, after the cube 13 has been in liquid 11 only a very short period of time insufficient to effect precipitation of a coating of scale or other undesired material.
  • the reading of voltmeter 26 is then noted, after closing of switch 25, and this is the E reading on a clean surface.
  • l3. may be taken as the average of an arbitrary number of readings taken at different spots on the test surface while maintaining the system variables essentially unchanged.
  • the E reading is desirably caused to be the one which results when there is electronic conduction betweenthe test surface and the contactor 14.
  • Actuating means 19 is then operated to retract the auxiliary contactor 14 from test surface 12, following which a considerable period of time is allowed to pass.
  • the contact element 14 is then re-engaged with surface 12, and again at periodic intervals, until the reading of meter 26 is far above the E reading.
  • the jump in the reading of meter 26 indicates the presence of deposited scale or other precipitate on the test surface 12 at whatever region of the test surface is then engaged by the leftmost portion (FIG. 1) of spherical contactor surface 21.
  • liquid 1 1 which is an insulator or a very poor electrical conductor, for example, products (petroleum and liquid products of petroleum) being processed in a refinery
  • the increase in the reading of meter 26 will be very large since there will actually be insulating material present between all portions of surfaces 12 and 21.
  • insulating material is the oil itself secondarily, the insulating material is the adherent precipitate on surface 12.
  • That the meter 26 will exhibit a greatly increased reading even when the liquid 11 is highly conductive, and even when surfaces 12 and 21 are spaced from each other only by a very thin and small nucleus of scale or the like, is a surprising phenomenon.
  • particularly high readings greater sensitivity
  • the overvoltage is the result of a shifting from electronic conduction between engaged surfaces 12 and 21 to ionic conduction (through the liquid 11) between the surfaces which are spaced a slight distance from each other.
  • ionic conduction there must be chemical reactions accompanied by ionization and the liberation of gas, and these chemical reactions require electrical energy which is indicated by a surprisingly high reading on voltmeter 26.
  • the meter 26 will detect scale or other adherent precipitate long before there is any visible indication of scale on surface 12, and tong before there is any change in the heat transfer rate between surface 12 and the surrounding liquid.
  • source 22 is a DC source, which is the preferred case as sbove noted. If source 22 were not a DC source, there would be no polarization (with consequent chemical reactions and resulting surprisingly high reading on meter 26). If source 22 were an AC source, such as a conventional -cycle AC source, then the contact" resistance would increase but not nearly so greatly as is the case when the source is a DC source.
  • wet scale is normally not regarded as a good electrical insulator. Nevertheless, the presence of such wet scale between the surfaces 12 and 21, to provide a spacing therebetwecn so that conduction is no longer electronic, causes the conduction instead to be ionic and (when the voltage source is DC) creates the overvoltage necessary for the big resistance jump which is indicated by the surprisingly high reading of meter 26.
  • the current flow between surfaces 12 and 21 is caused to be in the range between l microamp and 10 milliamps. It is preferred not to use large currents, since these could affect the scale deposits and could create undesired corrosive effects. Even those low currents produce the above-noted surprisingly high voltage drop between surfaces 12 and 21, due to the overvoltage effect when liquid 12 is an electrical conductor, and due to the insulating effect of the liquid when it is an insulator.
  • the liquid 11 is seawater, and that the contact region is caused (by the interposition of scale or other substance) to be open approximately 0.01 centimeter.
  • the area ofcontact is 0.1 square centimeter. Since the resistivity of seawater is 30 ohmcentimeters, the expected resistance of the indicated seawater region is 30 times 0.01 divided by (it, or 3 ohms. Despite this low calculated resistance value, the present method causes the actual resistance to be very much higher, for example in a range of 30 ohms to many thousands of ohms. This greatly increased ohm value results, it is believed, primarily from the overvoltage effect described above. Because of this high value, even the preferred low currents may cause a relatively large and readily detectable voltage drop across the supposedly 3-ohm gap.
  • the presence of incipient scaling on test surface 12 is an indication of the presence of incipient scaling on portions of the industrial system. This is particularly true when, as described below, the heat flux and other conditions at surface 12 are correlated to those present in the industrial system. Therefore, as soon as scaling is noted, a suitable change is made in order to prevent continuance of substantial precipitation of adherent scale or other undesired substance.
  • This change frequently comprises, for example, the addition of scale-inhibiting compounds (such as sodium hexametaphosphate or an organic phosphonate when the liquid is aqueous, and such as sulfonic acid, naphthenic acid or an oil-soluble detergent-type substance when the liquid is petroleum or a petroleum product) to the liquid 11.
  • scale-inhibiting compounds such as sodium hexametaphosphate or an organic phosphonate when the liquid is aqueous, and such as sulfonic acid, naphthenic acid or an oil-soluble detergent-type substance when the liquid is petroleum or a petroleum product.
  • test surface 12 is either cleaned, or a new E reading of meter 26 is noted, as described below under the heading Cleaning of the Test Surfaces.
  • the contacting elements namely, the test surface and the auxiliary electrode
  • the cube 13 may be moved upwardly, downwardly or laterally, between operations of the actuating means 19. Since the scale only precipitates at spaced regions, during the early stages of formation, this relative movement of the cube 13 will create a condition whereby some engagements of surface 21 with surface 12 will create a high reading on meter 26, whereas other engagements will not (depending on whether or not scale nuclei are interposed between the surfaces).
  • the voltage-peak reading which results from presence of scale exactly at the region between the test surfaces
  • the average reading of meter 26 is of impor tance. It is also possible to average the voltage-peak readings.
  • the present method including those portions of the method described above as well as those portions described below, it is possible to determine rapidly whether or not scale is forming in the system at a significant rate.
  • the present method may be used to determine within minutes or hours (whereas various prior-art workers waited days, weeks, or even months) whether or not significant scaling is occurring.
  • the present method is extremely convenient and is susceptible to automatic instrumentation.
  • the materials employed to form the test surface, and the surface of the contact element which engages the test surface are of major importance. There are practical limitations relative to these materials, one being that both must be electrical conductors. Although, for reasons stated hereafter, it is normally important that the surfaces be formed of materials which arev resistant to corrosive attack by the liquid 1 1, there may be exceptions, as when corrosion products are an important part of the adherent deposits under'investigation (for example, in the detection of an adherent deposit that is partially an insoluble precipitate from the liquid, and partially a corrosion residue of a metal surface). Other exceptions may occur when it is determined to be desirable that the material forming the test surface be the same as a material employed in an industrial system being monitored.
  • the materials should be such that they are able to withstand substantial numbers of cleaning steps without the necessity of frequently replacing either the test surface or the auxiliary contact element.
  • the materials used to form the test surface and the auxiliary contactor surface be such as will produce high overvoltages.
  • the materials be such that there is a very high resistance present at the inter' face between each surface and the conductive liquid in engagement therewith.
  • Such high'interface resistance is synonymous with a substantial absence of a tendency toward corrosion.
  • the materials be such that they will not corrode in the liquid 11 under consideration.
  • Such lack of corrosion not only greatly increases the useful life of the surfaces but also (in conductive liquids) creates the desired high interface resistance with consequent pronounced overvoltage effect, thus producing high resistance readings in response to only a small amount of scaling.
  • test surface and the auxiliary contacting surface examples include carbon, graphite, stainless steel, nickel alloys (such as, for example, Inconel), palladium, and platinum.
  • nickel alloys such as, for example, Inconel
  • palladium examples of satisfactory materials for the test surface and the auxiliary contacting surface are carbon, graphite, stainless steel, nickel alloys (such as, for example, Inconel), palladium, and platinum.
  • the platinum or palladium may be coated on a titanium or other less expensive substrate.
  • Mercury may also be employed to form the contacting surface.
  • the material forming the test surface may be different from that forming the contactor surface (such as 21).
  • the test surface 12 may be formed of platinum whereas the contactor surface 21 may be formed of carbon, the liquid 11 being aqueous. Because of the low cathode overvoltage of platinum, it is caused to be an anode. In the exemplary platinum-carbon instrument, when the electronic conduction is broken by an adherent scale deposit, leaving only the ionic conduction path between the surfaces, the oxygen overvoltage at the platinum surface and the hydrogen overvoltage at the carbon surface provide an effectively higher resistance and thus higher instrument sensitivity.
  • test surface should be made of the same material as a certain part of an industrial system.
  • the test surface may be made of copper to correspond to the copper tubes of a heat exchanger. It is then usually preferred to cause the test surface to be a cathode, because even corrodible metals have relatively high overvoltages when they are made cathodic.
  • a metal plate 27 is fixedly mounted over the container (not shown) of liquid, and has rotatably mounted therein (by means of a suitable electrically conductive bearing) a vertical cylinder 28 which forms the test surface 12a.
  • a motor 29 effects rotation of cylinder 28 about a vertical axis, at a desired slow speed.
  • An electrically conductive vertical shaft 31 is mounted in plate 27 by means of an insulating (and somewhat resilient) mounting 32, in a nonrotatable relationship.
  • Rotatably mounted at the lower end of shaft 31 is an electrically conductive auxiliary contactor wheel 33 having rhe auxiliary contactor surface 21a thereon. (Alternatively, wheel 33 may be fixed to shaft 31, and the shaft caused to rotate in an insulating bearing.)
  • FIG. 2 thus illustrates an embodiment wherein the contact is rolling, as distinguished from the intermittent opening and closing described relative to FIG. 1. It is to be understood that the rate of rotation of shaft 28 is very slow, being typically on the order of about four revolutions per hour, so that scale nuclei will be able to build up on test surface 12a without being disturbed by the auxiliary contactor surface 21a. Alternatively, instead of having continuous slow rotation, there may be less slow rotation but performed only intermittently.
  • a vertical electrically conductive cylinder 34 is driven by a motor 36 and there' fore rotates about a vertical axis.
  • the external surface of cylinder 34 constitutes test surface 12b.
  • the auxiliary contactor surfaces 21b are formed on electrically conductive spheres which seat on a downwardly convergent frustoconical race surface 37.
  • Surface 37 is provided on the interior of an electrically conductive race 38 which is fixedly mounted in immersed relationship in the liquid.
  • FIG. 3 The electric circuit in FIG. 3 is identical to that in FIGS. 1 and 2, except that conduction to cylinder 34 is through a slip ring 39 which is fixedly mounted (to a suitable support, not shown) around the cylinder and in which the cylinder rotates.
  • motor 36 drives cylinder 34 at a slow rate or intermittently, permitting scale to build up on the test surface 12b.
  • the embodiment is identical to that of FIG. 3 except that the cylinder 34 has a flange 41 fixedly mounted thereon, the outer surface of the flange being downwardly convergent and frustoconical and forming the test surface 12c. Furthermore, the aux iliary contactor surfaces 210 are provided on the exteriors of downwardly tapered, electrically conductive roller bearings which are seated between test surface 12c and interior race surface 37a of race 38a.
  • the embodiment of FIG. 4 is identical to that of FIG. 3, except that the roller bearing elements are not spheres but are instead elongated elements having somewhat frusto conical exterior surfaces
  • an insulating disk 43 has extended therethrough two electrically conductive mounting rods 44 and 45.
  • a test cylinder 46 is mounted in the lower ends of rods 44 and 45, in horizontal relationship, the external cylindrical surface of the cylinder 46 being the test surface 12d.
  • An electrically conduc tive contactor rod 47 is pivotally mounted in an oversize opening in disk 43, by means of a rubber grommet or O-ring 48.
  • Rod 47 is cylindrical, and has a cylindrical exterior surface constituting the contactor surface 21d. In its normal or free position, rod 47 does not engage cylinder 46.
  • the contactor rod 47 may be manually or automatically pivoted in such manner as to cause surfaces 12d and 21d to be in engagement, such pivoting being permitted by the resilient grommet 48.
  • FIG. Sis one wherein the contact motion is not rolling, not is it directly perpendicular as is the case relative to the embodiment of FIG. 1, being instead pivotal.
  • the contact resistance between surfaces 12d and 21d is read by an ohmmeter 49 which is connected in circuit between contactor rod 47 and mounting rod 45.
  • Ohmmeter 49 may be of conventional construction, and contains its own source of DC power. It is to be understood that, instead of using the ohmmeter 49, the electric circuitry of FIG. 1 may be employed to measure the contact resistance between surfaces 12d and 21d.
  • an insulating plate 51 has rotatably mounted therein a hollow, vertical, electrically conductive cylinder 52.
  • a flange 53 At the lower, immersed end of cylinder 52 is a flange 53 the external surface of which is cylindrical and constitutes the test surface 12e.
  • An electrically conductive shaft 54 is fixedly mounted in vertical relationship in plate 51, and has an electrically conductive wheel 55 rotatably mounted (by an electrically conductive bearing) at the lower end thereof.
  • the external cylindrical surface of wheel 55 is the auxiliary contactor surface 2le, and is in rolling contact with test surface 122. Therefore, when cylinder 52 is slowly (or intermittently) rotated by means of a suitable motor 56, the friction between surfaces 12e and 2le effects rotation of wheel 55 as previously stated relative to the embodiment of FIG. 2.
  • the ohmmeter 49 is bridged between shaft 54 and a slip ring 57 on cylinder 52.
  • slip ring, and all slip rings described in the present application are similar to the one 39 described above relative to FIG. 3.
  • a hollow, electrically conductive cylinder 58 is mounted in vertical relationship in the liquid, having an internal flange 59 the upper-inner surface of which is frustoconical and down wardly convergent. Such surface constitutes the test surface 12f.
  • Several electrically conductive spheres are mounted on the test surface 12]", and their spherical surfaces constitute the contactor surfaces 21f. At their inner portions, the spheres seat on the downwardly convergent frustoconical surface of a wheel 61 which is fixedly mounted at the lower end of the vertical shaft 62 driven by a motor 63 (both the wheel and the shaft being electrically conductive).
  • motor 63 When motor 63 is energized, itrotates shaft 62 and thus wheel 61, causing the wheel to drive the spheres around the test surface 12f. As in all embodiments of the invention, the motor is operated sufficiently slowly, during a test, to prevent any disturbance with the growth of scale or other precipitate.
  • the contact resistance between surfaces 12f and 21 f is read by ohmmeter 49, which is connected between cylinder 58 and a slip ring 64 on shaft 62.
  • a tank 66 containing the liquid 11 is adapted to receive a flexible, disposable test strip 67.
  • Strip 67 is mounted on a supply roll 68 which is suitably supported in rotatable relationship above one end of the tank.
  • the test strip is pulled from roll 68, and through th liquid in tank 11, by means of a suitable drive means represented scehmatically at 69.
  • Both the upper and lower surfaces of the strip 67 constitute the test surfaces 12g. Both of these test surfaces are contacted by the auxiliary contactor surfaces 21g which are provided, respectively, on upper and lower electrically conductive rolls 71 and 72. Such rolls are rotatably mounted in the tank, on suitable shaft and bearing means which are electrically conductive.
  • the ohmmeter 49 is connected to the shaft and bearing means for the respective rolls 71, 72, and is thus connected to the contactor surfaces 21g. It therefore reads the contact resistances between each of surfaces 21g and each of surfaces 12g. There are, accordingly, two sets of contact surfaces, these being in seriescircuit relationship.
  • alkaline earth metal carbonates are far less soluble than the bicarbonates, carbonate precipitates will form when the solution is heated. If such heat is applied by means of hot surfaces in contact with the bicarbonate-containing solution, the precipitate will form at the heated surfaces and adherent scale will result.
  • the deposits are, for example, and as previously noted, formed of such things as the products of decomposition of asphaltenes, etc.
  • One such way of performing the present method is to determine the critical heat flux (or temperature), at the test surface, at which scale, etc., first starts to form at a significant rate. This is done by gradually increasing (or reducing) the heat flux, and then noting the critical value at which scale, etc., forms. When the test surface is hotter than the liquid, such critical heat flux is represented by the lowest value at which scale forms at a significant rate. When the test surface is at a lower temperature than that of the liquid, the critical heat flux is the highest value at which scale starts to form at a significant rate. During the tests, other factors (such as liquid impingement velocity) are preferably held con stant.
  • the critical heat flux thus determined may be referred to, for convenience, as the scale index" of the particular liquid.
  • scale index is correlated, by empirical data, to the scale-forming tendency of the particular liquid under consideration.
  • suitable steps are taken (in an associated industrial system containing the same liquid) in order to prevent significant scaling. For example, scale inhibitors are added to the liquid, or suitable process changes are made.
  • the method may also be performed by effecting simultaneous testing relative to several test surfaces, each at a different, known, heat flux value.
  • the scale index is the heat flux value at whichever test surface shows significant scaling while those cooler do not. Stated otherwise, when the liquid is such that scaling results from heating, the lowest-temperature surface which shows significant scaling determines the scale index.
  • Another of the ways of practicing the present method is to cause the heat flux at the test surface to be substantially the same as that at critical components of an industrial system being monitored.
  • the heat flux at a hot test surface may be caused to correspond to the heat flux at the tubes of a heat exchanger. Then, if significant scale starts to form on the test surface, at the specified heat flux, it is known that scale inhibitor should be added (or process changes made) in order to prevent significant scaling of the heat exchanger tubes.
  • the determination of scaling is achieved long before any harmful changes, such as alterations in the heat transfer rate, are caused to result.
  • the input terminals of a variable transformer 75 are connected through a switch 76 to a suitable AC source, uch as a l volt 60-cycle AC source.
  • the output terminals of transformer 75 are connected, respectively, to the mounting rods 44 and 45. Heating current is therefore passed through the test cylinder 46 and causes it to become heated to a degree determined by such factors as the setting of the transformer, the composition of the test cylinder 46, etc.
  • the test cylinder may be formed of carbon.
  • switch 76 Before making each reading of contact resistance, switch 76 is opened in order to prevent the heating current from affecting the reading of ohmmeter 49.
  • ohmmeter is connected directly to the contactor rod 47, and is connected to mounting rod 45 through part of the output winding of transformer 75.
  • heating of the test surface 122 is effected by introducing a suitable heating coil 77 into the hollow cylinder 52.
  • the terminals of the coil are connected through slip rings 78 and 79 to a power source 80.
  • Such source 80 which may, for example, be
  • transformer is adapted to supply a variable amount of heating power to the coil.
  • a variable power source 81 is connected through leads 82 and 83 to diametrically opposite portions of a heating element 84 which is mounted around the cylinder 58 radially outwardly of surface 12f.
  • Heating element 84 may be formed. for example, of a high-resistance metal.
  • a heattransmissive electrically insulating layer 86 (shown in exaggerated thickness) is interposed between ring 84 and the external surface of the cylinder 58.
  • switches 76 are provided in the power circuits in the embodiments of FIGS. 6 and 7, these switches preferably being opened before each reading of the contact resistance.
  • first and second sets 87 and 88 of contactor rolls are engaged with the test strip 67. on opposite sides of rolls 71-72, for the purpose of passing heating current through the strip.
  • the rolls 87 on the left side of rolls 7172 are provided with sharp protuberances 89 in order to penetrate scale and thus minimize contact resistance.
  • a suitable AC source such as a NO volt. btl-cycle source, is connected through a switch 76 and the variable transformer 75 to rolls 87 and 88, so that the sec ondary circuit of the transformer 75 includes such rolls and also the portion of test strip 67 therebetween. As described above, switch 76 is opened prior to each reading of ohmmeter 49.
  • the heating coil 77 of the embodiment of FIG. 6 may be replaced by a correspondingly shaped cooling tube adapted to conduct chilled brine through the cylinder 52.
  • the slip rings 79 and 78 are replaced by brine-transfer rings (and suitable seals) which are respectively in communication with opposite ends of the brine tube in the cylinder 52.
  • the power source is replaced by a refrigeration system which supplies cold brine through pipes to the respective brine transfer rings 78 and 79.
  • Such refrigeration system is adapted to supply the cold brine to one of the brine transfer rings and thus to one end of the brine tube.
  • the other end of the brine tube connects back to the refrigeration system, the brine being continuously cooled by the refrigeration system and circulated through the brine tube to thereby continuously cool test surface 12e.
  • Means are provided to vary the brine flow (or temperature) and thus control the tempera ture of the test surface.
  • pH margin is the difference between the pH of the system liquid and thehigher pH value (present in the test tank liquid) at which adherent scale deposits start to occur at a significant rate.
  • the same test may be performed relative to a system where adherent deposits result from a decrease in pH, the pH at the test surface then being progressively decreased instead of increased. 8
  • the alteration of pH of the solution flowing past the test surface may, for example, be accomplished by addition of a base or acid of known concentration and at a known rate. pH measuring instruments are readily available to determine the pl-Iof the solution, and to regulate the addition of base or acid in order to maintain the solution at the desired pH in the region of the test surface.
  • An additional method of changing the pH of an aqueous solution at the test surface is by electrolysis of water, with inert electrodes. Liberation of hydrogen at a cathode surface causes a localized pH increase, and of oxygen at an anode surface causes a localized pI-I decrease, in accordance with the following equations:
  • pH is but one of the chemical properties of the liquid.
  • Other chemical properties may also be controlled in order to change the scaling tendencies of the particular liquid under consideration.
  • test surface is caused to be cathodic relative to the auxiliary electrode immersed in the liquid 11, and sufficient current is applied that scaling will result at the test surface.
  • the current causes the liquid at the test surface to be more basic, in accordance with Equation (6) above, and this results in the scaling (it being assumed that the solution is one which precipitates scale when it becomes sufficiently basic).
  • the magnitude (current density) of the current flowing through the liquid from an auxiliary electrode (anode) to the cathodic test surface is gradually increased, and the current density which first produces significant scaling on the test surface is employed as an indication of the scale-forming tendency (the scale index) of the liquid in which the test surface is immersed.
  • other factors such as heat flux, liquid impingement velocity against the test surface, etc. are preferably maintained constant.
  • an auxiliary anode electrode 91 is connected to the positive terminal of a DC source 92.
  • the electrode 91 is immersed in the liquid 11 which is con tained in a tank 93.
  • An electrically conductive cylinder 94 is also immersed in liquid 11, and has the test surface 12h thereon.
  • the cylinder is driven by a motor 96 in order to change the region thereof which is contacted by an apparatus corresponding to that described relative to FIG. 1.
  • Cylinder 94 is connected to the negative terminal of DC source 92, and thus becomes the cathode, so that conduction is effected through the liquid 11 (which is an electrically conductive liquid of a type which precipitates scale in response to a pH increase).
  • the liquid at the interface with test surface 12h becomes relatively basic, in accordance with Equation (6) above, to thereby increase the rate of formation of adherent scale on the surface 12h.
  • the magnitude of current flow through the liquid is gradually increased, and an ammeter 95 is employed to note the current level at which significant scaling (evidenced by increased contact resistance) first results.
  • the current level is divided by the immersed area of surface 12h to obtain the current density.
  • Such current density is an index of the scale-forming tendency of the liquid. It may be correlated (by empirical data) to the scaleforming tendencies of the liquid in an associated industrial system.
  • a slip ring 97 is empoyed to connect the resistance-measuring circuit to cylincer 94, whereas a slip ring 98 is employed to connect such cylinder 94 to the negative terminal of source 92.
  • a switch may be provided in series with ammeter 95, in order to open the electrolysis circuit during periods when surfaces 12h and 21 are brought into contact (and switch 29 is closed) to thus determine whether or not scale is forming.
  • a plurality of factors may be varied simultaneously, while other factors are held constant.
  • the auxiliary electrode system may also be utilized to alter chemical properties other than pH in situtations where such alterations are useful in determing scale effects.
  • Equation (7) shows that in aqueous systems oxygen may be generated at the anode. In some cases, oxygen may react with other constituents of the system to form adherent scale. In such instances, by making the test surface anodic the deleterious effects of oxygen inclusion could be studied. In some organic liquids, electrical polarization may cause concentration of specific ions which create deposits and whose harmful effects could be studied similarly.
  • the illustrated apparatus is identical to that shown in FIG. 9, except that the source 92 and the associated anode 91, etc., are omitted. (It is to be understood, however, that the apparatus of FIGS. 9 and 10 may be combined in a single test instrument, and that various others of the apparatus dis- I closed in this application may be combined in a single test instrument.)
  • a variable-speed pump 100 having a suitable speed control (not shown,) is provided.
  • the pump has an intake opening which communicates through a pipe 101 with the lower portion of container 93a.
  • the discharge opening of pump 100 communicates through a pipe 102 with a nozzle 103 which is directed against a portion of test surface 12h at the same ievel as the contactor surface 21.
  • Another manner of performing the method is to cause the velocity of the jet against surface 1211 to correspond to the velocity of liquids at critical portions of the industrial system being monitored. Then, the presence of adherent scale on surface 1212 is an indication that the scale is starting to form at such critical portions of the industrial system, so that corrective measures (such as changes in flow patterns or flow velocities, addition of scale inhibitors. etc.) may be taken.
  • Some embodiments of the method also include the step of cleaning the test surfaces 12, 12a. 12b, etc., either after each test or periodically. Cleaning is effected for numerous reasons, one important one being to maximize sensitivity by starting with an electronic conduc tion path and then shifting (after scale, etc., forms) to an ionic conduction path. Another, and practical, reason for cleaning is to keep the readings from going off range on the associated meter.
  • one device for effecting cleaning of the test surface is a scraper 106, for example, in the nature of a razor blade, which is mounted on a shaft 107 operated by a suitable actuating means 108.
  • a scraper 106 for example, in the nature of a razor blade
  • actuating means 108 When the scraper is shifted against the test surface, and the latter is rotated, most of the scale is scraped off.
  • Another method of effecting substantial cleaning of the test surfaces is to change from low-speed operation of various motors to relatively highspeed operation thereof.
  • various motors 36, 56 and 63 may be shifted to relatively high-speed operation.
  • the high speed operation causes friction and wear between the associated rolling surfaces (such as l2a2la, l2b2lb, 12c-21c, etc.) to rapidly wear away the nuclei of incipient scale.
  • Another method of cleaning is to temporarily lock a bearing, such as the bearing for wheel 33 in FIG. 2.
  • the associated cylinder such as 28
  • the resulting shift from rolling contact to sliding contact rapidly cleans the test surface (such as 12a).
  • An alternative method of effecting test surface cleaning is electrical as distinguished from mechanical. Re ferring to FIG. 9, the polarity of the terminals of DC source 92 may be reversed, making the cylinder 94 an anode as distinguished from a cathode. Such anodic polarity of the cylinder causes the deposited scale to be removed, in many instances, particularly when the volt age applied by source 92 is increased relative to that present during the scaling tests. It has been found that carbonate scale normally dissolves readily, when the test surface is made anodic as distinguished from ca thodic, but that some other types of scale (for example, sulfate) may not dissolve as well.
  • some other types of scale for example, sulfate
  • the materials of which the test surfaces are composed are important relative to the cleaning steps. since the materials should be ones which are not adversely affected to an excessive degree when cleaning takes place.
  • One type of material which works very well with polarity-reversal cleaning is platinum.
  • the test surface is cleaned on each occasion that adherent scale is sensed.
  • This may be controlled either manually or automatically.
  • the actuating means 108 may be automatically interrelated with the scale-sensing circuit, in such manner that a high reading of meter 26 causes the actuating means 108 to shift scraper 106 against the surface 12a, so that such surface is automatically cleaned preparatory to a new scale-sensing test.
  • Suitable timer means are then employed, to effect automatic withdrawal of scraper 106, after an appropriate time has elapsed.
  • the DC source 92 may be automatically interlocked to the scale-sensing circuit in such manner that a relatively high voltage (indicated by a high reading of meter 26) causes polarity reversal at source 92, whereby the surface 12h becomes anodic as distinguished from cathodic. Suitable timing means then are provided to change the surface 12h back to a cathodic state in order to initiate the next scale-sensing test.
  • cleaning may be effected after several tests have been performed but prior to the time that scale builds up to such a degree that the testing is substantially interfered with. It is to be remembered that the present method is capable of detecting scattered nuclei of adherent scale (or other precipitate) on the test surface.
  • one manner of practicing the method is (l) to note when such nuclei first form, (2) then to effect suitable changes in an associated industrial system (relative to addition of scale inhibitors, or changing of process variables) in order to attempt to prevent further preciptation'of scale, (3) then to note a new E on the voltmeter or the associated ohmmeter, and (4 then to determine whether or not additional scale is deposited (such further deposits being indicated by a voltmeter or ohmmeter reading significantly higher than the new E reading).
  • additional scale is normally in the form of new nuclei, so that a greater and greater percentage of the test surface becomes covered with scale. Finally, after a number of such tests have been performed, it is necessary to effect cleaning of the test surface and restart the entire cycle.
  • auxiliary electrode produces two beneficial results, namely, (a) prevention of electrolytic dissolution of the parts by the test current, and (b) rendering negligible the effect of contact resistance at the submerged bearing of the rotating auxiliary contactor. Furthermore, the use of an auxiliary electrode for the purposes specified in the preceding sentence can be combined with the use thereof for the purpose discussed relative to FIG.
  • the illustrated mechanical device is similar to that described relative to FIG. 6, and has been correspondingly numbered, However, in FIG. 11 the horizontal plate 51a is electrically conductive, and shaft 54 is insulated therefrom by an insulating element 109. For purposes of simplicity, the scraper-type cleaning means is not shown in FIG. 11.
  • the ohmmeter 49 is bridged across two submerged contact resistances in series-circuit relationship with each other.
  • One contact resistance is that between surfaces 122 and 21e, which is the critical contact resis tance to be measured.
  • the other contact resistance is that at the bearing between auxiliary contactor wheel 55 and its shaft 54.
  • the last-mentioned contact resistance may, in response to long immersion in the liquid, be subject to scaling and other effects which would increase its contact resistance to a significant extent.
  • an auxiliary electrode 110 is provided and is made anodic relative to the other immersed parts.
  • the auxiliary contactor wheel 55 is then used only as a potential tap, which carries negligible (or no) current.
  • the negligible current (which is not anodic) renders insignificant any increase in the contact resistance between wheel 55 and its shaft 54.
  • the wheel 55, shaft 54, the bearing between wheel 55 and shaft 54, and cylinder 52 are all cathodic relative to the auxiliary anode 110. Accordingly, electrolytic dissolution of these parts is maintained at an absolute minimum.
  • the only part which tends to be subject to electrolytic dissolution is the anode 110, and it is made of a substance (such as, for example, carbon) which is relatively immune to dissolution.
  • the anode 110 is supported from plate 51a by means of an insulating element 111, and is connected to the positive terminal of a DC current source 112 (comprising a battery 113 and resistor 114).
  • the negative terminal of such source is connected to plate 510 and thus to cylinder 52. Since cylinder 52 touches wheel 55, the
  • a voltmeter circuit is connected to shaft 54 and also to plate 51a (and thus to cylinder 52). Such circuit has I extremely high resistance and draws negligible current.
  • the amplifier output is further connected to a time delay or averaging circuit comprising two series-related resistors 119 and 120.
  • the last-mentioned resistor is connected to one input terminal of a voltage recorder 121.
  • the other input terminal of such recorder is connected to the junction between winding 117 and ground, and also to plate 51a.
  • a resistor 122 and capacitor 123 are connected in series-circuit relationship to each other and bridged across the resistor 120.
  • a second amplifier 124 is provided, having one input connected to the junction between resistor 122 and capacitor 123, and the other input connected to ground. The output of amplifier 124 is connected to the first-mentioned input terminal of recorder 121.
  • the horizontal scale of recorder 121 is related to'time and the vertical scale to voltage.
  • Such voltage is that between surfaces Me and 21e, as amplified and averaged by means of the described circuitry. Stated otherwise, the buildup of contact resistance between surfaces 12e and Me is recorded automatically by the recorder 12], but the averaging circuit prevents the recorder from being sensitive to jiggling or wild fluctuations.
  • the averaging circuitry may be such as to average the peaks, or to average the entire response. Alternatively, the averaging circuitry may be omitted, so that each peak appears in unaveraged manner on the graph of the recorder.
  • circuitry of FIG. 11 may also be employed relative to numerous ones of the previously described methods of sensing contact resistance between the test surface and the auxiliary contactor.
  • the block 130 represents any of the scale-sensing or scale determining devices described above, or any equivalent device.
  • the block 130 may represent the apparatus of FIG.-2, which is associated with a voltmeter 26 shown both in FIG. 2 and in FIG. 12.
  • the voltage sensed by (and the reading of) the voltmeter increases greatly in response to the incipient formation of scale on the test surface incorporated in the scale-sensing means 130.
  • the liquid of a liquid-containing industrial system 131 is circulated automatically through a pipe 132 from such system 131 to the tank or container (corresponding to container 10) forming part of the apparatus 130.
  • a pipe 132 from such system 131 to the tank or container (corresponding to container 10) forming part of the apparatus 130.
  • An automatic mechanism for adding scale (or other adherent precipitate) inhibitor to the liquid of the in dustrial system is represented schematically at 133.
  • Such mechanism 133 includes a voltage-responsive means, for example, an amplifier and associated solenoid, to operate a valve or other device which causes a predetermined quantity of a suitable scale inhibitor (such as one of the scale inhibitors specified above) to flow through a pipe 134 to the liquid of system 131 as soon as the operating voltage supplied to the inhibitor adding means 133 reaches a specified value.
  • a suitable scale inhibitor such as one of the scale inhibitors specified above
  • the voltage output of the scale-sensing means is connected not only to voltmeter 26 but also, by means of leads 135, to the control portion ofthe inhibitor adding means 133, thus supplying the operating voltage referred to in the preceding paragraph.
  • FIG. 5 there is thus illustrated in FIG. 5 one form of closedloop scale (or other adherent precipitate) control for an industrial system.
  • the method may be performed in such manner that the scale-sensing means 130 is caused to monitor the industrial system 131, by having the temperature, liquid impingement and other conditions in the means 130 correspond to those in a critical portion of the system 131.
  • Another manner of performing the method is to cause the temperature (and/or other scale-inducing conditions) in the means 130 to be more likely to form scale than in the industrial system 131, so that a safety margin is provided whereby it is assured that the inhibitor will be added from the means 133 to the system 13] prior to the time that there is any substantial tendency for scale or other adherent precipitate to form in the industrial system.
  • control system After addition of the predetermined quality of scale inhibitor by operation of the means 133, the control system is reset (either manually or automatically) in such manner that an additional quantity of inhibitor will be added automatically, if further scaling is sensed by the sensing means 130.
  • suitable other changes may be made relative to the industrial system 131 in order to prevent continuance of the scaling condition. These may include. for example, changes in temperatures, changes in liquid impingement velocities. change in pH, etc.
  • the method described relative to FIG. 12 may also be performed relative to the instrumentation and method which will next be described relative to FIG. 12a.
  • the scale index for a given liquid (or liquid system) may be achieved by progressively and slowly increasing such factors as l current flow from an auxiliary anode to a cathodic test surface, (2) heat flux (or surface temperature), etc. There will next be described a method whereby such factors are decreased, as distinguished from increased, and automatically stop decreasing when there is a substantial cessation of deposition of scale, etc. Regardless of whether such factors are caused to increase or decrease, the scale index" is that value at which there is a major change in the rate of scale deposition (i.e., a change from a significant rate to 0, or from O to a Sign icant rate).
  • a feedback control circuit 137 is connected between DC source 92 and the input leads to voltmeter 26.
  • Feedback control 137 is so constructed that, when the voltage supplied thereto (through leads 138 and 139) increases, it will effect a corresponding decrease in the current supplied by DC source 92 to the anode 91 and cylinder 94.
  • Source 92 is, at the beginning of the test, caused to supply sufficient current that scaling will result.
  • the feedback control 137 and associated circuitry are such that the current indicated by meter 95 tends to approach asymptotically (in a decreasing direction) the current value at which the contact resistance (between surfaces 12h and 21) stops increasing.
  • Such indicated current value is the highest value, for a given system, at which scale will not continue to deposit.
  • the current passed through meter 95 may be recorded automatically on a suitable recorder.
  • FIG. 12a a system and circuit are schematically represented which effect feedback control of heat as distinguished from current.
  • the mechanical apparatus of FIG. 12a corresponds generally to that of FIG. 6, and has been similarly numbered.
  • the ohmmeter 49 of FIG. 6 is omitted and replaced by a sample and hold circuit 142 which automatically and periodically senses the voltages between surfaces 122 and 21e, stores the sensed voltages, and averages the same to achieve the voltage analog of the average contact resistance present between surfaces He and 212 over a predetermined time period.
  • the connection to sample and hold circuit 142 includes a sampling or updating switch 143 which is operated periodically by a suitable actuating means 144.
  • sample and hold circuit 142 (the voltage analog of the average contact resistance) is supplied through a lead 145 to the input of a servo control amplifier 146.
  • the output of amplifier 146 is, in turn, connected through a lead I47 to the input of a voltagemodulated heater power controller 148.
  • the power output to coil 77 is thus caused to be directly proportional to the control voltage input supplied through lead 147 to circuit 148.
  • Controller 148 replaces (or controls) the power source 80 shown in FIG. 6, and has its output connected through a wattmeter W to the heating element 77.
  • a first recorder, numbered 150 is suitably connected to wattmeter W to record the heating power supplied from circuit 148 to heater 177. Additionally, or alternatively, a second recorder 1152 is connected through suitable circuitry to a thermocouple (or thermistor) circuit 151 which is mounted (by suitable means, not shown) adjacent the test surface l2e of cylinder 52.
  • amplifier 146 The basic design of amplifier 146 is such that its output voltage is proportional to the difference between a set point voltage (corresponding to a desired set point" resistance between surfaces 12e and 216) and the actual analog voltage output of circuit 142. To achieve desired benefits including maximum speed of operation without substantial overshoot, and with the ability to return to the set point value, the output voltage of amplifier 146 may also contain component portions representing terms respectively related to l) the change in contact resistance with time, and (2) the integral of the difference between the set point resistance and the sensed contact resistance.
  • the circuit 148 is caused, initially, to supply to heater 77 an incresing heating power (or to supply thereto a heating power known to be slightly higher than that required to form scale on surface 12e). Then, the heating power supplied to coil 77 progressively decreases in response to the formation of scale (or other undesired adherent substance) on the surface 12e, until there is no further increase in the scale deposit. Such scale formation increases the contact resistance, thus lowering the outputs of circuits 146 and 148.
  • the temperature and/or the heat flux are recorded by the recorders 152 and 150, and each approaches asymptotically a steady-state value which may be defined to be the scaling index of the particular liquid in which elements 52 and 55 are immersed.
  • the surface temperature at surface l2e may be related empirically to the heat input, in such manner that the wattage recorder (No. may be calibrated with a Centigrade scale, thereby eliminating the need for a direct temperature measurement (as by thermocouple 151) at test surface 12e.
  • Another and equivalent manner of practicing the present method is to cause the test surface to have a constant temperature (for example, hot) known to be such as to result in the formation of adherent scale thereon.
  • a predetermined polarity is then applied to the test surface, as by means of the auxiliary electrode 91 of FIG. 9, the polarity (and the magnitude of the applied potential) being selected to prevent deposition of adherent scale.
  • the predetermined polarity of the test surface is anodic, and may be achieved by reversing the polarity of source 92 in FIG. 9.
  • the magnitude of the applied potential is then decreased progressively until scale starts to form,
  • the above assembly was immersed in distilled water, and the heating current was increased until the water was near the boiling point. After 1 hour of this exposure, the contact resistance was measured and found not to have changed.
  • the assembly was next immersed in a saturated solution of calcium bicarbonate which had been diluted with distilled water in a 1:3 ratio (three parts water to one part bicarbonate). Only onetenth of the heat flux which was previously applied to the test rod 46 caused the contact voltage drop to increase from a value near zero (10 to 50 mv) to more than 250 mv, in minutes. At this point, no visible scale was apparent to the unaided eye, however, a much longer exposure showed substantial visual scale deposits.
  • test rod and the control rod were removed from the solution.
  • Each rod was separately tested for variations in surface contact resistance, by rolling it on a smooth surface by means of an auxiliary contacting rod made of carbon.
  • the auxiliary contacting rod was pressed down lightly at right angles and moved lengthwise, so that the rod being examined was rolled without any slippage between contacting surfaces.
  • An ohmmeter was connected between the rod being examined and the contacting rod, whereby to indicate resistance between the rods as they rolled together.
  • the control rod produceed by a contact resistance value that was consistently less than 5 ohms.
  • the test rod produced resistance peaks greater than 50 ohms, despite the fact that the majority of the surface produced less than 5 ohms.
  • An apparatus was constructed similar to that described relative to FIG. 11 (but having a plurality of contactor wheels and a plurality of anodes).
  • the cylinder 52 was made of stainless steel, and the test surface 12e thereon had a length of 5 2 inch and a diameter of /2 inch. All portions of the cylinder 52, excepting surface 12e, were sleeved with Teflon to achieve thermal insulation and to prevent scale deposition.
  • the heated cylinder 52 was rotated 60 revolutions per day by a clock motor. causing the contacting wheel 55 to rotate on its shaft 54 due to the friction contact with test surface l2e. Shaft 54 was mounted in a sufficiently elastic manner that any scale buildup would move the roller 55 away from the surface 12e, without greatly increasing the contacting force.
  • the Contact pressure between surfaces 12a and 212 was about 20 grams.
  • test assembly was immersed in the bicarbonate test solution described relative to Example No. l. at pH 6.8, with the power input to the heater 77 initially at 0. With no heating current, the recorded voltage rcmained at less than 5 m for 15 hours continuous operation. Then the heater power input was raised to 4 watts for a 2-hour period, without any change in the recorded voltage output across the contact interface (this voltage being directly proportional to contact resis tance as measured with the applied current, for this particular assembly configuration).
  • Example No. 3 Using the same apparatus as in Example No. 3. with initially clean surfaces 122 and 212, the assembly was immersed in a similar bicarbonate test solution as in Example No. 3, except that 20 parts per million of nitrilotrimethylenephosphonic acid (scale inhibitor) had been added.
  • Example No. 4 therefore established that the inhibitor at 20 parts per million raised the critical heat flux (scaling tendency) by a factor of about 7.
  • the same apparatus was employed, except that anode 110 was omitted, the DC current source 112 being instead directly connected between cylinder 52 and shaft 54.
  • the test assembly was immersed in purified mineral oil, to demonstrate the ability to measure scale deposits in nonconductive fluids.
  • the apparatus was operated for separate 8 hour periods, first without application of heat and, secondly, with heat inputs increased each hour at 10-watt increments to 70 watts. At all times, the contact voltage drop was lessthan 5 mv.
  • the test was then repeated with a high content of filtered asphaltic crude oil in the mineral oil. Without application of heat, the recorder trace did not increase over 5 mv over a period of 2 hours. With application of 70 watts power to the heating element 77, the recorder trace increased within a few minutes, and gummy depositswere subsequently found on the test surface.
  • MISCELLANEOUS MISCELLANEOUS
  • alternating current instead of the preferred direct current
  • the resulting DC battery voltage may then be used, in place of an external source, to generate the voltage drop between the engaged test surface and auxiliary contactor surface.
  • heating may also be achieved by other means. These include, for example, hot water, steam, quartz-halogen lamp, condensing vapor, and heat-pipe (or other) conduction from a remote source. Whatever the heat source, suitable means are provided to control the amount of heating.
  • the present method contemplates the measure of contact resistance by any means whatever.
  • a Wheatstone bridge or a Kelvin bridge may be employed in place of the ohmmeter circuitry described above.
  • test surface cathodic to achieve a localized pH increase (as set forth, for example, relative to FIG. 9)
  • the invention also comprehends making the test surface anodic to achieve a localized pH decrease. This may be done when the solution is one of those (described above) which deposits adherent substance in response to a pH decrease.
  • test surface may be made anodic when it is formed of a noble alloy such as Inconel, and is used in combination with a contact member formed of a less noble alloy such as stainless steel.
  • voltmeters and ohmmeters are to be regarded as equivalents of each other, since an ohmmeter is essentially a voltmeter incorporating an internal source of power.
  • a method of detecting the deposition, onto a surface, of adherent scale or other adherent substance comprises the steps of:
  • exposing an electrically conductive surface to a liquid of a type which, under at least some conditions, will deposit at least a partial coating onto a surface exposed to said liquid b. detecting an increase in the electrical contact resistance at said surface after it has been thus exposed, said detection of said increase in electrical contact resistance including the step of engaging with said surface a contact element and determining the electrical contact resistance between said surface and said contact element,

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US00335676A 1973-02-26 1973-02-26 Method of detecting the onset of formation of adherent precipitates on surfaces immersed in liquids, and of controlling the formation of such precipitates Expired - Lifetime US3848187A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US00335676A US3848187A (en) 1973-02-26 1973-02-26 Method of detecting the onset of formation of adherent precipitates on surfaces immersed in liquids, and of controlling the formation of such precipitates
DE2407081A DE2407081C3 (de) 1973-02-26 1974-02-14 Verfahren und Anordnung zum Nachweisen der Ablagerung von Kesselstein oder einer anderen anhaftenden Substanz aus einer Flüssigkeit
GB725074A GB1433962A (en) 1973-02-26 1974-02-18 Formation of adherent precipitates on surfaces immersed in liquids
IT48697/74A IT1015819B (it) 1973-02-26 1974-02-25 Apparecchio per la rivelazione dell inizio della formazione di precipiiati aderenti su superfici immerse in liquidi e di controllo della formazione di tali precipitati
JP49022013A JPS5025261A (it) 1973-02-26 1974-02-26
FR7406474A FR2219413B1 (it) 1973-02-26 1974-02-26
US05/509,328 US3951161A (en) 1973-02-26 1974-09-26 Method of detecting the onset of formation of adherent precipitates on surfaces immersed in liquids, and controlling the formation of such precipitates

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Cited By (17)

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Publication number Priority date Publication date Assignee Title
DE2758831A1 (de) * 1977-12-30 1979-08-16 Rohrback Corp Verfahren und vorrichtung zum erfassen und messen von ablagerungen
USRE33346E (en) * 1980-10-30 1990-09-25 Drew Chemical Corporation Process and apparatus for testing fluids for fouling
USRE33468E (en) * 1980-10-30 1990-12-04 Drew Chemical Corporation Process and apparatus for testing fluids for fouling and antifoulant protocol
US5025220A (en) * 1989-09-21 1991-06-18 Ford Motor Company Continuous measurement of the absolute conductivity of a liquid
US5473643A (en) * 1994-08-19 1995-12-05 Westinghouse Idaho Nuclear Company Corrosion testing using isotopes
US5576481A (en) * 1995-10-02 1996-11-19 Ashland, Inc. Method and apparatus for detecting microbiological fouling in aqueous systems
WO1997014034A1 (en) * 1995-09-29 1997-04-17 Ashland, Inc. Method and apparatus for detecting microbiological fouling in aqueous systems
US5810976A (en) * 1996-12-23 1998-09-22 Grand Environmental Corporation Device for processing water having high concentrations of scale forming compounds and high solids content in a high efficiency vapor compression distillation system
US5826601A (en) * 1995-03-30 1998-10-27 Dainippon Screen Mfg., Co. Treating liquid replacing method, substrate treating method and substrate treating apparatus
US5947111A (en) * 1998-04-30 1999-09-07 Hudson Products Corporation Apparatus for the controlled heating of process fluids
US5959194A (en) * 1997-02-13 1999-09-28 Nenniger; John Method and apparatus for measurement and prediction of waxy crude characteristics
US5969235A (en) * 1998-07-02 1999-10-19 Nalco Chemical Company System and method for measuring scale deposition including a tuning fork for use in the system and the method
WO2005054837A1 (en) * 2003-12-02 2005-06-16 Heriot-Watt University Electrochemical sensor for scale building up measurements
US20060169339A1 (en) * 2005-02-02 2006-08-03 Oh Kwang-Wook Microvalve device and apparatus adopting the same
US20120070903A1 (en) * 2008-02-06 2012-03-22 Hydro-Quebec Method and apparatus for measuring the hot-spot temperature in an electric apparatus containing an oil
US20130193080A1 (en) * 2010-09-27 2013-08-01 Pool Technologie Method for managing the reversal frequency of an electrochemical reactor
US20200048564A1 (en) * 2018-08-08 2020-02-13 Jaysun Gillingham Method for separating basic-sediment and water from oil in a crude-oil sample

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Publication number Priority date Publication date Assignee Title
CH598601A5 (it) * 1975-07-10 1978-05-12 Richard Hunziker
JPS52101064A (en) * 1976-02-20 1977-08-24 Futaba Denshi Kogyo Kk Reference surface detector
JPS5334877A (en) * 1976-09-13 1978-03-31 Ajinomoto Kk Rubber lining
CN112730953B (zh) * 2021-01-07 2023-09-01 云南电网有限责任公司电力科学研究院 一种基于电解液分压的高压直流电压测量系统

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US2374088A (en) * 1941-01-28 1945-04-17 Du Pont Corrosion recorder
US3748247A (en) * 1971-12-14 1973-07-24 Betz Laboratories Corrosion probe assembly

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US2374088A (en) * 1941-01-28 1945-04-17 Du Pont Corrosion recorder
US3748247A (en) * 1971-12-14 1973-07-24 Betz Laboratories Corrosion probe assembly

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2758831A1 (de) * 1977-12-30 1979-08-16 Rohrback Corp Verfahren und vorrichtung zum erfassen und messen von ablagerungen
USRE33346E (en) * 1980-10-30 1990-09-25 Drew Chemical Corporation Process and apparatus for testing fluids for fouling
USRE33468E (en) * 1980-10-30 1990-12-04 Drew Chemical Corporation Process and apparatus for testing fluids for fouling and antifoulant protocol
US5025220A (en) * 1989-09-21 1991-06-18 Ford Motor Company Continuous measurement of the absolute conductivity of a liquid
US5473643A (en) * 1994-08-19 1995-12-05 Westinghouse Idaho Nuclear Company Corrosion testing using isotopes
US5826601A (en) * 1995-03-30 1998-10-27 Dainippon Screen Mfg., Co. Treating liquid replacing method, substrate treating method and substrate treating apparatus
WO1997014034A1 (en) * 1995-09-29 1997-04-17 Ashland, Inc. Method and apparatus for detecting microbiological fouling in aqueous systems
US5576481A (en) * 1995-10-02 1996-11-19 Ashland, Inc. Method and apparatus for detecting microbiological fouling in aqueous systems
US5810976A (en) * 1996-12-23 1998-09-22 Grand Environmental Corporation Device for processing water having high concentrations of scale forming compounds and high solids content in a high efficiency vapor compression distillation system
US5959194A (en) * 1997-02-13 1999-09-28 Nenniger; John Method and apparatus for measurement and prediction of waxy crude characteristics
US5947111A (en) * 1998-04-30 1999-09-07 Hudson Products Corporation Apparatus for the controlled heating of process fluids
US5969235A (en) * 1998-07-02 1999-10-19 Nalco Chemical Company System and method for measuring scale deposition including a tuning fork for use in the system and the method
WO2005054837A1 (en) * 2003-12-02 2005-06-16 Heriot-Watt University Electrochemical sensor for scale building up measurements
US20080053204A1 (en) * 2003-12-02 2008-03-06 Anne Neville Electrochemical Sensor
US20060169339A1 (en) * 2005-02-02 2006-08-03 Oh Kwang-Wook Microvalve device and apparatus adopting the same
US20120070903A1 (en) * 2008-02-06 2012-03-22 Hydro-Quebec Method and apparatus for measuring the hot-spot temperature in an electric apparatus containing an oil
US8765477B2 (en) * 2008-02-06 2014-07-01 Hydro-Quebec Hot-spot temperature measurment in an oil containing electric apparatus with a compound forming a temperature dependent oil soluble residue
US20130193080A1 (en) * 2010-09-27 2013-08-01 Pool Technologie Method for managing the reversal frequency of an electrochemical reactor
US20200048564A1 (en) * 2018-08-08 2020-02-13 Jaysun Gillingham Method for separating basic-sediment and water from oil in a crude-oil sample

Also Published As

Publication number Publication date
IT1015819B (it) 1977-05-20
DE2407081C3 (de) 1980-03-20
FR2219413B1 (it) 1977-03-04
FR2219413A1 (it) 1974-09-20
DE2407081B2 (de) 1979-07-05
DE2407081A1 (de) 1974-09-05
JPS5025261A (it) 1975-03-17
GB1433962A (en) 1976-04-28

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