US2270389A - Apparatus for testing embrittlement characteristics of boiler waters - Google Patents

Description

Jan. 20, 1942. F. G. STRAUB ETAL 2,270,389

APIARATUS -FOR TESTING EMBRITTLEMENT CHARACTERISTICS OF BOILER WATERS Filed Feb. 14, 1938 Patented Jan. 20, 1942 I UNITED STATES PATENTFOFFlCE 2,270,389 i APPARATUS FOR- TESTING EMBRI'TTLE- ,mmr cnnnacrrmsrrcs or comm.

warms Frederick G. Straub, Champaign, and Theodore A. Bradbury, Urbana, Ill., assignors to Board of Trustees of The University of Illinois, Urbana, Ill., a. corporation of Illinois Applicatlon February 14, 1938,

' to cause 4 Claims.

The present invention relates to; an improved apparatus for determining the embrittlement characteristics of boiler waters.

A11 prior devices for this purpose, with which wearefamiliar, have not given suflicient certainty and accuracy in their performance to insure reliable test data. Such prior devices frequently give conflicting or irreconcilable results on successive tests and, even when operated under the most rigorous conditions, give results which are so variable as to meanthat any flndings based thereon can, at best, represent only rough approximations. One of the objections to these prior devices is that they do not simulate with any substantial degree of accuracy the physical and chemical conditions which are, actually present in a boiler. Some of the diillcul- V ,ties encountered can be illustrated by reference to caustic Iembrittlement caused primarily by sodium hydroxide (NaOH). Prior/experimental:

work has indicated that a substantial sodium hydroxide content in {boiler water contributes materially toward embrittlement, this constituent entering in the form of sodium carbonate in the feed water, which rapidly breaks down to form sodium hydroxide in the boiler. Embrittlement occurs almost exclusively in riveted seams, tube ous consequences of boiler explosions arising from embrittlement make it all the more imperative that test data on the embrittlement characteristics of boiler waters be accurate and reliable. I

Another factor which appears to be of importance in causing embrittlement is stress in the metal. Embrittlement cracking is practicallv always intercrystalline, i. e., following the grain boundaries ofthe metal, and this cracking appears to be accelerated by increasing the tensile stress in the metal. Hence, complete testing of the embrittlement characteristics of different boiler waters, and complete testing of the resistivity of different boiler steels and alloys to the action of embrittlement, requiresthe ability to put the test specimen of metal under varyingdegreestoi stress.

The devices which have ployed to make such tests have been particularly inadequate from the standpoint of accurate dejoints, the flanges of blow-off connections, and.

other joints and seams which are below water level. Proofs established to date show rather conclusively that the sodium. hydroxide enters even the most minute capillary spaces in these seams or joints and tends to create a concentrated caustic solution therein. The concentration appears to be brought about by an out- H ward flow of steam bubbles from these capillary spaces and an inward flow of water into said spaces, the inward flow of water tending to carry additional caustic into the capillary spaces and ,thereby tending to increase the concentration of the, solution therein. Such outward flow of steam and inward flow of water is intensified. with various fluctuations or changes occurring in the boiler operation, i. e., fluctuations in steam pressure, in temperature, in water level, and the like. Frequent blowing down of the boiler and other attempted remedies of a mechanical nature seem to be of. little avail for preventing such concentrated caustic solutions from collecting in the capillaryv spaces, or for removing them from the spaces once they have collected therein. As a result, the concentration of sodium hydroxide keeps on increasing until after sufflcient time,

, caustic embrittlement of the metal adjacent to the capillary space occurs to a su'ificient degree termination of the concentration of the sodium hydroxide solution. The concentration which would be likely to arise in a typical capillary space of a conventional boiler supplied with feed water of known properties and operating under typical conditions has heretofore been largely a matter of guess. Hence, prior efforts to test boiler waters by first making up a solution in which the sodium hydroxide is of known concentration and then introducing this solution into the testing device have not been dependable because of the uncertainty of knowing the concentration which would be likely to arise in a capillarys'pace under the typical conditions above mentioned. This difliculty is decidedly in- I creased wherethe actual boiler waterto be tested contains varying proportions of sulphates,

chlorides, phosphates, or other constituents which may either accelerate or inhibit the embrittling action of the sodium hydroxide. The degree of concentration which any of these more involved solutions or'compoundswould be likely to develop in a capillary space'is almost entirely conjectural. cacy' of different chemical agents to be introduced into objectionable boiler waterin order to inhibit embrittlement have been rendered difflcult and uncertain because the proper concentrations to be employed in the test solutions have not been known.

Another objection to some of these prior devices for testing embrittlement characteristics eboilr to leak or explode. The seriheretofore been em- Thus, efforts to test theeiiiused in the boiler.

has been the laborious work involved in conducting such tests.

One of the principal objects of the present in- I vention is to provide animproved apparatus for testingthe embrittlement characteristics of boiler water whichfwill simulate with a high degree of accuracy the actual conditions occurring in a typical boiler. To this end, according to the preferred practice of our invention, thesolution to be tested is boiled in a chamber whichis characterized'by an upper chamber area, a} lower capillary space, and a restriction which establishes' communication between the. upper; chamber area and said lower capillary space. The restriction functions in the nature ofa valve for allowing steam to travel in one direction and .the solution to travel in the other f direction.

That is to say, bubbles of steam in the lower capillary space are caused to pass upwardly through said restriction into said 'upper chamber area, andsolution in said upper chamber area is caused to pass downwardly through said restriction into said lower capillary space. With steam constantly leaving the lower capillary space, the solution concentrates therein. Each additional amount of solution entering the lower capillary space .brings with it a small additional amount of sodium hydroxide ,or other chemicals which may be present in the boiler water being tested. The action simulates an extremely intense or rapid activity of a typical capillary space within a boiler, corresponding to extremely rapid fluctuations in steam pressure, in temperature, in water level, in blow-off operations and the like. Thus,- the test accelerates in point of time'the concentrating action'of a typical capillary space within'a boiler. By virtue of this mode of operation, the solution which'is introduced into the testing chamber can be of the.

same degree of concentration of all of its constituents as is actually used or intended to be Thus, the elements of uncertainty in obtaining the proper proportions and concentrations for prior testing methods have been eliminated.

Another object of the invention is to provide an improved means for establishing any desired degree of stress in the metal which is being subjected to the embrittling action of the solution during the test. According to the preferred embodiments of the invention, this metal constitutes the outer wall of the test chamber, and

Other objects and advantages of theinvention will be apparent from the following detail description of the preferred embodiment of the invention.

In the accompanying drawing: 7 Figure 1 is an axial sectional view, partly broken away, showing our testing apparatus; and

' Figure 2 is a sectional view on showing the lower capillary portion of the test ing chamber.

'Referring to Figure l, the vertically spaced horizontal plates 1 and 8 represent the. top and bottom walls of a testing table or other suitable supporting structure, preferably accommodating a suitable number of these testing units, indicated generally at 9. testingunit 9 is adapted to be inserted down into a cylindrical shell II which is secured between the upper and lower plates 1 and 8. The lower end of said shell preferably seats in an annular groove I2 formed in the lower plate 8, and the upper end of said shell fits within a circular opening l3 formed in the upper plate 1. En-

circling said shell is an electrical resistance ele-v adapted to be detachably secured to the top surface of the upper supporting plate I, over the furnace cell I I, through the instrumentality of suitable securing devices such as the bolts H, or studs secured to the plate I and adapted to extend. up through apertures in the mounting plate IS. A cylindrical sleeve l8 extends downwardly from the mounting plate I6, such sleeve serving to sustain the tensile stress transmitted through the test chamber, and also serving to confine the steam and hot liquid upon fracture of the test chamber. The upper end of this confining sleeve I8 is removably seated in an annular groove l9 formed in the underside of the mounting plate l6, and the lower end of said 'dicated in'its entirety at 24, the lower intermediate portion of this chamber being formed with a larger scale 76 4 1;

a reduced wallthickness 25'where fracture occurs when the chamber is disrupted. The lower end of the specimen is provided with an enlarged threaded head 26 which is adapted to screw into a threaded bore 21 in the end cap 22. The upper end of the specimen is threaded at 2-3 for screwing into a tapped bore 29 in the lower end of a coupling head 3|. A closure plug 32 of suitable material is seated in the upper endof the bore 29, the upper end of the testing member being forcibly screwed against this closure plug so as to form a pressure-tight joint.

A tension rod 33 passes downwardly through an opening 34 in the mounting plate I8 and has a lower threaded end 35 which is screwed into a tapped bore in the upper end of the coupling block 3|. Surrounding this rod on the up er side of the mounting plate I6 is a cylindrical spacing sleeve 31 which has its lower end removably mounting plate. The upper end of said sleeve is removably seated within an annular groove.

33 formed in the underside of a circular pressure plate ll through which the rod 33 passes. Adjustably mounted on the upper portion of said rod is a thrust plate 42, and.confined between this thrust. plat and the lower pressure plate The lower end of ..each I a heavy compression spring 43. A nut 44 conductors 53 and 54 screwing downwardly over the threaded upper end 45 of the spring rod 33 adjusts the position of the upper plate 42 and thereby enables any desired compression pressure to be established in the spring 43. The stress of said spring is transmitted in an upward direction through the spring rod 33 so that this stress establishes a tension in the thin-walled portion 25 of the testing chamber 24. instantly indicating the fracture of the thinwalled portion 25, we have adopted the practice of pasting a strip of paper 41 to the edges of the upper and lower thrust plates 42 and 4| as As a convenient expedient for soon as the desired pressure has been established a catedat 5| and 52; being peend into holes previously drilled in the test chamber 24, preferably at a point Just above the thin-walled Portion 25. Leading from these thermocouple elements are which pass upwardly through one or more apertures in the mounting plate l6 and which then extend outwardly through one'or mpre apertures in the 'upper spacing sleeve 31. The use of these thermocouples and the connection thereof. with suitable regulating, indicating or recording apparatus, is

old and well known and need not be described in detail.

Referring now to Figure 2, the interior of the testing chamber 24 is divided into different cham ber area-s by disposing a removable metallic plug or filler 55 inthe lower end of the chamber portion 51 of slightly larger diameter than the main shank of'the plug. The disposal of the plug in-the bore serves to divide the bore into a plurality of chamber areas. For example, the space above the plug constitutes a relatively large chamber area 24a, whereas the space below the head 51 of the plug constitutes arelatively small chamber area 24c. This small chamber area can be made of different proportions relatively to the upper chamber area 24a, as desired, although it is preferably. formed of'relatively small size so that it functions analogously to a capillary space v in a boiler. The space surrounding the upper head 51 of the filler plug 55 is. of still smaller size, this space constituting a restricted passageway 241' which establishes communication betion into the furnace.

cold loaded" or with the specimen hot loaded." If the specimen is to be cold loaded, the spring load is imposed on the test chamber with the apparatus in a cold state, prior to its introduc- V In this procedure, the furnace may be brought up to the desired temperature after the testing unit has been placed therein, although, preferably, the furnace is heated to the desired temperature before the testing unit is inserted therein. If the specimen is to be hot loaded, the testing unit is inserted into the hot furnace with no substantial spring pressureimposed on the testingchamber; it is main tained in the furnace in this condition at. a desired temperature for a definite period, and thereupon the spring load is imposed on the test chamber by screwing the nut 44 downwardly along the threaded end 45 of the spring rod 33. Hot

loading usually results in fractures of the testchamber at lower temperatures and lower spring pressures than col/l loading.

The boiling of the solution 6| results in a relatively rapid rate of steam generation within the relatively small volume of liquid confined in the capillary space 240. As previously described, these bubbles of steam pass upwardly from the capillary space through the restriction 241' into the upper chamber area 24a and steam space 52.

With this emission of steam from the capillary capillary space back into the. upper chamber area.

Each additional amount of solution traveling down into the lower capillary space 240 brings with it a small additional amount. of sodium hydroxide and such other chemicals as may be present in the solution being tested. In this manner, a concentration of these chemicals rapidly accumulates in the capillary space. As previously stated, the action simulates an extremely intense or rapid activity of a typical capillary space within a boiler, corresponding to extremely rapid fluctuations in steam pressure, in temperature, in water level; in blow-off operations, and

the like. Thus, the. test may be made to accelerate, in point of time, the concentrating action of a typical capillary space within a boiler. By virtue of the fact that the concentration is effected in a manner analogous to the way in which a capillary space within a boiler effects concen-, tration, the results obtained are an accurate measure of the embrittling characteristics of the solution. Furthermore, the uncertainties residing in the previous practice of preliminarily concentrating the solution before introducing it into a test specimen are completely eliminated.

It will be understood that if the solution has embrittling characteristics, an intercrystalline cracking will start in the thin wall section 25 of the chamber, such cracking working progressively outwardly from the inner to the outer surfaces of said section, substantially as indicated at 54. When the strength of the wall is reduced below that of the tensile stress imposed thereon, the specimen disrupts endwise and the steam and hot liquid is vented into the confining sleeve l8. Because of the relatively small capacity of the test chamber, no damage is done when the contents of the chamber explode into this confining sleeve. The striking of the coupling head 3| against the underside of the mounting plate I 6 limits the upward movement of the spring rod 33. The duration of the test before fracture, if fracture occurs, the temperature, and the spring loading, are all factors which are considered when making isolated or comparative tests to determine the embrittling characteristics of natural boiler waters or of synthetic solutions containing agents intended to inhibit embrittlement cracking. v

The provision of the restriction 241' in the test chamber is not essential, but such restriction is advantageous. For example, it represents the most adverse or aggravated instance of a capillary space within a boiler, corresponding to an outlet therefrom which; is so restricted or so positioned or located that egress of liquid therefrom is decidedly restricted. It is also within the .purview of our-invention to vent steam atthe upper end of the chamber area, if desired, but we deem it preferable to maintain'the chamber sealed, thereby avoiding an artificial concentration of the solution and more closely approximating actual conditions within a typical boiler.

The cross-sectional area of the test specimen of inetal isrelatively small, so-that the external source of force or energy required to maintain this specimen under tensile stress loads of from upper chamber area, a lower capillary space and a restriction which establishes communication between the two, said chamber comprising an' enclosing metallic wall of known characteristics which is subjected to the embrittling action of I .the water in said capillary space, means for establishing a stress in said enclosing metallic wall, and means for boiling the water in said chamber to cause bubbles of steam in said capillary space to pass upwardly through said restriction into said upper chamber area and to cause water in said upper chamber area to pass downwardly through said restriction into said capillary space, whereby to effect a concentration of the emb'rittling constituents of the water within said capillary space in simulation of conditions with in a typical boiler.

2. Apparatus for determining the embrittlement characteristics of boiler waters and the like, comprising achamber adapted to receive a specimen of the boiler water to be tested and formed with a relatively large chamber area, a relatively small capillary space and a restriction which establishes communication between the two, said chamber comprising an enclosing metallic wall of known characteristics which is subjected to the embrittling action of the water in said enclosing metallic capillary space, means for estabnevertheless it"will be understood that such "is merely exemplary and that numerous modifi cations and rearrangements of structure and operation may be made without departing from the essence of the invention. For example, while we prefer to maintain a tensile stress in the test specimen of metal through an external source of force or energy, as -exemplified bythe action of the spring exerting a tensile stress in the wall of the chamber 24, we also regard it to be within the scope of the invention to dispense with this external source of force or energy and to rely upon the internal pressure of the steam alone to stress the test specimen of metal.

We claim: 1. Apparatus for determining the embrittlement characteristics of boiler waters, comprising a chamber adapted to receive a sample of the boiler water to tested and formed with an" lishing a stress in said enclosing metallic wall, and means for boiling the water in said chamber to cause bubbles of steam in sad capillary space to pass therefrom through said restriction into said relatively large chamber area and to cause water in said relatively large chamber area to pass therefrom through said restriction into said capillary space.

3. Apparatus for determining the embrittlement characteristics of boiler waters and the like, comprising a chamber adapted to receive a specimen of the boiler water to be tested and formed with a restricted. capillary space, said' chamber comprising an enclosing metallic wall of known characteristics which is subjected to the embrittling action of the'water in said capillary space, means for boiling the water in said chamwithin said capillary'space,and means for subjecting said enclosing metallic wall to stress in the testing operation. v

4. Apparatus for-determining the embrittlement characteristics of boiler waters and the like, comprising a chamber adapted to receive a specimen of the boiler water to be tested, aflller member in said chamber comprising an enlarged head portion said filler member dividing said chamber into an upper chamber area, a lower capillary space and a restriction which establishes communication between the two, means for creating a tensile stress in said chamber, and means for boiling the water in said chamber.

FREDERICK, G. S'I'RAUB. THEODORE A. BRADBURY.

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