US1855077A - Hot water boiler - Google Patents

Description

April 19, 193 2. wlLDT 1,855,077

' HOT WATER BOILER Filed May 6, 1931 J3v B gmwntw %2z Patented Apr. 19, 1932 UNITED STATES PATENT OFFICE EDWARD A. WIIQDT, OF SCRANTON, PENNSYLVANIA, ASSIG-NOR F ONE-HALF TO JOSEPH W. EARLY, OF SCRANTON, PENNSYLVANIA 1 HOT WATER BOILER Application filed May 6, 1931.

This invention relates to improvements in hot water boilers adapted to retain waterunder pressure and more particularly to 1ron boilers commonly used for domestic purposes.

5 The present application is a continuation 1n part of my earlier application, Serial No. 309,593, filed Oct. 1, 1928.

Up to the present time domestic hot water boilers have been commonly made of sheet iron in various gauges, a coating of protective material such as zinc being applied by means of dipping the articles in a bath of the molten metal. Such articles, in use, have the very serious disadvantage that they soon rust, and after a period of relativelyv few years they are corroded through and become useless. The lives of these boilers can be lengthened somewhat by increasing the thickness or gauge of the metal, but even here the relief is but temporary, as the boilers eventually rust through and become utterly useless. Under the circumstances obtaining in the use of these devices, copper boilers have been found to give a very much greater service, as meas ured by the period of use, however, here also the question of the gauge or thickness of the metal is of paramount importance, as the price of these articles of manufacture in.- creases very rapidly with the gauge thickness. 30 Owing to the relative cheapness and ready availability, sheet iron, of various thicknesses, is preferred for use in making the relatively low priced pressure'boilers intended for use with domestic and like hot water systems. However, as noted above, the substantially uniform high rate of corrosion obtaining in these vessels makes their replacement, after a few years, a matter of necessity.

In addition to the destruction of the boiler itself, these iron boilers, even when initially given a protective metallic coating, upon corrosion discharge or feed into the water lines, an appreciable amount of sediment consisting mainly of hydrated oxides of iron, commonly called rust, which fouls the toilet accessories, such as wash bowls, sinks, bath tubs, etc.

While many theories have been developed as to the cause of the corrosion of these pressure vessels and more particularly of iron Serial No. 535,547.

pressure vessels, the condition undoubtedly is due to whatis commonly called cathodic oxidation.

In the operation of the ordinary domestic hot water boiler, the cold water supply is fed in at the bottom of the boiler, under suitable pressure, and forced into the water block positioned adjacent the fire pot of the stove or furnace with which the boiler is associated. The heated water is fed back into the boiler at a point above the cold water inlet and collects at the top of the boiler. At the junction or interface of the hot water and the residual cold water subjacent thereto, a temperature 'diiferential is established. This difference in temperature is communicated to the metal in direct contact with the hot and the cold water, which temperature difference gives rise to a thermo-electric current whereby the cold metal acts as the cathode of a thermo-electric battery and the hot metal acts as the anode. The hot metal adjacent the interface, above referred to, is eaten away or corroded by these relatively small currents and, if iron forms the metallic surface in contact with the water, the minute particles of the iron set free by this electrolysis are immediately oxidized in the presence of the oxygen in the cold water to form hydrated oxides of iron. These formations are carried by the relatively Weak currents down into the cold water body where they are deposited against the walls of the metal. As the bodyof hot water in the boiler is increased, the hot-cold water interface is progressively lowered with respect tothe boiler,

so that until a body of uniform hot water is present in the container, the inner walls of the boiler are progressively subjected to thermo-electric and electrolytic actions, resulting in corrosion of the metal of the walls. These reactions are constantly repeated, as it is very rare to have an installation in which the water is maintained at a uniform temperature throughout the boiler over any extended period of time.

While, as indicated above, no definite and positive statement regarding the mechanism of the corrosion is possible, the uniform fact v of the corrosion of the boilers has been unlversally kno'w'n. Various expedients have and, in addition,

been proposed to combat this evil. Among these may be mentioned the coating of the vessel on the inside, and on the outside, if desired, with a layer of vitreous enamel. Such coatings do not afford any substantial protection due to thefact that under the influences of pressure and of the relatively greater thermal expansivity of the metal as I compared with the vitreous enamel, the latter soon cracks or flakes ofi, thus exposing'the bare metal to the corrosive influences of the water. Ceramic linings or coatings of porcelain and-the like have been proposed as protective agents for metal containers adapted to contain foods and acid materials, but have not been used in pressure vessels. Rubber has found some application as a lining agent, but it is not suitable for-hot water boilers, due to the destructive action of the hot water. Fibre board or vulcanized fibrealso has been proposed, but as this material contains as an ingredient one or more chemical compounds, such as zinc chloride, which are extremely hygroscopic, this material swells and is soon rendered useless in contact with liquids.

The difficulties arising from corrosive influences in hot water pressure boilers is commonly not 'met with in other domestic appliances such as pots and pans which are exposed to a variety of heated liquids. Here, however, there is no pressure on the vessel,

the liquid contents are in contact with the walls of the vessel for relatively short periods after which the contents are removed.

The use therefore of vitreous. enameled ware for such purposes does not introduce any difliculty, and, in spite of the chipping and cracking of the enamel, the pots are serviceable for extended periods of time. In

contradistinction to this condition, it has been found that vitreous enamel or other water resistant insulating materials, when applied to the interiors of pressure hot water boilers, such as those used in connection with domestic ranges, do not'stand up under the normal operation of ture differences obtaining between the variiron, which, being light and fluffy,

severe conditions imposed, due, as has been indicated above, to the conjoint action of the thermoelectric currents set up during the i the boilers and also to the disruptive effect on the enamel coating of the differential expansions of the metal of the boiler, causing cracking of the vitreous lining, thus permitting access of the liquid contents to the metal.

The chemical reactions between the metal of theboiler walls and the water contained in the boiler, are, as has already been indi cated, greatly facilitated by the temperaous parts of the boiler. The iron of the metal, in contact with the oxygenated cold water, reacts to form various hydroxides of readily sidual rust forming an electric couple with the subjacent metal. The iron hydroxides formed and dispersed in the body of hot water, may, upon long standing, be deposited in the bottom of, the boiler, out of the reach of the ordinary flow of water currents in the boiler, and during this quiescent period, may be further changed to the darker and less voluminous oxides of iron.

While, as has been indicated above, the insulation of the metal lining from the liquid contents of the boiler subjected to pressure is a desideratum and would prevent corrosion of the boiler by preventing contact of the metal with the corrosive influences, the materials hitherto used for this purpose have been characterized by inherentv defects which destroy their usefulness.

It has now been found that by making use of an insulating lin1ng material for the all. the desirable, functions above outlined has been found to be a phenolic condensation product ofthe type commercially available on the market under the trade name of Bakelite. This material is available in a variety of forms which are potentially reactive and which may be applied to the surface of a vessel and then subjected to sufficient heat to convert it into the desired final product which is an infusible resin substantially immune from attack by corrosive agencies.

For the purposes of this invention it is preferred to use the potentially reactive phenolic condensation products in the form of a solution or suspension in a suitable solvent or carrier which composition is particularly adapted for use as a lacquer, such lacquerbeing adapted to be flowed, brushed or sprayed on a surface to be coated and after removal of the solvent to be converted into an infu'sible resin by suitable means. 7

i The use of phenolic condensation products and other infusible resinoids of like characnized domestic hot water boilers have been .ter for the above described purposes has'been' Galvanized and ungalvaprovided with adherent'coating s of Bakelite on the interior thereof and have been subjected to actual d'omestic'use over extended periods without showing any trace whatsoever of corrosion, as, would be evidenced by the presence of rust in the water from the boiler or in that drawn off from the bottom of the boiler. New boilers of the same make exposed to the same general conditions for the same period of time'but without being provided with a protective coating of a phenolic condensation product have been found, upon test, to be corroded, as was evidenced by the presence of rust in the water delivered therefrom.

The purpose of the present invention may be best illustrated by reference to the accompanying drawings, in which Figure 1 is a vertical section of an improved boiler provided with an insulating lining, and

Fig. 2 is a broken vertical section of a water storage boiler illustrating the prior art difliculties.

In the drawings there is shown a metal container mounted on a standard 11, a sup porting block 12 being interposed between it and the boiler, the block being conformed to the curved bottom 13 of the boiler. A cold water inlet pipe 14 extending a substantial distance below the center of the boiler is provided, and connections made from the boiler to a suitable hot water front or other heating device, not shown, by means ofpipe 15, elbow connection 16 and nipple 17 screwed into a threaded boss 17, formed on thebottom of the boiler. A draw-off cock, not shown, may be inserted anywhere in the line 15.

The hot water return pipe 18 is threaded into a boss 19 on the side of the boiler, the inlet thus formed being disposed a substantial distance above the bottom of the cold water inlet pipe 14. A hot water outlet pipe 20 is coupled into boss 21 at the top of the tank. The interior of the tank is provided with a coating 22 of a condensation product such as a phenolic condensation roduct of the type known on the market as Bakelite. This material is applied in a uniform coat over the inner surface of the walls of the container, and is baked so as to form an irreversible water-insoluble resinoid which is characterized by a sufficient degree of plasticity enabling it to expand and contract with the metal of the boiler without differential contraction so that the inner coating does not separate from the metal Wall of the boiler nor split or crack during use.

In the operation of the boiler, the heated hot Water accumulates in the boiler and progressively displaces the subjacent cold water. As the heating period continues a number of interfaces between the body of hot water and the underlying cold water vare successively formed which are designated generally A-A, BB, CC. It will be appreciated that the insulating lining and the metal encompassing the body of hot water above the line A-A will heat the metal while the body of cold water lying below the said line will cool the insulating material and metal of the tank disposed thereabout In the absence of an insulating lining which is adapted to expand and contract equally with the metal of the boiler, the temperature differentials set up in the Walls of the boiler above and below the hot-cold water interfaces A-A, B-B, CC, respectively, will give rise to thermoelectric currents, whose flow in the water is indicated generally at 23, from the hot or anode portion of the boiler to the cold or cathode portion lying in the cold water area, the return flow of current being through the metal of the boiler itself.

These thermo-electric currents cause corrosion of the anode portion of the metal designated generally by the numeral 24, the metal particles being transported through the water and deposited at the cathode or cold water area subjacent the interfaces designated by .the numerals 25. The materials liberated from the anode portions 24 of the tank contacted with the oxygen containing cold water adjacent the cathode portions 25 are converted into hydroxides of iron which are lightly deposited in a voluminous condition on the walls of the tank at the said cathode portions. As the quantity of hot water in the tank increases the hot-cold water interface is progressively lowered along the walls of the tank and the electrical action between the hotmetal and the subjected cold metal is further enhanced by the local action between the previously deposited iron hydroxides and the underlying hot metal, which local action still further increases the anodic corrosion of the hot metal wall of the boiler.

While the currents involved and the corrosion rates are relatively small, it will be appreciated that with constant daily variation in the hot-cold water level in the boiler there is a concomitant variation in the points of attack on the boiler walls so that 115 the entire inner surface of the tank is subjected to the corrosive effect of the thermoelectric currents generated by the temperature differentials in the various parts of the boiler and that this initial corrosive effect is further enhanced by the local action obtaining between the rust deposits of the hydroxides and oxides of iron and the subjacent metal. As the lower portion of the boiler is always the coldest it will be appreciated further that the greatest amount of deposition of corroded material will take place at the bottom of the tank, and this is borne out by observation that the majority of iron boilers corrode most rapidly at the bottom.

If the corrosion were due solely to the action of oxygenated water in contact-with the condensation product on the interior walls; cold metal portions of the inside wall the inof the said boiler. V crease in amount of hot water would be suf- 2. As an article of manufacture an imficient to deaerate the body of water in the proved iron hot water pressure boiler for 5 tank within a relatively short time so that domestic purposes of the character subjected 6 pure oxygen corrosion as such would take. to uneven temperature differentials, having a place but very slightly. coating of an insoluble phenolic condensa- VVhile the temperature differentials in the tion product formed on the interior walls metal of the boiler occur as readily in the thereof to electrically insulatethe same from 10 improved tanks shown in Fig. 1 as they do its contents whereby to prevent corrosion of in the one shown in Fig. 2, the coating or said boiler. insulation of the said inner wall from the .3. As an article of manufacture, a metalbody of the water prevents the flow of therlic container of the character subjected to mo-electric currents generated by the temuneven temperature differentials, lined with perature differentials from the heated metal an insoluble phenolic condensation product 80 to the colder metal through the body of the whereby to prevent electrodic corrosion.

- water. Any transfer of current in the boiler In testimony whereof I affix my signature. system will be from the hot water, back EDWARD A. WILDT. through the cold water pipe 15 to the wall of the boilerand thence through pipe 18 to 85 the hot water front. This circulation, it will be seen, is entirely on the outer surface of the boiler and out of contact with the water contained therein. The small thermoelectrical currents developed in the walls of no the boiler above the pipe 18 will flow from v .the top portion-of the boiler through the feed pipe 14 and that portion of the water in the boiler below the bottom of the said I feed pipe back to the metal at the bottom of the boiler, through the nipple 18.

Here also it will be seen that the inner walls of the boiler are entirely removed from the circuit of these currents and that no cor- 35 rosive influences are permitted to work upon the said inner walls, due to the insulating. coating.

It will now be appreciated that there has been provided an improved means for pre-- I venting the fouling of water supplies due to corrosion of water boilers arising from therinc-electric currents normally generated in the course of operation of said boilers together with the usual corrosive agencies such as prolonged contact of ferrous'materials 1 with oxygenated waters, which improvem'ents involve the coating of the interior walls with an adherent insulating material such as a-phenolic condensation product which material is formed in place into an insoluble resinoid, which resinoid should possess sufiicient plasticity in its irreversible state to permit its expansion and contraction I 55 h he metal subjacent thereto without cracking or separation from the said metal.

What is claimed is 1. As an article of manufacture, an improved domestic hot water boiler of the char entials adapted to contain water under pressure and being characterized by freedom from electrolytic corrosion, including means adapted to prevent corrosion, comprising a protective coating of an-insoluble phenolic "acter subjected to uneven temperature diiferi

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