US2283954A

US2283954A - Apparatus for testing the embrittlement cracking characteristics of solutions

Info

Publication number: US2283954A
Application number: US234722A
Authority: US
Inventors: Wilburn C Schroeder; Abraham A Berk
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-10-12
Filing date: 1938-10-12
Publication date: 1942-05-26
Anticipated expiration: 1959-05-26

Description

.mesas May 2e, i942 @finira naar erstes l APPARATUS FOR TESTENG .THE Eml'll- 'ELEMENT CRACKING HARACTEBSTHCS OF SOLUTIONS resented bythe Secretary of his successors in omce Application october 12, 193e, serai No. 234,722

' (ci. 1e-.51)

(Granted under the act of March 3, 1883, as

amended April 30, 192%; 370 0. G. 757) 5 Claims.

The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes only 'without the paymentl of any royalty thereon.

'This invention relates to an apparatus for testing the embrittllng or intercrystalline cracking characteristics of water used in an operating boiler or of solutions used in other metal vessels. I

Serious diiculties from embrittlement in boilers, digesters, etc., have been encountered and recognized for a number of years. Investigation has clearly shown that dilute` alkaline solutions, such as used in boiler operation, will notcause embrittlement cracking.- .For example, water in a boiler will seldom c ntain more than a few thousand parts per mil ion of sodium hydroxide, and at such a degree of dilution, the watercannot cause embrittlement cracking of tube ends,

riveted seams, etc. In the laboratory, it has been found that from 50,000 to 500,000 parts per million of sodium hydroxide are usually necessary to cause cracking.

Our investigations have shown that if a dilute boiler water, or solution, is concentrated by evaporation it can produceembrittlement cracks and failures in steel which is maintained under stress in contact with such concentrated solution. Concentration easily can be accomplished by withdrawing a sample of water from the boiler and evaporating it until it contains from 200,000 to 500,000 parts per million of sodium hydroxide. Such concentrated solution, heated to the atmospheric boiling temperature, or to a higher temperature under pressure, can be placed in contact with a stressed steel specimen, and if intercrystalline cracking results, the water is a dangerous one and may cause embrittlement cracking in the boiler metal.

Concentration of the dilute water solution also can be produced directly in contact with a stressed specimen instead of being concentrated and later brought into contact with the specimen. A number of tests have been made with apparatus of this character wherein the dilute boiler Water has been placed in a receptacle` having a small space one wall of which is formed by the stressed specimen to be tested, andthe device is placed in a furnace or other heating equipment to be brought up to the temperature the: interior and at which it is desired to conduct the test. Steam thus generated is slowly bled 0E to permit concentration of the boiler water in the device, which is commonly known as a bomb The small space referred to is usually annular and by making such space quite narrow, itis possible to concentrate the boiler water many hundredfold. The stress can be applied tothe specimen in any 4desired manner, either internally or externally,

and it may be provided before the test is started and/or at any time during the test.

If the initial sodium hydroxide concentration of the boiler water is known, the nal concentration attained in the bomb can be determined by condensing and measuring the steam which is driven ofi. The solution can be maintained at any desired concentration by closing a bleed valve.

.Concentration of the dilute boiler water also can be secured without actually bleeding off steam from the device. For example, if a closed contalner is provided with a depending hollow member in which the specimen is arranged, and

whereinl small clearance is provided between the specimen and the depending hollow member, heat may be applied to such member. conditions, steam will be generated in the small space adjacent the specimen and the steam will pass upwardly into the receptacle, thus leaving a concentrated solution in contact with the'specimen. As' in the previous case, the specimen may be maintained under stress in any desired manner to determine whether embrittlement cracking o f the metal will occur. f

In steam boiler operation, or in other metal vessels, embrittlement crackingv is found in rivets, butt straps, drum sheets, tube ends, etc., that are at the same temperature as the boiler water and therefore could not cause solution concentration by evaporation against the boiler pressure or evaporation in accordance with the test methodsreferred to above. This obviously is true for the reason that the rivet heads and other elements referred to do not have sources of heat supply which could cause the evaporation. f

In the testing methods referred to above, concentration of the boiler water or other solution requires that a specimen of the water be removed from the boiler or other vessel or isolated in a Under such y separate vessel attached to the boiler with suittions that produce cracking in either of the test methods referred to are not necessarily the'same as those that cause embrittlement of the metals comprising the parts or elements of the boiler or vessel. 1

An important object is to provide a novel apparatus for testing the embrittlement cracking characteristics of boiler wateror other solutions wherein actual operating conditions are reproduced.

l `A further object is to provide a novel apparatus of the character referred to wherein the Solution is led directly from the boiler or other vessel over a test specimen undervv conditions reproducing actual conditions within the Aboiler or other vessel whereby any changes occurring in -the boiler will be reproduced during the practice of the method and thus provide accurate information as to the characteristics of the solution.

A further object is to provide a novel apparatus wherein water or other solution from a lboiler or other vessel is led directly over a specimen to be tested in a reduced restricted 'flow whereby concentration of the solution will occur against the specimen to reproduce conditions which are occurring within the seams or other restricted spaces in a boiler or on other metal surfaces in of the present invention4 other vessels at points where embrittlement' cracking usually occurs.

Al further object is to provide such an apparatus wherein evaporation of the solution takes place from the side of the specimen opposite that at which the solution is fed thereto to eiIect a tus wherein the normal operating conditions in a boiler or the like are accurately reproduced so the present invention, therefore, water is led directly from the boiler or other vessel into the testing device and -a flow of the water is provided at a slow rate through a restricted space one `wall of which is formed by the test specimen. approximate boiler temperature being maintained atthe test point to assist in simulating or reproducing' actual conditions at points within a boiler or the like where embrittlement cracking takes place. During passage through the restricted space pressure is released and steam escapes toward the atmosphere through an loutlet pipe preferably controlled by a bleed valve whereby the rate of flow of the escaping fluid canv be controlled, such iiuid, of course. being in the form of steam developing incident to the releasing of the pressure.

The rate-at which pressure is released by per- Y mitting the escape of steam, together with vthe restriction ofthe space throughwhich the solution ows past the speciment'will determine the rate of ilow of the solution past the specimen, and accordingly any desired rate of concentration adjacent to the specimen can be provided. This restricted space, as indicated above, constitutes a simulation of conditions that exist in a riveted seam or rolled in tube end or other place in a boiler in which embrittlement cracking is commonly encountered. As vthe boiler water passes through the seam or rolled in tube end it 'progresses toward a region of lower or atmospheric pressure and therefore due to its high temperature this drop in pressure causes the escape of steam toward the atmosphere and the consequent concentration of the solution remaining in the-restrictedpassage. :The conditions created in the equipment described in this inthat the results obtained by the apparatus are accurate indications of the embrittlement characteristics of the solution inthe boiler or the like.

A further object is to -provide an apparatus yhaving a restricted passage for the iiow of boiler water or the like directly from the boiler or other vessel and wherein a specimen under stress forms one wall of the restricted passage, and wherein evaporation of the solution and the concentration thereof will occur in contact with then specimen to reproduce conditions within the boiler or other vessel.

A further object is to provide a novel apparatus of the character just referred to wherein evaporation is caused to take place at the end of the restricted passage opposite the end to which the solution is introduced to facilitate the concentration of the solution in contact with the specimen.

Other objects and advantages of the invention will become apparent during the course of the following description.

We have discovered that the conditions under which embrittlement cracking occurs in boilers or other vessels may be closely simulated or exactly reproduced so as to render a test device of this general character far more accurate and vention duplicate these conditions existing in4 the riveted seams or rolled in tubes' or other restricted spaces in the boiler.

The specimen being tested obviously is maintained under stress during the test,' and the stress may be internal and/or external, and it may be applied before or'during the test and 4;,- maintainegl throughout the test. It will be apparent therefore that the test exactly duplicates the conditions that cause embrittlement of the rivets, butt straps, etc., and'can be operated con- .4 tinuously on the boiler or vessel so that'any change which creates a dangerous condition in the water will be immediately discovered. With dependable in its results. In accordance with 76 the proper instructions, the test can be conducted without specialskill or training, and complete control is provided over thegoperation of the equipment. In waters or solutions that are treated to render them incapable of producing embrittlement cracks, the test obviously` can be used to estimate the eil'ectiveness of the treatment employed.

have indicated .that the solution from a steam boiler or other vessel may be very easily concentrated to produce embrittlement cracking by allowing it to leak or diffuse through a small .opening more slowly than it is permitted to evaporate on the other side' of the leak or opening by protviding the steam escape control means referred In the drawing we have shown several types of apparatus particularly adapted for practicing the method. In this showing,

Figure 1 is a sectional view showing one type of apparatus wherein the specimen is spring loaded to be maintained under stress,

Figure 2 is a similar view of a modified form Somewhat more specically; our experiments 2,283,954 .tot theinvention wherein the spring loading is transmitted to the specimen longitudinally thereof and is supplemented by lateral .stressing means,

Figure 3 is a similar View showing another modification wherein a substantially cylindrical specimen is maintained under stress by being driven into position on a plug or the like, and,

Figure i is a similar view of afurther modiflcation wherein a conical stretcher is employed -or the specimen and wherein the ow space pates a receptacle shown in the present instance as in the forni of a cast body having a passage il therethrough into one end of which is thread-l ed a pipe i2 connected to the boiler or other receptacle to feed directly therefrom the water or other solution to betested. A pipe I3 is threadedin the other end of the body w and is provided with a take-od' pipe It preferably provided with a control valve le, and the pipe le preferably leads to a suitable condenser.

Between the adjacent ends of the pipes l2 and i3 a test specimen indicated as a whole by the numeral it is arranged within the passage li,.

the space Il surrounding the specimen constituting a solution concentrating chamber, as will become apparent., The specimen is hollow, as shown and is provided at its lower end with an A annular flange i8 forming a restricted annular 'passage it for the iiow-of water. The upper end of the flange ld engages lugs 2d, extending intoV the bore il, to limit upward movement of the specimen. The specimen is provided intermediate its ends with a relatively thin cylindrical wall 2l at some point along which the embrittlement cracking is adapted to occur.

The specimen is provided at its upper end with a head 22 through which extends a stem 23 having a head 2d at its lower end engaging the lower face of the head 22 to exert an upward force for maintaining the specimen under stress, as will become apparent. The stem 23 extends through a plug 25 mounted in the upper endv of the pipe i3. A spring seat 25 surrounds the stem 23 at a point spaced from the plug 25, and arelatively heavy compression loading spring 2l surrounds the stern 23 between the plug 25 and spring seat 26. A thrust bearing 2B is preferably arranged above and in engagement with the spring seat 2d, and a n ut 23 is threaded on the upper end of the stem 23. The upper extremity of the stem 23 may be formed polygonal as at et for engagement with a wrench to prevent turning movement of the stem 23 while the nut 29 is being turned.

A particularly advantageous form of the invention is shown in Figure 2 wherein the speci- :men is subjected to both axial and transverse stresses. A body 3l is provided with a chamber 32, and a cap 33 in the lower end of the body is tapped as at 34 for connection with a pipe leading to the boiler to supply boiler water lto the chamber 32. The body 3l also may be provided with an opening 35, connected to the boiler,

'l threaded at its upper end as at l2 for a purv pose to be described'. The stem il! extends downwardly through the upper end of the body 3| and is provided with a reduced test portion 3 withinthe space 36. Below thev test portion the specimen is provided lwith a. conical portion 4d for at leastv partially closing the seat 33. Below the conical portion 4t the specimen is provided with a depending cylindrical portion d5. A suitable packing gland dB may be provided to prevent lealrage pastthe stem l The body 3l yis provided near one side-with a threaded opening for the reception of a plug il in which is arranged a stem da, this stem being provided with a threaded portion de engaging a similarly threaded opening in the plug al. The

inner end 5t of the stem a is engageable against the lower end a5 of the specimen and it will be apparent that upon the application of a wrench to the polygonal outer end 5l of the stem ed, the latter may be turned in the plug lll to cause the inner end 5!) ofthe stem to exert a lateral force against the lower end t5 of the specimen. The

stem t8 may extend through a suitable packingv gland 52 carried by the plug el.

A supporting sleeve 53 has its lower end threaded on an axial extension 54 carried by the body 3i, and the upper end of the sleeve 53 carries a spring seat 35. A stem 56 has its lower end extending into the sleeve 53 and enlarged as at 5l to receive the threaded upper-end d2 of tension of the spring 59. The upper end of the stem 56 may be made polygonal as at 62 to be engaged by a wrench.l and thus hold the stem 5B against turning while the nut t! is being adjusted. It will become apparent that the spring 59 exerts an upward force on the stem 56 to maintain the specimen under a static tensile load.

whereby a circulation may be maintained through thin substantially cylindrical specimen 'l2 which ln`the form of the invention shown in Figure 3 a body S3 is provided with a passage 64 into the lower end of which is tapped a pipe t5 to supply Water from the boiler or other nozzle. A cap member 6 5 is threaded in the upper end oi the bore and is provided with a steam escape pipe 6l. This pipe also may be provided witha control valve 68 and may lead to a suitable condenser. A specimen support 69, in the form of a substantially cylindrical plug, is supported in the passage 64 by lugs l0 and may be held in the position shown in Figure by a suitable spring The plug 69 is surrounded by a relatively is driven into position on the plug 69 to be thus maintained under substantial tension. The passage M forms a chamber 13 within the body B3 and the lower end of this chamber is defined by the relatively narrow annular space 'M surrounding the specimen 'I2 and forming a solution coni centrating space, as will become apparent.

threaded a stem 80 having a conical head 8| at one end. A specimen 82 is formed oi' relatively 'thin steel and coincides in shape and size to the conical head 8| to surround the latter. 'I'he smaller end of the head 8| is threaded as at 83 to receive a nut 84, whereby the specimen 82 may be ,forced toward the larger end of the head 8| to be placed under static circumferentialtension. Between the head 8| and the plug `18, the body is ported as at 85 Vfor connection with a pipe 86 which may lead to a conventional condenser.

spaces of slow flow within 'a boiler at which V points embrittlement cracking usually takes place. l

in the annular space around the test portion '2| of the specimen. Either steam or a solution more dilute than that entering through the pipe I2 must be taken off through` the pipe I4. In a test equipment, the device has been connected to a pressure vessel containing 2,000 parts per million of sodium hydroxide at 200 lb. gage pressure, and it was possible to tap off almost pure steam through the'pipe I4 and leave 0.3 gram of sodium hydroxide in the annular space surroundingthe test portion of the specimen. The actual sodium hydroxide concentration reached in such space was greater than 500,000 parts per million.

The form of the invention illustrated in Figure 2 is quite similar to that shown in Figure 1 except ythat the specimen is of a dierent type and is subjected both to axial and transverse stresses.

After the spring 58 has been provided with a predetermined loading, which obviouly will hold the conical element I4 on the seat 31 to act as 4a valve therea'gainst, the stem 48 may be turned Pressure is released by opening the valve I5 to the proper extent. in which case the boiler water is converted into steam at a rate'depending upon the degree of opening of the valve I5. This action causes concentration of the solution in the space around the test portion of the specimen. It will be apparent that the space around the annular shoulder I8 is somewhat exaggerated and in actual practice only a slight leakage 'is provided so that there will be an extremely slow flow of solution into the chamber I1.

The spring 21 is relatively heavy and its tension is adjusted by turning the nut 28, preferably while engaging the polygonal head with a wrench to prevent the turning of the stem 23. It will be apparent that the spring- 21 exerts an upward force on the upper end of the'specimen while the lower end of the latter is engaged by the lugs 20 to prevent its upward movement. Accordingly the spring 21 acts to maintain any 'desired static tensile load on the specimen.

As is true in all forms of the invention shown,

' the device in Figure 1 meets the essential requirement that self-evaporation in theL boiler water or other solution takes place while in contact with the stressed specimen. The device operates by allowing leakage or diffusion of the solution through a small opening provided around the flange I8 more slowly than evaporation takes place on thelother side of the leak, and accordingly self-evaporation takes place in contact with the specimen, as stated. It will be apparent that the connection of the device with the boiler or other vessel renders the device sensitive to any changes which take place in the source` of the solution, and the heat of the source is main-- 'tained as well as the pressure in the source except for the slight drop in pressure occurring incident to the opening of the valve I5. vIt will apparent that after a period of time concentration takes place in contact with the'specimen in the same manner that it takes place adjacent to the metal or parts in the boiler which are usually subject to embrittlement cracking, and if such cracking of the specimen takes place, the solution may be dangerous for use in a boiler.

The leakage which takes place 'around the flange I8 must be slow enough so that the solution canevaporate and deposit its dissolved solid inwardly to exert a lateral force against the lower end 45v of the specimen.x 'I'his operation provides a lateral stress against the specimen and also suiiiciently unseats the conical member M at the side adjacent the stem I8 to 'permit a leakage between the chamber 32 and` the concentrating 'space 36.

The pipe 39, of course, `will be valve controlled to determine the rate of exhaustion of steam from the space 36 and consequently the rate of evaporation therein. Concentration of the solution in the space 36, therefore, renders the device in Figure 2 similar in this respect to the operation of the device shown in Figure l. Themechanism shown in Figure 2 is advantageous in that it provides the two different stresses referred to and for the additional reason thatit provides communication through two openings (34 and 35) with the boiler or other vessel to maintain a circulation through the chamber 32 so that the solution therein will always correspond to the solution in the boiler or other vessel regardless of any changes which take place therein. Accordingly the device closely simulates or reproduces conditions .in the boiler or vessel. As in the form previously described, embrittlement cracking of the specimen indicates that the use of the solution is dangerous. In both of the forms of the invention described, breakage of the specimen is immediately visually indicated by the releasing of the stem 23 or 56 by the springs acting upwardly thereagainst.

The form of the invention shown in Figure 3 is simpler than the form described but provides no visible indication of breakage of the specimen. `Very slow leakage takes place around the lower end of the plug 69, the space through which this leakage takes place being exaggerated in Figure 3. Leakage of steam through the pipe 61 is controlled to determine the rate of concentration of the solution in contact with the specimen. The plug 69 and specimen are substantially cylindrical and the specimen is driven into position to be placed under a static circumferential stress.

The form of the invention shown in Figure 4 provides the same result as in Figure 3, the speci- `men being p laced under circumferential stress vby tightening the nut 84 to force the specimen toward the larger end of the head 8| and thus tend to stretch it. The forms of the device shown in Figures 3 and 4, as in the previous cases, are adapted to be connected to the boiler or other vessel, and the device in'Figure 4 is initially Figure 3, provides a flow of solution past the specimen at a rate slower than the rate of evaporation of the solution in contact with the specimen whereby self-concentration of the solution takes place in contact with, thaspecimen.

From the foregoing it will be apparent that the can carry in contact with a given solution.

present invention provides ajtest bombrfor determining the embrittlement cracking characteristics of boiler Water and other solutions, the testing taking place under conditions closely approximating conditions within the seams, rolled in tube ends or other restricted spaces in the boiler or other vessel. The direct feeding of boiler water to either form-of the device insures the testing under temperature conditions 'approximating those of the boiler, and the slow,

leakage provided through the valves I5 etc. maintain pressure in the device notgreatly below the pressure 'in the boiler or the like, thus likewise closely reproducing pressure conditions .in the boiler during the testing operation. The form of the'device shown in Figure 2 is particularly advantageous for the reason that it provides-stresses or fother methods of manufacture. Applied.

stresses may be createdby any applied load, sta-tic and/or fatigue, etc., or there may be a combination of internal and applied stresses. The essential requirement of the invention, as indicated above, is that the equipment must provide selfevaporation of the solution in contact with the stressed specimen. f

The present invention, therefore, contemplates the reproduction in contact with a stressed specimen of conditions which exist in the boiler or vessel or in restricted spaces therein in which the solution is being employed. More specifically, the'invention contemplates the slow leaking or diffusingA of the solution from the vessel through a constriction, and removing steam or vapor at the low pressure side of the constriction containing a lower concentration of dissolved solid than the entering liquid. In other words, the invention contemplates the maintenance of a slow flow of solution over a test specimen, such flow being at a rate slower than the rate of evaporation on the side of the specimen opposite that through which tlie solution is introduced.' The steam or vapor may be removed under atmospheric pressure or above or below atmospheric pressure.

The various forms of the device illustrated are preferably directly attached to a boiler or other vessel and the forms of the invention shown in ,Figures 1 and 2 will automatically warn the operator when the water becomes dangerous and tends to cause embrittlement cracking. The device is particularly advantageous for use in'determining the amount of a chemical tobe added other end of said another passage at a greater other vessel, of means for testing the embrittleof said passage, means forrsupplying solution to sage, means for supporting and maintaining un- Aother end of said another passage to concentrate cracking characteristics of a solution, compristo boiler water or other /solution to prevent embrittlement cracking. The device also is particularly useful in determining the embrittlement cracking characteristics of any particular steel or metal alloy. Obviously the device will Iallow the determination of the total safe load a given metal 'It is to be understood that the forms of the apparatus illustrated and described are to be taken vas preferred examples of the same, and that various changes in the shape, size and arrangement of parts of the apparatus may be made without departing from the spiritof the invention or the scope of the subioined claims.

We claim:

1. Apparatus for testing the embrittlement cracking characteristics of a solution, comprising,r a body having a passage therein, means for supporting and maintaining under stress a test specimen arranged within and intermediate the ends be tested'to one end of said passage, and means for evaporating solution from the other end of said passage to concentrate the solution in contact with the specimen.

2. Apparatusfor testing the embrittlement cracking characteristics of a solution. comprising a body having a passage therein, means for supporting and maintaining under stress a test specimen arranged within and intermediate the ends of said passage, means for supplying solution to be tested to one end of said passage, means for restricting the ilow of solution from said last named means through said passage, and means for` evaporating solution from the other end of said passage at a rate greater than the rate of ow of the solution to said passage`to concentrate the solution in contact with the specimen.

3. Apparatus for testing the embrittlement cracking characteristics of a solution, comprising means providing one passage for substantially free and continuous circulation of solution from a body of solution to be tested into one end and through said passage and from the other end thereof back to said body of solution to be tested, means providing another passage for receiving solution at one end thereof from said one pasder stress a test specimen arranged within and intermediate the ends of said another passage, and means for evaporating solution from the the solution in contact with the specimen.

4. Apparatus for testing the embrittlement ing means provided one passage for substantially free and continuous circulation of Solution from a body solution to be tested Iinto one end'and through said passage and from the other end thereof back to said body of solution to be tested, means providing another passage for receiving solution at one end thereof from said one passage, means for supporting and maintaining under stress a test specimen arranged within and` intermediate the ends of said another passage, means for restricting the ow of solution from said one passage through .said another passage, and means for evaporating solution from the rate than the rate of flow of solution to said another passage to concentrate the solution in contact with the specimen.

5. The combination with a steam boiler or ment cracking'characteristics of the solution in the vessel, comprising a body having a passage therein, means providing another passage for substantially free and continuous circulation of solution from said vessel to the passage in said body and from the latter passage to said vessel, means for supporting a specimen in the passage