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Note relating to “water-hammer” in steam pipes
JOUI NAL OF
THB
FRANKLIN IN S T I T U TE, OF T I I E STATE OF P E N N S Y L V A N I A ,
FOR T H E PI~OMOT[O~N OF T H E IM:ECHANIC AI~TS. VOL. C X V I .
JUICY, 1883.
:No. 1,
T~I~ Franklin Institute is not responsible for the statements and opinions advanced by contributors to the ,'[OUP~NAI,.
N O T E R L~.I.,.A . I I ~ (~, ~' T()
,,
~, B TA •I•L ~R - H A ~~I M jE R PIPES.
,,
IN STEAM
By P~oL.'. It }~Elrr H. THURSTON. [A paper read betbre the American Society of Mechanical Engineers, Jmle, 1883.]
Tim writer has been called upon during the past winter, in the course of his professional work, to examine into the systems of steam heating in use on so large a scale in New York city, and elsewhere, and to report upon the condition and capabilities of one of those " plants" which have been put in operation. In the com, e of this investigation he was compelled to examine into the peculiar methods of b~jury to which long lines of steam pipe thus used are exposed. The action familiarly known as " w a t e r - h a m m e r " had been long known to him, as to every engineer who has had much to do with steam power, and its singular e[Fccgs had been often observed and commented upon by him, as by others ; but, in this case, these eiIects were developed on so large a scale, and were so serious oftentimes in their conse(luences as to impress upon him the desirability of examining into the matter more carefully than had yet been done. H e has no~ been able to make a systematic ~md thorough investigation, such as he would have liked to make; but he has been able to collect some facts, a few of which will be here presented, that may at least have the effect of calling the attention of engineers more generally to this matter, and may lead to further study of the subject. W~OnE No. VOL.CXVI.--(TmRD SEmF~S,Vol. lxxxvi.) 1
lVttger- Hammer i~, fgteam Pt})es.
[aour. Frank. Inst.,
When a pipe is filled with ste'un, and then has introduced into it a qumltit,y of cold wate U or when a pipe, itself eold, and containing cold water, even in very small quantity, and without pressure, ]ms steam turned into it, the tirst contact of the two fluids is accompanied by a sudden ('ondensation, which e.mses a sharp blow to be struek, usually at the 1}olnt of e,~tranee; and sometimes a sueeession of" such blows o(.eurs, whM~ are the heavier as the pipe is larger, ,~nd w h i d l may be startling, and ,;yen very dangerous. It is ,tot k,~ow,b so tlt," as the writer is aware, precisely how this a(~tion takes place in all eases~ or what eondltions are most fitvorable to the developme,~l of the tremendous pressures which are often produced. Perhal~s the acti,m is as f}~llo\vs : The st(~atn, at entranee~ l)asscs (,ver~ Or ~;:onles in contact with t h e sm'thee of the cold water standing in the pipe. (}ondensation occurs, at ti,'st very slowly, but presently more quiekly, and then so r a p i d l y that the surthee of cont~lel~between the two fluids is broken, and e o n densalion is eOml)leI(~d with a sudde.nness that produces a vacuum. The water surf,rending this \-n(nmm is next l)rojeeted violently f r o m all sides into this va,¢mms .space, and crossing it, strikes upon tim sm'fiwe surr,,mding it. As water is nearly ineompresslb]% the b l o w thus strm'k is like that .t' a solid body~ and the intensi V of the result.ing pressure is th~ greal:er as the distanee through which the p o r t i o n of surfiu'e attacked can yield is less. In this manner enormous p r e s sures are sometimes produe(,d. In s-,m' eases it s(~o,ns certain that sueh pressures may be caused at poims ii~ tt.~ pipe tin" t'r(,m ,tither end, and from the point of e n t r a n c e of the slea,n. For t:xamph., a pipe may lie in a nearly or quite h o r i zontal li,m, and, if not fulh' drained, may contain a considerable quantity ~1' wat(n' l?-ing in the lower portion, whi]e tlie' steam m a y tl~w in al~,we it. The lm~sage ,~t' lids steam along the surihee o f t h e war,q" mav cause some ~islm'lmnce of the surt~me of the liquid, a n d this di~iurlr, tllet! lu,{ng gradually into'eased as the flow of steam beeomres nu,re rapid, may tln:dly ~'m~se a br~ak in the suriltee of the water~ whMl di~tm'b:m(,c may ],,',,du,~. more rapid condensation and still f'urlh,~r agitate the mass, ,mtii eomhms.ltion occurs with such r ' t p i d l t y tlmt a vacuum is t;,rm,.,d :it the point of greatest m.,tion. T h e n e x t result i~ the rushing of swam fi'mn both directions towards this point., e:u'rving with it, :> it go~% massos ~}fwater whieh, coming from o p p o site dire~'ti,ms with enorm,~us vdoeity, meet at the intermediate spot: ag
Jab', lss3.]
l.Vater-tYammcr in Steam Pipes.
3
whMl the condensation has been most rapid, and being stopped by instant collision, produce a pressure which may "only have as its limit the strength of the pipe. Where pipes are not burst by this action, it is common to see them sprung 'rod twisted out of line, torn fi'om their connections, and, when a ~m~cession of shocks occur, as is often the case, the whole line writhes and .}umps lengthwise to an extent that is sufficiently serious to cause well-grounded alarm. The writer had an opportunity, in the course of his work on the ~ase above alluded to, to obtain some probably approximate measures ~f the intensity of this action in long and heavy lines of pipe. :Four lengths of" 8-inch pipe had been split by this action, and the writer desired to ascertain whether tlley remained, in their injured condition, strono- enough to |)era" the or(linar)~ steam pressure of the line from ~vhieh thcy were takcn. This never rose above fifty or sixty pounds per square inch. They were therefore subjected, in a proving-machine, to gradually increased pressures until the already fractured parts were still ]hrthcr injured, the repairs, or rather the pamhing having been carethlly done in such a way that the}, were not strengthened by it. This was done by putting on soft patches along the line of the split and securing them by bolts which were set in the line of the split. The patches thus served as simple stop-valves, preventing the exit of tim water through the break. The following are the results of the tests : Pipe No. 1 . ~ T h i s pipe was split, near one end, for a distance of 15 inches, along the line of the weld. When placed in the provingmachine, it bore the applied pressure until it attained an intensity of 400 pounds per square inch, when the split suddenly extended about ten in(.hes; the pressure could no longer be kept up, and the test terminated. The pipe was then taken to a pipe-cutting machine, and the injured p.art cut off. It was then again subjected to pressure. It bore a pressure of 1,100 pounds per square inch, the highest that it was convenient or customary to apply to that size,~and was taken out sound. Pipe No. 2 . ~ T h i s length was cracked fbr a distance of 15 inches along the line of weld, not far from the middle of its length. The t~raek had opened a little and the £)ipe was slightly bulged. This piece b.~re 300 pounds and then gave way, the fracture extending just enough to let off the pressure.
Water-Itmnmer in St,earn Pipes.
[Jour. Frank. Inst.,
At the opposite end of the pipe was another split, 8 inches in length. The, part just fractured was cut o~I~ and the remaining pot• tlon was again subjected to the, water pressm'e. rl.} I ns• time it bore 1,t)50 pounds per square inch, when the crack was started and ran about 715 inches. It began leaking, and showed plainly the etl~!ct of tit(,, press,m., at about 800 pounds. This was an mmsually intcre;ting specit ran, as the pipe hqd been bulged consid(!ral)ly t)v d m w tt,~l'q u m~( • qhm~ the line of the 8-inch crack. Tim prcssm'e afterward t)(~rne, thcrcibre, seemed to the writer to be likely t() be a thir measure of that; produced originally by the water-hamm(T. Such bulging a.-: was here seen never occurs qt usuaI prcssure~. The new /)reak did not folh)w the wehl, but ran irregularly, and al)l):U'cntly in(liitbrently, through weld or solid iron. I)il)e No. :k---This lcugth was split tbr a distance of' 22 inches, the end (,f the brcal< 1)(~in~ about 3 feet t'l'()lll the end (,f' the pipe. It sustqiued a l)rt,ssm'e . f 250 pounds. The s(mnd part of the pipe was then t(~si(,d up to 1,05t) l)OUnds without injm:y. Iql)c No. 1 . T h i s piece was Sl~tit, like the last, and to just about tit(.' same (.,xtcnt, was t6sted similarly~ and gave way at 300 pounds per s~luarc inch. All of this lfipc was 8-1nch pipe, ~-incil thick, and made with t h e usual t\n'm ()f' hq)-wehted joint. The welds were not always perfect, as is lm)ba/)ly the lh(,t with all such pipe; but this pil)e , butt-welded~ wouh| ~hav('. borne very mu(.h higher pres-qux~s than those to which i t w'~s subjeetod in ordinary work by the steam e'wried on the line. It. cannot be assm'led that these lengths of pipe did not split under pressures less th:m those to which they were at~erward su|4iected b y t h e writer, as it is very possi/)le that the th'st blow may have fbttnd a weal< p'u't of lhe 1@% and the split may, in stone cases, have extended t:o stronger l)m'li(ms. Nevcrth(d(!ss, the writer is inclined to believe t ha{ this was m,t the cqsc in all instances, and is convinced that~ in ond ('ase ",t h:ast--that of tim 8-ind~ (Tack, which was accompanied by decided mlg(, in the l)il~e--the waier ti~?essm.eG at the t est~ wee% a t h,ast al)l)r,.~ximately , v,lual to, and arc Very likely to have exceeded:~ those, obtained at ihe later' test, It seems to him very certain that w e may considvr it as pr(wen that dm pre.~ures produced by " w a t e r [ lmmmer" are often enormously in execs
July, 1883,]
lrxcplorat'ton of Grecrdand.
5
late up.n meeting these tremendous stresses by weight and thickness of metal, but that the engineer must rely principally, if not solely, upon complete and certain drainage of the pipe at all times as the only memos of' satbly handling steam in long pipes, such, especially, as are now coming into u~e in the heating of cities by steam led through the streets in m~dergr(,md mains. The thets here presented have been, to the writer, something of a revclatlon, and have seemed to him to possess mmsual in,terest and importance to the engineer using stemn m~der such conditions as are here refl, rred to. It is a ~,lct which has long been well known, ~hat these suddenly produced pressures are often very great. The writer has occasionally, C,,' many years, l
THB
FRANKLIN IN S T I T U TE, OF T I I E STATE OF P E N N S Y L V A N I A ,
FOR T H E PI~OMOT[O~N OF T H E IM:ECHANIC AI~TS. VOL. C X V I .
JUICY, 1883.
:No. 1,
T~I~ Franklin Institute is not responsible for the statements and opinions advanced by contributors to the ,'[OUP~NAI,.
N O T E R L~.I.,.A . I I ~ (~, ~' T()
,,
~, B TA •I•L ~R - H A ~~I M jE R PIPES.
,,
IN STEAM
By P~oL.'. It }~Elrr H. THURSTON. [A paper read betbre the American Society of Mechanical Engineers, Jmle, 1883.]
Tim writer has been called upon during the past winter, in the course of his professional work, to examine into the systems of steam heating in use on so large a scale in New York city, and elsewhere, and to report upon the condition and capabilities of one of those " plants" which have been put in operation. In the com, e of this investigation he was compelled to examine into the peculiar methods of b~jury to which long lines of steam pipe thus used are exposed. The action familiarly known as " w a t e r - h a m m e r " had been long known to him, as to every engineer who has had much to do with steam power, and its singular e[Fccgs had been often observed and commented upon by him, as by others ; but, in this case, these eiIects were developed on so large a scale, and were so serious oftentimes in their conse(luences as to impress upon him the desirability of examining into the matter more carefully than had yet been done. H e has no~ been able to make a systematic ~md thorough investigation, such as he would have liked to make; but he has been able to collect some facts, a few of which will be here presented, that may at least have the effect of calling the attention of engineers more generally to this matter, and may lead to further study of the subject. W~OnE No. VOL.CXVI.--(TmRD SEmF~S,Vol. lxxxvi.) 1
lVttger- Hammer i~, fgteam Pt})es.
[aour. Frank. Inst.,
When a pipe is filled with ste'un, and then has introduced into it a qumltit,y of cold wate U or when a pipe, itself eold, and containing cold water, even in very small quantity, and without pressure, ]ms steam turned into it, the tirst contact of the two fluids is accompanied by a sudden ('ondensation, which e.mses a sharp blow to be struek, usually at the 1}olnt of e,~tranee; and sometimes a sueeession of" such blows o(.eurs, whM~ are the heavier as the pipe is larger, ,~nd w h i d l may be startling, and ,;yen very dangerous. It is ,tot k,~ow,b so tlt," as the writer is aware, precisely how this a(~tion takes place in all eases~ or what eondltions are most fitvorable to the developme,~l of the tremendous pressures which are often produced. Perhal~s the acti,m is as f}~llo\vs : The st(~atn, at entranee~ l)asscs (,ver~ Or ~;:onles in contact with t h e sm'thee of the cold water standing in the pipe. (}ondensation occurs, at ti,'st very slowly, but presently more quiekly, and then so r a p i d l y that the surthee of cont~lel~between the two fluids is broken, and e o n densalion is eOml)leI(~d with a sudde.nness that produces a vacuum. The water surf,rending this \-n(nmm is next l)rojeeted violently f r o m all sides into this va,¢mms .space, and crossing it, strikes upon tim sm'fiwe surr,,mding it. As water is nearly ineompresslb]% the b l o w thus strm'k is like that .t' a solid body~ and the intensi V of the result.ing pressure is th~ greal:er as the distanee through which the p o r t i o n of surfiu'e attacked can yield is less. In this manner enormous p r e s sures are sometimes produe(,d. In s-,m' eases it s(~o,ns certain that sueh pressures may be caused at poims ii~ tt.~ pipe tin" t'r(,m ,tither end, and from the point of e n t r a n c e of the slea,n. For t:xamph., a pipe may lie in a nearly or quite h o r i zontal li,m, and, if not fulh' drained, may contain a considerable quantity ~1' wat(n' l?-ing in the lower portion, whi]e tlie' steam m a y tl~w in al~,we it. The lm~sage ,~t' lids steam along the surihee o f t h e war,q" mav cause some ~islm'lmnce of the surt~me of the liquid, a n d this di~iurlr, tllet! lu,{ng gradually into'eased as the flow of steam beeomres nu,re rapid, may tln:dly ~'m~se a br~ak in the suriltee of the water~ whMl di~tm'b:m(,c may ],,',,du,~. more rapid condensation and still f'urlh,~r agitate the mass, ,mtii eomhms.ltion occurs with such r ' t p i d l t y tlmt a vacuum is t;,rm,.,d :it the point of greatest m.,tion. T h e n e x t result i~ the rushing of swam fi'mn both directions towards this point., e:u'rving with it, :> it go~% massos ~}fwater whieh, coming from o p p o site dire~'ti,ms with enorm,~us vdoeity, meet at the intermediate spot: ag
Jab', lss3.]
l.Vater-tYammcr in Steam Pipes.
3
whMl the condensation has been most rapid, and being stopped by instant collision, produce a pressure which may "only have as its limit the strength of the pipe. Where pipes are not burst by this action, it is common to see them sprung 'rod twisted out of line, torn fi'om their connections, and, when a ~m~cession of shocks occur, as is often the case, the whole line writhes and .}umps lengthwise to an extent that is sufficiently serious to cause well-grounded alarm. The writer had an opportunity, in the course of his work on the ~ase above alluded to, to obtain some probably approximate measures ~f the intensity of this action in long and heavy lines of pipe. :Four lengths of" 8-inch pipe had been split by this action, and the writer desired to ascertain whether tlley remained, in their injured condition, strono- enough to |)era" the or(linar)~ steam pressure of the line from ~vhieh thcy were takcn. This never rose above fifty or sixty pounds per square inch. They were therefore subjected, in a proving-machine, to gradually increased pressures until the already fractured parts were still ]hrthcr injured, the repairs, or rather the pamhing having been carethlly done in such a way that the}, were not strengthened by it. This was done by putting on soft patches along the line of the split and securing them by bolts which were set in the line of the split. The patches thus served as simple stop-valves, preventing the exit of tim water through the break. The following are the results of the tests : Pipe No. 1 . ~ T h i s pipe was split, near one end, for a distance of 15 inches, along the line of the weld. When placed in the provingmachine, it bore the applied pressure until it attained an intensity of 400 pounds per square inch, when the split suddenly extended about ten in(.hes; the pressure could no longer be kept up, and the test terminated. The pipe was then taken to a pipe-cutting machine, and the injured p.art cut off. It was then again subjected to pressure. It bore a pressure of 1,100 pounds per square inch, the highest that it was convenient or customary to apply to that size,~and was taken out sound. Pipe No. 2 . ~ T h i s length was cracked fbr a distance of 15 inches along the line of weld, not far from the middle of its length. The t~raek had opened a little and the £)ipe was slightly bulged. This piece b.~re 300 pounds and then gave way, the fracture extending just enough to let off the pressure.
Water-Itmnmer in St,earn Pipes.
[Jour. Frank. Inst.,
At the opposite end of the pipe was another split, 8 inches in length. The, part just fractured was cut o~I~ and the remaining pot• tlon was again subjected to the, water pressm'e. rl.} I ns• time it bore 1,t)50 pounds per square inch, when the crack was started and ran about 715 inches. It began leaking, and showed plainly the etl~!ct of tit(,, press,m., at about 800 pounds. This was an mmsually intcre;ting specit ran, as the pipe hqd been bulged consid(!ral)ly t)v d m w tt,~l'q u m~( • qhm~ the line of the 8-inch crack. Tim prcssm'e afterward t)(~rne, thcrcibre, seemed to the writer to be likely t() be a thir measure of that; produced originally by the water-hamm(T. Such bulging a.-: was here seen never occurs qt usuaI prcssure~. The new /)reak did not folh)w the wehl, but ran irregularly, and al)l):U'cntly in(liitbrently, through weld or solid iron. I)il)e No. :k---This lcugth was split tbr a distance of' 22 inches, the end (,f the brcal< 1)(~in~ about 3 feet t'l'()lll the end (,f' the pipe. It sustqiued a l)rt,ssm'e . f 250 pounds. The s(mnd part of the pipe was then t(~si(,d up to 1,05t) l)OUnds without injm:y. Iql)c No. 1 . T h i s piece was Sl~tit, like the last, and to just about tit(.' same (.,xtcnt, was t6sted similarly~ and gave way at 300 pounds per s~luarc inch. All of this lfipc was 8-1nch pipe, ~-incil thick, and made with t h e usual t\n'm ()f' hq)-wehted joint. The welds were not always perfect, as is lm)ba/)ly the lh(,t with all such pipe; but this pil)e , butt-welded~ wouh| ~hav('. borne very mu(.h higher pres-qux~s than those to which i t w'~s subjeetod in ordinary work by the steam e'wried on the line. It. cannot be assm'led that these lengths of pipe did not split under pressures less th:m those to which they were at~erward su|4iected b y t h e writer, as it is very possi/)le that the th'st blow may have fbttnd a weal< p'u't of lhe 1@% and the split may, in stone cases, have extended t:o stronger l)m'li(ms. Nevcrth(d(!ss, the writer is inclined to believe t ha{ this was m,t the cqsc in all instances, and is convinced that~ in ond ('ase ",t h:ast--that of tim 8-ind~ (Tack, which was accompanied by decided mlg(, in the l)il~e--the waier ti~?essm.eG at the t est~ wee% a t h,ast al)l)r,.~ximately , v,lual to, and arc Very likely to have exceeded:~ those, obtained at ihe later' test, It seems to him very certain that w e may considvr it as pr(wen that dm pre.~ures produced by " w a t e r [ lmmmer" are often enormously in execs
July, 1883,]
lrxcplorat'ton of Grecrdand.
5
late up.n meeting these tremendous stresses by weight and thickness of metal, but that the engineer must rely principally, if not solely, upon complete and certain drainage of the pipe at all times as the only memos of' satbly handling steam in long pipes, such, especially, as are now coming into u~e in the heating of cities by steam led through the streets in m~dergr(,md mains. The thets here presented have been, to the writer, something of a revclatlon, and have seemed to him to possess mmsual in,terest and importance to the engineer using stemn m~der such conditions as are here refl, rred to. It is a ~,lct which has long been well known, ~hat these suddenly produced pressures are often very great. The writer has occasionally, C,,' many years, l