Brittle Failure and /:" . Low-Temperature Welding , c Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 ,;,.'.:-. K. WINTERTON

Head, Welding Section, Physical Metallu1'gy Divisicn, Mines B,'ancl!, Ottawa , 'J

: .'- '., .! .,:, J ABSTRACT INTRODUCTION , :) The causes of brittle failure are explained, and the THERE ARE ALL KINDS OF TROUBLES that can develop aspects of crack propagation and crack initiation treated in equipment in northern climates. These may result separatel)·. The selection of steels for service at low temperatures is considered, and some instances are given from improper selection of materials, unsuitable over­ of special code requirements. General advice is presented all design, inappropriate design or choice of particular for the minimization of the problems of brittle failure. components, manufacturing defects with special sig­ 'Velding in cold weather affects personnel, materials and nificance for operation at low temperatures, etc. equipment. Metallurgieal factors are also involved. as revealed by experimentation and practical experience_ It is not surprising that suitable equipment and Code requirements are explained. Practical advice is materials could in most cases be provided, but that given for overcoming the problems that may be en­ countered. this would entail unwelcome increases in costs. More­ over, in Canad~l at least, the problems have been at­ tacked piecemeal, and there is no systematic ap­ proach available to those who are not immediate!)' deterred by the prospect of paying more for what the}" need. At the University of Alaska, the engineer­ ing faculty places emphasis on special training of, students in the unique aspects of work in the North. Dr. K. \VINTERTON e;raduated in In the U.S.S.R., a more unified approach to northern metallurgy from Binnfngham Uni­ versity in 1940. Subsequently, he problems has been developing, and they are consider­ joined a team working on the welding ing the establishment of a Research Institute for Tech­ of armour steel and was awarded his nical Problems of the North(l). Doctorate in 1943. He joined the Tin Research Institute as a l·esearch met­ The present paper is limited to the consideration allurgist, workinl{ on problems con­ of two aspects of the problem; firstly, brittle frac­ nected with the casting of brass and bronze_ In 1946, he joined the staff of ture, which is certainl}' the most important single ma­ the British Welding Research Asso­ terial problem, and secondl).', the effect of low tem­ ciation, later becoming chief metallur­ peratures on ,,,,'elding-. gist. He emigrated to Canada in 1955 to tal;:e the post of assistant director of the Department ..' of Engineering and Metallurgy of the Ontario Research Foundation. In 1958. he joined the Mines Branch of the BRITTLE FAILURE Department of Ener,gyJ Mines and Resources to take the post of head of the 'Welding Section, Physical Metallurgy Strength and Brittleness Division. On considering the metals used in oil-field opera­ THE PAPER WAE PRESENTED: at the 19th Annual tions, it is apparent that steels are by far the most Technical Meeting of The Petroleum Society of CIM; important. These may be plain-carbon steels or alloy held jointly with the Spring Meeting, Rocky ·Mountain steels, cheap steels or expensive steels, structural District, Division of Production, American Petroleum In­ stitute; Calgary. iVIay, 1968. steels. machinen' steels or special steels. A common characteristic is that they sometimes do not behave as the).' should in cold ·weather.

Technology, January-March, 1969, Montreal 35 ~CoO.--- ~__...,..__.,.._..., In order to consider huw the strength of steel is aff~cted by the cold, it is neces8ary to agree on whnt SRITTlE STPENGr... __~ is meant by stl-ength_ Almost all designs are LJil.:'Ied on yield strength, 01" the load t.hat unit sections will ._-._/ sil~nificantly. Figlll'(~ 1 sustain without deforming -. ISO plots strength against temperature for pure inHl ill \ simple tension, and shows that yield strength actually \ increases as the temperature falls'~l. This may appear to be good, but it has some Lad consequences. At H ­," c.:ertain temperature, the yield stress and fracture \ ~tress ~ 'DO meet; below this temperature, the pure iron " ~SnELD will break sllddenly without deformation. lili:e glass. For pure iron. very low temperature!; are needed ,--.., to achieve this in a simple tensile test'~), as shown in Figure 1. However, there are other factors that can increase the yield stress relative to the fracture stress; '"'--__-::: -::::-_.l.-_-:!-::_---"_~ u ~ompositioll llotche~ <) SO 100 ISO 200 lI. e_g_. anu c.ertain irnpul"ities, and ~1i9 -280 -IBO IOO"F stress ~()nc.entl"ations, and the high speed of loa

plication. Although apparently quite diffel'ent, thesC'Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 Figure J.-Low-Telll]JcrQturc BrittleHel>·.<; in PlIl'e Troll. fac.:turs have the common effect of hindering the duc­ tile deformatiun of steel (slipl. and lead to a prefer­ ence fol' cleavage fractun~ and brittle behaviour. On an atomic scale, dislocation mo\'ement."l al'e inhibited. Taken together, theSe fadors opel'ating in ordinary steels can raise the tempel"atul'es at \...·hich brittleness is encountered to the levels of atmospheric \Iariation. rt might he argued that thi!:'i phenomenon is not of great importance, because. if the design is good, the yield point !:'ihould not be exeeNled. Unfortunately, it i~ possible to have lo\\"·stres~ britlle failure. 01" [ail· ure well below the nominal yield stress.

C1'ack P,"opagafiml Once a brittle cratk is nlIIning, iL requires very little energy to keep it going. There is ample energy stored in a pipeline under high pressure to result in a Fi.rJJtre 2.-F'ailurc in a fLigh-p1·cssun gas pipeline. failure several miles long. as shown in Fi!Jlf,re 2_ Simi­ larly, the residual stresses and service stre8ses in a ship can re­ sult in complete frHcture. breaking it in half. A brittle crack can extend at high speed, in Lhe order of a mile per second. verr often faster than the speed at which the shess which sllstains it ("an relax. In a pipeline, (a) Fracture on ship plate 0.339 in. thick. the cracking speed is faster than the speed of sound in natural gas; that is, fa8tel' than the speed at which a prl~SSUl"e wave can travel in the gas, ~md t.herefore faster than the speed at which the pres­ sure can relax, The speed of sound in oil or in water is much faster than in ail', and if failure occurs when testing with liquid media, the cracks do not travel as far. 'When a brittle crack occurs, it lb) Fracture on ship plate 0.91 ih_ thick_ leaveg behind a trail on the frnc­ hIred 1;urfa,~e, called chevron mark­ ings. as shown in Fir/lire ,9. The apices of the V-shaped marldngs point towal'd the origin of the fail. ure_ This is very cOllvenient for analyzing the sequence of long or complex failures, and in particular f(Jl" locating the probable origin. (c) Fracture produced in laboratory on plate 0.532 in_ thick. Apart from catastrophic failures of the type mentioned, it must be

36 The Journal of Canadian Petroleum obvious that short failures of exactly the same type thought die hard, especially when the alternative is to may' occur which may seriously affect the working spend more money. Not unnaturally, the most strik~ operation of a crane, derrick or other steel fabrication. ing advances have been made in the military and spac·e fields. For rocket casings and nuclear submarine hulls, critical crack sizes are worked out for acceptable ma­ terials. The very searching non-destructive test meth­ C1'ack Initiatian ods are aimed at eliminating flaws excee'ding the size specified for the desired safetJ.~ level. In most practical It is known that once a crack gets started, and work situations, on the other hand, we continue to reaches a critical size. a low stress is sufficient to work with outmoded design methods, with inferior keep it going. There still remains the question of how steels) with indiscriminate good and bad steels, with 'such cracks are initiated. There are several different irrelevant acceptance criteria, and with palliatives ways. Cracks may be present already as the result of rather than cures. faulty welding or mis-handling. Fatigue cracks may Slowly, but inevitably, a change is coming. The rate occur at notches because of repeated or reversed load­ at which it can occur depends more upon the diffusion ing_ However, these extraneous causes are not strictly of widespread knowledge among all those concerned, necessar}~. A notch may be present which raises the and upon the ultimate economic realities, than upon

10caU)~ Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 stress above the yield stress) so that a short any further technical advances. crack may be produced. In addition, the material in the vicinit}~ ma}~ have been previously degraded by There is still not enough quality control of steels straining or strain-ageing. so that its ductility is de­ intended for low-temperature service. A suitable and pleted or exhausted. common test for this purpose is the Charpy-V test. The best way of using the test is to make a number Some actual instances of brittle failure origins may of tests at different temperatures, and then plot a be helpful in illustrating the foregoing remarks. temperature transition curve. At high temperatures, In Canada, one failure started from a \velded cir­ the energy absorbed is considerable; at low tempera­ cular patch on the outside of the pipe which had been tures. the energy absorbed is quite smalL At some installed to repair a leak(~l_ Insufficient heat input critical temperature or, more accurately, over a nar­ was provided, and heat-affected zone cracking oc­ row temperature range, a transition occurs from duc­ CUlTed. In another failure, progressive cracking ex­ tile to hrittle behaviour. The temperature at the 15-ft­ tending from a root-pass heat-affected zone crack was lb energy level is often arbitrarily taken as the transi­ responsible for a severe leak in an oil pipeline. Cracks tion temperature. have often started from mechanical damage to the outer pipe surface - as done, for example. b}~ a bull­ dozer. This damage sometimes results in intense fric­ Experience [1'om Ship Failu.res tion heating, leading to martensite formation and quench cracks. In several cases, cracking has initiated Figun~ 4- illustrates the effect of some of the major from hard-spots. These are circular·areas, about 6 steelmaking variables on brittleness, as indicated by inches in diameter, which have been accidentally the 15-ft-lb Charpy-V transition temperature. quenched from red heat during hot rolling. These mar­ The wartime ship steels are illustrated in the lower tensitic regions can accumulate hydrogen. which e,'en­ left corner of Figure 4. Curve A represents the esti­ tually leads to cracking. mated air temperatures to which the ships were ex­ In welded bridges, brittle failure has sometimes posed, with a peak frequency around 68°F. The small­ caused trouble. An example occurred in the Duplessis er distribution curve, F, represents the range of bridge at Trois Rivieres, Quebec. In more recent times, failure temperatures and shows a peak frequency at the failure of King's Bridge at Melbourne, Australia about 40°F. Block T indicates that most of the ductile was traced to pre-existing heat-affected zone toe brittle transition temperatures fell in the range of cracks in some of the ·welds[·'). A brittle failure also 90° to 30°F. occurred in a small military bridge which had been A careful analysis of ship failures, comparing plates used as a highwal~ bridge in the Yukon. Again, failure in which cracks had initiated with plates through originated from heat-affected zone cracking associat­ \vhich cracks had passed and plates in which cracks ed with some of the welds. had terminated, was very helpful in deciding the de­ It will be noticed that quite frequentl~r mention has sirable level of quality (0). been made of instances of brittle failure initiating The progressive improvement in the post-war from prior heat-affected zone cracks. It will be of grades - A, Band C- is clear_ The adjacent shaded interest to recall this later. in connection with the blocks (Figu1·e 4) sho\v the effect of normalizing. discussion on welding at low temperatures_ However, most improvement being obtained with Grade C, which it must not be thought that faulty welds are the only is a fully-killed steel made to fine-grain practice. Us­ source of trouble. Irregular gas-cuts, badly punched ing these steels, in combination with improved design, " rivet holes, fatigue cracks, quench-cracks, forging ship failures have been reduced to manageable pro­ cracks, un-radiussed ke}~-\vays, sharp corners and portions(7). angles, and many other defects have all been blamed Part of the improvement in ship steels was obtained for initiating brittle failures. It can hardI)' be em­ by modifying the composition. It was found that man­ phasized too much that casual arc strikes or burns are ganese had a beneficial effect. whereas carbon had a very dangerous, from the point of view of initiating harmful effect. As a result of this, more attention was brittle failure<5l. At least one catastrophic ship failure paid to achieving the necessary strength level without was found to have originated in this way. allowing the manganese/carbon ratio to fall to low A position has now been reached where brittle fail­ levels<9l. Impurities such as phosphorus and nitrogen ure could be practically eliminated by the application c.an have a very harmful effect and must be limited. of sound design principles and the development and Of the common alloying metals, apart from mangan­ use of better materials. Old customs and ways of ese, only nickel seems to have a beneficial effect(7).

Technology, January-March, 1969~ Montreal 37 Semi-Killed. Steel fOl' La,nd Cotlsh-u..ctioll ties. Somewhat better is API-5LX-60. not just be­ cause it contains columbium. but because the carbon For non-ship failures, the range of ambient tem­ level is limited and because fine-grain practice is used, peratures will extend to lower values (left of center, FiguTe ~). In one studyIY). failures occurred in the The next three blocks (right of centre. Fig/o·e 4.) thjcknes~ range of +41"F to -4-0"'F, with a peak at -4"F_ The illush-ate the effect of plate fot, a range of transition temperatures of the failed steels varied commercial semi-killed steE'ls made in a Scottish mill'lo,. from O°F to lOO"F, \vith a peak frequency at about 32"F. Structural steel A7 is similar to pre-1948 ship-hull Steel,'): for Low-TcllI1HTutlfre Scrricc steel, and has transition temperatures ranging from A good-qualit~·, unalloyed carbon steel i~ A201 0" to +150"F_ In cold climates there is obviously an (right, Fi,gl/re 4.). This is a silicon-killed sleel with up appreciable risk of brittle failure for bridges. storage to 1 per cent manganese. It can be supplied, under spe­ vessels, etc. made of this steeL The weldable structural cification A300, with guaranteed iii-ft-ib Charm.' key­ steel, .A373. should be a little bettel', with transition hole energy down to -50"F. The best properties can temperatures in the l-ange of -10" to +60"F. only be obtained by normalizing. 01' by the control of Although not illustrated on Figl/'l-e ~, the carbon­ roll-finishing temperature, A203 is a higher strength manganese pipeline steels API-5LX 42, 46. 52 and 56 jJressure-vessel steel, and contain 2 1/; to 3 ~,~ pCI' cent are comparable to A7, and ha,,-e unattractive proper- nickel. depending on grade and thickness (centre. Fin- Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021

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:: ::-- <1~'hlt . -15D1-~ -+-+---+-+----'9'A:-;~2:-;;O'¥;3M;-7;-jl ~-+M-3----1rA-R-r~f-' -:-,-+--_,-:---I:-_-,_---1_1-_-_-+,-_ f----r--+150

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\ r -, - \ I,"I"I', I ! -:- [] T _D I r "1 , I ~'I , L .- A j , , " - .' .,... ~ I ." ...... 50 A'1'"~ .-J [L~ Ci' I - :, sn -, -- - - 'I~ (:':- -: ! 10C __ . I~ '-'-­ I ' IIIAI "M ,. -- NOJ~;S~ill-rl--F-'-;,ljo, I-tE-RllH:'-'-A'Io-l ------l-----+----l ~ IPf" .. _. rAJ t~E~ ::: fr~lI- KI l:"ED ~ 150 L--_'-----'-'...... L------'--.-_--,-_-_-..L----"-_---'------'_--_-----'-_L-----'----_-'------'-_..L----"-_.J;160

Figl/n 4_-Rl>lafil:1! Brittff!l!ess uj T'uJ"iow; Strels.

38 The Journal of Canadian PctrCllcum ure 4). This steel can also be supplied to A300 specifi­ If it is recognized that equipment or construction is cations, with guaranteed 15-ft-lb Gharpy keyhole im­ liable to brittle failure, there is usually not much pact ellergy at temperatures of -75'"F and _150°F. that can be done to minimize the risk of such failure_ A410 (right of center, Figure 4) is a chromium-cop­ Common-sense precautions include the, following: ­ n· : per-nickel-aluminum pressure-vessel steel (about 2 to (a) Avoiding mechanical damage that could provide 3 per cent total alloy content), which can similarly be a notch to trigger a brittle failure_ supplied with guaranteed Gharpy keyhole impact val­ (b) A voiding modifications or repairs that could pro­ ues at temp'eratures down to -150°F_ vide notches or stress-concentration. Weld repairs Typical values for the quenched-and-tempered T-l in particular must be made carefully to preclude steel are given for comparison (right, Figure 4). T-l cracking or poor contour. . -,.", contains a varietJr of additions which total approxi­ (c) Avoiding sudden or impact loading, as this in­ mately 2:LA, per cent alloi~ content. This steel is sup­ creases the danger of crack initiation_ One failure ! • plied in the quenched-and-tempered condition, and it investigated by the Physical Metallurgy Division is only fair to say that the better-known structural resulted from a crane operator tugging at a stop­ steels would also be much improved by full heat­ log gate stuck in ice on the St. Lawrence. :,': treatment. (d) Avoid maximum loading in particularly cold weather. In this connection, it must be pointed

T-l has been followed by many other quenched-and­ Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 tempered steels, and these are being used more and out that if a steel is in the brittle condition, only more for construction. There are many examples of very low loads can be applied with safety_ The probability of the incidence of failure is only '" steel bridges in California deriving maximum benefit ., from the extra strength to be gained from quenched­ loosely related to the magnitude of loading_ ,. and-tempered steels. (e) Consideration might be given in some cases to stress-relieving or heat-treatment that would de­ A353 (top right, Figure 4) is a 9 per cent nickel crease the risk of brittle failure. :..... steel; it can be supplied with a guaranteed 15-ft-Ib (f) Depending upon the design, consideration might Charpy keyhole impact value to temperatures as low be given to improving the regions under peak as -320"F. load by the substitution of better materials or Mention should be made of the Canadian specifica­ components or by the elimination of stress-con­ tion G40.8, which covers three grades of structural centrating factors. steel with improved resistance to brittle failure. All grades have controlled carbon and manganese limits, and the higher grades Band C are made to fine-grain killed-steel practice. On the basis of transition tem­ WELDING IN COLD WEATHER peratures, these grades are good for service tempera­ tures of +25°F, O"F and -25"F respectively. A more complete account of the subject is already oll Summarizing the data available, it may be said that available • there is a limit of about OCF for semi-killed steels. Even with fully-killed steels, it is difficult to go below Personnel about _30 c F without normalizing or eqUivalent treatment; below about _60 c F, it is necessary to use Below about 15"F, cold affects de,:terity, particu­ alloy additions as welL larly in starting and maintaining the arc. Warm cloth­ ing should be worn, but for the hands the best com­ promise seems to be to \vear Jight woC'llen gloves and Cod e Requirements follow a restricted work cycle. The operator should also be sheltered from the wind. Welding helmets rna}' In some specifications, more cognizance is being provide a problem for operators wearing warm head­ taken of the better quality materials already available gear. because of the limited adjustment on existing for service at low temperatures_ Two examples of this headbands_ A more difficult problem is that the helmet will probably suffice. lens may become misty due to condensation_ For these The API Recommended Rules for the Design and reasons, hand-shields may be necessal·y. Construction of Large, Welded Low-Pressure Storage Tanks takes into account the design metal tempera­ Equipment .' ture. For service in the 25 c F to _35 c F range, steels A131, A201 and A442 are required. Sometimes, nor­ For arc welding, an engine-driven motor generator " , , malizing or other special requirements are addition­ ma}~ suffer from the following: - ally specified. (a) The efficiency of a lead-acid battery is reduced Similarly, the GSA Standard Z184, now in draft, at -40c F to a value of 10-25 per cent, depending for the Installation of Gas Transmission and Distri­ upon the current drawn, compared with 100 per bution Piping SJ'stems will require a demonstrated cent at 80"F. Better efficiency, 40 per cent at ability of the pipe metal to perform satisfactorily in -40"F, is obtained with silver-cadmium batter­ the Battelle drop-weight test at the lowest expected ies, but these cost approximately ten times as service temperatures. much as lead-acid batteries. It is customary, therefore, to use lead-acid batteries, maintaining Practical 1l-1ea.sures their efficiency with electrical heaters or by stor­ ing them in a warm place when not in use. The on!}'" sound and effective \vay to avoid brittle (b) Special lubricating oils and greases are required failure is to ensure that appropriate materials are for operation under cold conditions. These must selected for the particular service and that good de­ be of low viscosity and free of waxes and semi­ sign will include the elimination, as far as possible, of solids. Peb-oleum oils or synthetics such as di­ stress-concentration arising from sharp corners, esters, silicones and uncon fluids are used as angles or changes in section. bases in these low-temperature greases.

Technology, January-MarchI 1969, Montreal (c) The volatility of gasoline must be high for win­ part. In one particular case, with ambient tempera­ 1.er starting, and in order to prevent difficulties tures between _50° and -70"F, intersecting craclcs associated with high volatility. such as vapour in the form of a cross were produced as the arc was lock and carburettol'-icing, these fuels must con­ struck; these were usually 8-12 inches long and some­ tain anli-icing compounds. times more. In the 'writer's opinion, the matter of In an)r machinery, a change of fit or tolerance due \veldiug in cold weather should be given careful atten­ to differential construction rna)' cause trouble. For tion in welding Lodes, and the latter should then be example, bronze bearings may seize onto a steel enforced. I11 shaft ). Propel"ly lubricated roller bearings may often It is clear that wind will aggravate the difficulties provide the best answer(ll'. of ,\'elding at low temperatlll'e. In general terms, ef­ The most widely used insulation on welding cable fective welding cannot be carried on with it wind i~ a synthetic t~.. pe of rubber, 5BR, which becomes stiff velocity in excess of 20 mph, and the arc cannot be ill the cold, and even brittle below _45°F. Butyl or maintained at all with wind velocit~l in excess of 30 geoprene would permit more flexibility, but these are mph. \Vind shields and shelters, of variou.s materials non-.standard items, Another possibility might be to and of differing shape and complexity, are often llsed use slightly under-raled cable, so that the heat gen­ for all kinds of field welding. These can var)' from erated would help to maintain flexibility. simply-constrllcted boxes, such as are lIsed for the field welding of pipelines, to quite large complex struc­ Acetylene may be needed for cutting or preheating. tures such a~ that shown in Figlu"e tJ'_ Of course, the Cylinder pressure is very sensitive to temperature, Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 latter was more than a wilHI~hield. [t was

1

Figure 5.-GiTth welding durillg 1Vlllter pipeline con­ Figul'e a,-Heated shelters fOj- 1'cpair wcld­ struction. 1Jlg Of sheU1·e wheels on a iilf lJridge.

40 The Journal of Canadion Petroleum effeCt. The main factors have been confirmed by in­ vestigators ill ·different countries with various weld­ abilitJ.~ tests. In Canada, work has been carried out by the Physical Metallurgy Division, Mines Branch, of the Department of Energy, Mines and Resources. The work was done in a cold room at temperatures in the range of +70° to _GO°F. Figure 7 shows recording equipment outside the cold room. In Belgium, the rela­ tionship \'ifith ambient temperature is relied upon to such an extent that the weldability of a particular steel· is sometimes rated in terms of the lowest tem­ perature at which the steel can be welded without sus­ taining heat-affected-zone cracking. Perhaps of special interest are some tests at the Battelle IVlemorial Institute on simulated joints using API 5LX52 steel, which showed that the percentage of cracked sections through isolated root-pass welds increased from zero at 70°F, to 19 per cent at 55"F, Fi!Jure 7.-Recol·ding equipment {m· cold-~·omn tests. to 34 pel' cent (average) at 40"F and to 37 pel' cent (average) at 20"F_ In complete welds, the extent of Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 cracking could be reduced by minimizing the dela:~r be­ tween the first and second welds, and by completing able comfort. The shelters may be heated, if neces­ the whole joint within a 2-hour period. Preheat or, sary, so that it is easier for the operator to make good­ alternatively. the use of low-hydrogen E7016 electrodes quality welds. was effective in preventing cracking. All of these standards prohibit or tend to prohibit The production of fissures (minute cracks) in as­ w~lding when the primary steel temperature is below deposited ,:...eld-metal is also of interest, because their o"F_ In addition, some specify that the base plate formation is encouraged bJ.~ high cooling rates. Under temperature shall be raised by preheating to a certain favourable conditions, these fissures can link up to minimum value) in the range of 50° to 200°F, if the form major weld cracks. It was found that the num­ plate thickness is above a certain maximum value of ber of fissures increases \'ifith lower deposition tem­ from 1 to 2 inches. peratures, but it appeal·ed that there was a greater Most of the standards require that the starting effect between 70"F and O"F than between O"F and point of welding is to be heated to a temperature U _80°F 2.l. Crack~free welds were obtained at -80"F "warm to the hand" when the primary steel tempera­ with inert-gas metal-arc deposits using consumable ture is in the range of 0" to 32"F_ This requirement : .. electrodes. Low-hydrogen metal-arc electrodes were is presumably based on the idea that the starting point l almost as effectivem. . of the weld is more susceptible to weld difficulties or Many authors have reported on the effect of low defects when the steel is at a temperature below about ambient temperatures on the mechanical properties 32"F. Apparently, it is expected that, once welding is of arc-welded joints. In general, tensile strength and in progress, the heat flow in front of the advancing yield strength are not much affected and, if anything, weld will act in the same way as the local preheat at are increased somewhat. Ductility and impact strength, the start of the weId. This is not correct. Care should hO\vever. were sometimes adversel)' affected. always be taken in preheating to heat a sufficiently large mass of metal along the path of the intended weld to prevent a premature drop in temperature, Code Requirem.ents from that prescribed, before welding is completed_ " Some mention of requirements for welding in cold The standards require greater precautions as the "1 weather. is made in the following U.S. and Canadian plate thickness is increased. This is related, not only ,', Standards: - to the greater heat draw-off from a weld deposit, but ',' (a) Welded Highway and Railway Bridges (A.W.S. D2,O- also to the tendency to slightly higher carbon and/or 63)_ manganese levels in the thicker steel. Presumably, the (b) Welding in Building Construction (A.W.S. Dl.O-63). more rigid requirements for shapes and bars are dic­ c) Field Welding of Storage 'Tanks (A.W.S. D5.1-55). tated by the likelihood that these will have greater ,./ d) Steel Tanks, Standpipes, Reservoirs and Elevated '" l hardenability than will plates_ . ~ : Tanks for 'Vater Storage (A.W.S. D5.2-59 and >:J A_W_W.A- D_100-59). A somewhat different approach is taken in the Ca­ (e) Welded Oil Storege Tanks (A_P_L 12C-195B)_ nadian Standard for Oil Pipe Line Transportation (f) Design and Construction of Large, Welded, Low .-~. Pressure Storage Tanks (A.P.I. 620). Systems. In this case, a drop in ambient temperature ,.:.'.'- (g) A.SJ\LE_ Boiler and Pressure Vessel Code, Sect.ion below 32°F is treated as an essential variable in qual­ VIII - Unfired Pressure Vessels (1959). if:ying \""elding procedures. Welding is not permitted (h) Welding of Bridges, Buildings and i\:[achinety (C.S.A. D W_59-1959) _ at a temperature below 32 F which is lower than that (i) Oil Pipe Line TranstJortation Systems (C.S.A. Z183­ at which the ' .... elding procedm"e has been qualified. " 1967) _ Rather precise directions are given in British Stand­ All of these standards specify, 01' at least recom­ ard Specification RS,2642-1965, General Requirements mend, that no welding shall be done if the welders for the lIIetal-Arc Welding of Medium 'Tensile Weld­ are exposed to inclement conditions. The Canadian able Structural Steel to B_S.968 Type 2_ For butt Standards Association Specification 1V59 requires welds, graphs are provided which show the maximum that, at temperatures below 40"F, the welder and the run lengths to be made with an 18-inch-Iong electrode work are adequately protected against the direct ef­ (this is a convenient way of controlling the minimum fect of wind and snO\v, and that all necessary steps l.veld size) for different combinations of total plate are taken to enable the operator to work in reason- thickness, electrode size and plate temperature. Other

Technology, January-March, 1969, Montreal 41 graphs similarly make it possible to determine the size For ordinary arc welding, an obvious means of pre­ of single-run fillet welds. The S;l!stem of control in­ venting the high cooling rates normally associated corporated in this Standard has been adaptedWl for a with the effect of welding at low temperatures is to new Canadian steel, C.S.A. G40.1Z, which somewhat increase the heat input. For some applications, rough resembles the U.K. steel B.S.968 Type 2. quantitative rules have been dr::twn up for this method of control. Following work done at the BatteHe Memo­ Prudical IIIeasm'es rial Institute, it is now an accepted requirement of the Canadian Standard for Oil Pipe Line Transportation Two practical measures have been found to be use­ Systems that, for field welding, the second pass must ful in overcoming the technical problems associated be started within 5 minutes of completing the first with welding at low temperatures; Le., the use of low­ pass. Somewhat similar is a U.S.S.R. recommendation hJ!drogen electrodes, and proper thermal control. for the welding of pipelines aIHI reservoirs that multi­ Low-h.ydrogen electrodes are generally less liable pu::;s welding should be employed extensivel}r in win­ than other electrodes to heat-affected-zone cracking ter, so that, before l..:ooling down completely, most and weld-metal fissuring. Their obvious advantages '·... elds are reheated by succeeding passes. In manual for low-temperature ,velding are widely recognized welding, no pass longer than 3 feet should be deposit­ and have been demonstrated by numerous investiga­ ed before applying a covering pass; a comparable dis­ tors. Precautions must be taken to keep these elec­ tance for automatic welding would be about 20 ft. hades dn!, as the.y tend to pick up moisture when

Canadian workers have suggested that long weldsDownloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 exposed to the atmosphere. should be made in blocks, so that the intel'pass tem­ Some welding processes, because their rate of energy perature is maintained at a satisfactory leverl~'. From input is high, are inherentl~~ less susceptible to the the same source comes the suggestion that in some effects of low ambient temperatures. These include cases ,velds could be laid on the plate surface just submerged-arc welding, thermit welding, electro-slag outside the welding- groove for preheating purposes welding and enclosed welding. if auxiliary heating services al·e not availablem'. In Canada. and in the colder parts of the United A rule used in the U.S.S.R. i:-; that the specific heat States. the introduction of double-jointing techniques input should be incl"eased by ·1 to 5 per cent (later fll has made it possible for !Jipeline companies to con­ calculations ) suggested thal lhis value should be 7 tinue some aspects of their work during the winter to 8 per cent) for each 18"F drop in temperature be­ months (see Figll1"C S). This method has been used, low normal shop temperatures (apparently in the for example, in trunk lines made from 5LX-52 steel range of 50° to 68"F in the U.S.SR.1- in Manitoba and Alberta, with temperatures regularly A generalized system of weldability control waH around -30"F and occasionally as low as -4B"F. proposed some time ago by Cottrell(l6'. based upon the Double-jointing consists of joining the normal 40-ft use of the Controlled Thermal Severity (C.T,S.) test. lengths to make SO-ft lengths. By this means, 50 per A weldabilit}· index letter from A to G WllS assigned cent of the girth welding can be carried on. when to any particular steel after carr:ying out a prescribed temperatures are low, under conditions rather better schedule of testing, Bradstreeel" later suggested that than are obtainable in the field. Semi-automatic sub­ the wcldability index for the steel could be calculated merged-arc welding is used, with a joint geometr'y ap­ using a formula for carbon-equivalent devised by \Vin­ proaching a dose-butted preparation, necessitating terton II"; _ partial removal of the factory-made bevel on the pipe ends. Large propane burners are used to remove ice lvIn% Nilfr Crf'( and snow from the pipe ends, the heating period re­ C.E. ~ C + --6- + ----w- + -\-0- quired being in the order of half a minute. The high heat input with submerged-arc welding is the main factor responsible for the success of double-jointing.

The carbon-equivalent (C.E.l of the steel may be converted into a weldability index using a table pro­ vided by Bradstreet. In either case. whether the weld­ abilit~· index is determined by test 01' b}r calculation, the "alue can later be substituted in a table to find the minimum plate temperature require.d for any par­ ticular joint, taking into account the electrode diam­ eter and the joint severity (total plate thickness available for heat flow in h-iIL units). The data show, for example, that steel with a weldability index of B can be ",'elded in thicknesses of up to Y:!. in" with elec­ trodes of 6 S.\V.G. or larger (more than O.19Z-in. di­ ameter), at temperatures down to -58"F. For a particular job, limited perhaps to one 01' two steels, working in a certain range of plate thickness, it should not be too difficult to work out proper pro­ cedures, with appropriate thermal control for welding, that would be suitable for the lowest service tempera­ tures expected, although it might be necessar}r to supplement any theoretical studies wi th a test pro­ gram. Under these conditions, it should be possible to continue welding work no matter how low the tem­ FigH/'e 8.-DoulJle-joilltilf!J using submerged-un welding. perature falls.

42 The Journnl of Canadian Pctralcum ~,-'--'-!.. >~- -,

REFERENCES ed from the West of Scotland Iron -& Steel Inst., 60J 224-258, (1952-53). (1) Popov, K. V_, HProblems Relating to Low Tempera­ ( 11) 'Winterton, re., Campbell, W. P.,' and Nolan, I\'I. J., ture Resistance of Technical Equipment in Siberia "Welding of Steel at Low Ambient.T~mperatures,JI and the Far North." P1-oblerny Severa, 9, pp. 121-129, Welding Research Council Bulletin No. 86, (l't'Iarch, (Sept. 1965). 1963). , (2) Parker, E. R., Brittle Behaviou,,- of Ellginefn-ing (12) Agnew, S. A., "Root Bead Welding of Structural Structures, John Wiley & Sons Inc., New York, Steel Restraint Specimens at Low Ambient Tempera­ (1957). tures," Mines Branch Research Report No. PM222, (3) \~linterton. K., "Investigation of Pipeline Failure," Department of .i\'Iines & Resources, OttawaJ (Sept. Mines Branch Investigation Report IR 61-149, De­ 1957) . partment of Mines & Technical Surveys, Ottawa, (13) Girard, L. G., "Weldability of Steels at Low Am­ (March, 1952). bient Temperatures," Physical Metallurgy Division (4) Anon., "Report of the Royal Commission into the Internal Report PM-R-63-41, Department of l\:Iines & Failure of King's Bridge," 6352/63, Victoria, Aus­ Technical Surveys, Ottawa, (Nov_1963). tralia, (1963). (5) Winterton, and Corbett, M. "Dangers of Arc (14) Campbell, W. P., and Winterton, K., "Tentative Ie., J. , Recommendations for the Avoidance of Underhead Strikes and a Possible Remedy," Welding Journal, Cracking when 'Welding Steel Conforming to C.S_A. 39, (3), p. 121" (March, 1960). (6) Acker, H. G., "Review of Welded Ship Failures," Standard G40.12 - General Purpose Structural Welding Research Council Bulletin No. 19, (Nov. Steel," Tran8. Eng. Inst_ Canada, 8, (B-4) , 2-11, 1954) . (Dec. 1965). (7) Anon., "Fourth Technical Px:ogress Report of the (15) Nichols, H. J., "Low Temperature Welding at Downloaded from http://onepetro.org/jcpt/article-pdf/8/01/35/2166420/petsoc-69-01-06.pdf by guest on 30 September 2021 Ship Structure Committee,'J Welding Research Coun­ ChUl'chillJ Manitoba, Winter, 1948-49." Investigation cil BuIletin No_ 55, (Nov. 1959). No. 2537, Department of Mines and Resources, Ot­ (8) Winterton, K., "Selection of Steels for the Avoid­ tawa, (May, 1949). ance of Brittle Failure/, :nnnes Branch Information (16) Cottrell, C. L. 'i\.L, "ControIled Thermal Severity Circular IC 120, Department of i\.'Iines & Technical Cracking Test Simulates Practical Welded Joints," Surveys, Ottawa) (July, 1960). Welding J., 92, (6), 257,-272" (June, 1953). (9) Shank, M. E., "A Critical Survey of Brittle Failure (17) Bradstreet, B. J., "Methods to Establish Procedures in Carbon Plate Steel Structures Other than Ships," for 'Velding Low Alloy Steels," E'nginBer1ng J_, 46, Virelding Research Council Bulletin No. 17, (Jan. 37-41, (Noy. 1963). 1954) . (lB) 'Winterton, K., uWeldability Prediction from Steel (10) MacKenzie, I. 1\01., "Notch Ductility," paper No. 455 Composition to Avoid Heat-Affected Zone Cracking/' ;:. of ConfeTence on B~-ittle Fractnns in Steel, reprint- W.lding J. 40, (6), 253,-258" (June, 1961). --

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Technology. January-March, 1969, Montreal 43