56 Pipeline Rules of Thumb Handbook however, by use of Young’s Modulus of Elasticity (E = stress over strain). The new pipe length can be calculated from the formula: where q = sin -1 X/R A comparison of the new pipe length with the original pipe length will result in a figure for strain as a result of the new profile. Knowing the strain, additional longitudinal stress can be easily calculated. So the pipeline was actually stretched 0.19 ft or 2.28 in. This is well within the 35,000-psi yield strength of Grade B pipe. Source Pipe Line Industry, July 1986. Strain LL E Stress Strain so longitudinal stress E Strain or LS psi = = - ( ) = = = ¥ = ¥ ¥ = D 750 19 750 00 750 00 0 000253 29 10 0 000253 7 347 6 . . . . , . , . In Example ft ft Arc length AL ft ft Length of new line AL ft 1 175 4 350 2 3056 4 350 2 3056 180 175 047 4 50 750 19 1 , sin , . , . . . q p = = ∞ ( ) = ( ) ∞ ( ) = = ( ) + = - Arc Length R = p q 180 • Move convoy of sidebooms 250 ft, lift the line, remove 6-in. block at beginning and end supports and 12 in. of blocks at inner supports. • Repeat until total transition length is lowered 12 in., except for several end supports, which are lowered less than 6 in. to match required deflections. Then come back and do it again, repeating several times until the pipeline is completely lowered. Note that each repeat becomes shorter. Check final pipeline elevations if desired. • Check tape wrap for possible damage, add 12 in. of sand or pre-mix around pipe, backfill and compact. Surprisingly, this operation goes very quickly, but must be well coordinated. One person should signal the sideboom operators to lower the pipeline concurrently, so as to elimi- nate excessive bends and sags. The pipeline is heavy when full of liquid, and if not handled carefully, it could easily rupture. Pressure should be reduced, and extreme caution exercised during the actual lowering process. Strain calculations A new profile means the pipeline has been stretched a certain amount, assuming line was horizontal originally. (If the pipeline was convex, lowering it will put the steel into com- pression.) Fortunately, steel is very forgiving either way, and the added strain is generally not a problem. It can be checked, WELDING When should steel be preheated before welding? It is not necessary to preheat this particular steel before welding it. But for another example: This steel should be preheated, particularly for early morning welding. Why does preheating prevent cracking? It slows the cooling rate and reduces the amount of austenite retained as the weld cools. This prevents microcracking. Other alloying elements and pipe wall thickness may also influence when joints of high strength pipe should be preheated. Carbon Equivalent = + = . . . 20 1 60 4 0 60 Carbon Manganese = = 0 20 1 60 . . From the chemistry of the steel determine the carbon equivalent: If it exceeds 0.58 the steel may be crack sensitive and should be preheated before welding in ambient temperatures below 40°F. Example. If steel pipe having a carbon content of 0.25 and manganese content of 0.70 is to be welded in springtime tem- peratures, ranging from 40°F to 80°F, is preheat necessary? Carbon Equivalent = + = + = . . . . . 25 70 4 25 175 0 425 Carbon Equivalent C Mn = + 4
Transcript
56 Pipeline Rules of Thumb Handbook
however, by use of Young’s Modulus of Elasticity (E = stressover strain).
The new pipe length can be calculated from the formula:
where q = sin-1 X/RA comparison of the new pipe length with the original pipe
length will result in a figure for strain as a result of the newprofile. Knowing the strain, additional longitudinal stress canbe easily calculated.
So the pipeline was actually stretched 0.19 ft or 2.28 in.
This is well within the 35,000-psi yield strength of GradeB pipe.
Source
Pipe Line Industry, July 1986.
Strain L LE Stress Strain so longitudinal stress E Strain or
LS psi
= = -( ) == = ¥= ¥ ¥ =
D 750 19 750 00 750 00 0 000253
29 10 0 000253 7 3476
. . . .,
. , .
In Example ft ftArc length AL ft ftLength of new line AL ft
• Move convoy of sidebooms 250 ft, lift the line, remove 6-in. block at beginning and end supports and 12 in. ofblocks at inner supports.
• Repeat until total transition length is lowered 12 in.,except for several end supports, which are lowered lessthan 6 in. to match required deflections. Then come back and do it again, repeating several times until thepipeline is completely lowered. Note that each repeatbecomes shorter. Check final pipeline elevations ifdesired.
• Check tape wrap for possible damage, add 12 in. of sandor pre-mix around pipe, backfill and compact.
Surprisingly, this operation goes very quickly, but must bewell coordinated. One person should signal the sideboomoperators to lower the pipeline concurrently, so as to elimi-nate excessive bends and sags. The pipeline is heavy when fullof liquid, and if not handled carefully, it could easily rupture.Pressure should be reduced, and extreme caution exercisedduring the actual lowering process.
Strain calculations
A new profile means the pipeline has been stretched acertain amount, assuming line was horizontal originally. (If thepipeline was convex, lowering it will put the steel into com-pression.) Fortunately, steel is very forgiving either way, andthe added strain is generally not a problem. It can be checked,
WELDING
When should steel be preheated before welding?
It is not necessary to preheat this particular steel beforewelding it.
But for another example:
This steel should be preheated, particularly for earlymorning welding.
Why does preheating prevent cracking? It slows the coolingrate and reduces the amount of austenite retained as the weldcools. This prevents microcracking. Other alloying elementsand pipe wall thickness may also influence when joints of highstrength pipe should be preheated.
Carbon Equivalent = + =.
..20
1 604
0 60
CarbonManganese
==
0 201 60
..
From the chemistry of the steel determine the carbonequivalent:
If it exceeds 0.58 the steel may be crack sensitive andshould be preheated before welding in ambient temperaturesbelow 40°F.
Example. If steel pipe having a carbon content of 0.25 andmanganese content of 0.70 is to be welded in springtime tem-peratures, ranging from 40°F to 80°F, is preheat necessary?
Carbon Equivalent = + = + =.
.. . .25
704
25 175 0 425
Carbon Equivalent C
Mn= +
4
Construction 57
Welding and brazing temperatures
Carbon Steel Welding 2700–2790°FStainless Steel Welding 2490–2730°FCast Iron Welding 1920–2500°FCopper Welding and Brazing 1980°FBrazing Copper-Silicon with Phosphor-Bronze 1850–1900°FBrazing Naval Bronze with Manganese Bronze 1600–1700°FSilver Solder 1175–1600°FLow Temperature Brazing 1175–1530°FSoft Solder 200–730°FWrought Iron 2700–2750°F
Reprinted with Permission—Tube Turns, Inc.
Mechanical properties of pipe welding rods
When welded and tested in accordance with appropriate AWS or MIL specifications(1)
(1) Mechanical properties obtained with each type electrode also depend uponchemistry of the pipewelding procedures andthe rate of cooling.
Since these factors vary between actual applications and testing conditions, the mechanical properties may also vary.
Reprinted with Permission—Lincoln Electric Co.
Electrode AWS Class Tensile psi Yield psi %Elong. in 2≤ Tensile psi Yield psi %Elong. in 2≤
Shielded Metal-Arc Welding3/16, 7/32, 1/4 inch electrodes 125/16, 3/8 inch electrodes 14
Atomic Hydrogen Welding 10 to 14
Carbon-Arc Welding 14
Operation Shade No.
Soldering 2
Torch Brazing 3 or 4
Oxygen Cuttingup to 1 inch 3 or 41 to 6 inches 4 or 56 inches and over 5 or 6
Gas Weldingup to 1/8 inch 4 or 51/8 to 1/2 inch 5 or 61/2 inch and over 6 or 8
Shielded Metal-Arc Welding1/16, 3/32, 1/8, 5/32 inch electrodes 10
PIPELINE WELDING
Meeting Today’s Quality Requirements For Manual Vertical Down Techniques
years ago. Therefore, it will take a change in the attitude ofthe welders and everyone else involved if this new level ofquality and workmanship is to be met. In turn, a commitmentto new methods, equipment and theory will be required byall concerned.
Importance of joint preparation
It must be recognized that all joint preparation details(Figure 6) are critical and any variation could directly con-tribute to rejected welds.
Without good cooperation from those who prepare the pipeedges and the line-up crew, the welder has very little chanceof meeting today’s rigid inspection requirements. Too oftenthe attitude exists that variations in fit-up and joint prepara-tion are permissible and that the welder can compensate forthem. This attitude cannot be tolerated. It puts too muchresponsibility on the welder and inevitably leads to rejects.
Recommended procedures for properly cleaning pipe
For lowest cost and highest quality, careful attention to thecleaning of pipe joint surfaces is critically important. Today’s
Pipelines are inspected more critically than ever before and today’s radiographic equipment and techniques produceclearer radiographs with greater sensitivity than in the past.Although codes have not changed drastically, interpretationstandards have been upgraded. The combination of more rigorous inspection, better testing methods, and high accept-ability standards often approaches an attitude requiring zerodefects.
This poses some serious problems because the job ofwelding cross-country pipelines under typical conditions hasalways been an extreme challenge requiring specialized andhighly developed skills. Now that the demands are greater,even the best welding operators are having trouble.Rejectable defects usually require cutting out the entire weld.This is expensive and can cost competent pipeline welderstheir jobs.
The purpose of this bulletin is to discuss some of the morecommon reasons given for rejecting a pipeweld and to suggestwhat may be done to correct some of these conditions.
Change in attitude
Any discussion on this subject should begin by acceptingthe fact that the standards are higher than they were a few
Reprinted with permission—Tube Turns, Inc.
Construction 59
Internal undercut
See Figures 1 through 5 for x-rays of the various defectsthat can cause rejects. Of these, one of the most common andtroublesome is internal undercut (undercut on the inside ofthe pipe). This is understandable because it occurs on the“blind side” and the operator cannot see it happening. Con-sequently, he cannot immediately do anything to correct it.To make matters worse, he seldom gets a chance to see thex-ray negative or the actual weld itself. All of this makes it difficult for him to correct the situation.
Undercut may be the direct result of poor joint prepara-tion or fit-up. If the joint does not conform to the details spec-ified in the established procedures (see Figure 6), everyreasonable effort should be made to correct it before startingto weld.
Internal undercut will tend to occur if:1. The root face (Land) is too small.2. The root opening is too large.3. If a severe high-low condition exists.4. The current is too high.
When any undesirable variation occurs in the joint prepara-tion, the normal reaction is to compensate for it by juggling
pipe welders face pipe which may be covered with a varietyof coatings; these include primers, epoxy, tar, paper, varnish,rust, scale or moisture.
While joint cleanliness is important in all welding, it is espe-cially so in the root pass of pipe. Even a thin film of contam-inants, which may be difficult to see with the naked eye, maybe present. Failure to recognize and properly clean joints canresult in a hollow bead or other welding defects.
Follow these instructions to minimize costly defects:
1. Remove all moisture and condensations of any typeprior to welding. The joint must be completely dry.
2. Clean BOTH ends of the pipe INSIDE AND OUT toremove traces of paint, rust, scale, oil, epoxy, or organicmaterials. The area to be cleaned should extend at least 1 inch (25mm) from the end of the bevel (perANSI/AWS D10.11-80 Page 1) on both the INSIDE andOUTSIDE surfaces.
3. A recommended method for cleaning in the field asdescribed above is the use of a heavy duty straight shaftgrinder with a rubber expanding wheel and a carbidecoated sleeve. The small shaft and reduced overallweight allows easy access to the inside and outside sur-faces of the pipe.
Courtesy of Pipeline & Gas Industry.
60 Pipeline Rules of Thumb Handbook
Figure 1. Radiographs of internalundercut. This defect may be intermit-tent or continuous (Figure 2) and eitheron one side or both sides of the weldcenterline.
WHEN RADIOGRAPHS ARE INDICATIVE OF POOR WORKMANSHIP, BEST RESULTS CAN BE OBTAINED BY SHOWING THERADIOGRAPHS TO THE WELDER SO THAT HE CAN UNDERSTAND WHAT HE IS DOING WRONG AND CORRECT IT.
Figure 2. Radiographs of internalundercut and the lack of penetrationwhich tends to occur at a stop and start.
Figure 3. Radiographs of lack of pen-etration on the stringer bead appearsas a single, straight dark line.
Figure 4. Radiographs of unfilledwagon tracks. Distinguishing betweenthis defect and internal undercut re-quires skill and experience.
Construction 61
A skillful line-up crew can be helpful in juggling the rootspacing to bring about the most favorable results, but this haslimitations. And it is at best a poor substitute for a uniformand consistent joint preparation.
Internal chamfer
It is important to remove any burr or overhang on theinside edge of the pipe after the root face has been machined
the root spacing. Within limits, this can be fairly effective. Forexample:
Figure 5. Radiographs of porosity.
Condition Change in Root Spacing
Land too small. Decrease root spacing.Land too large. Increase root spacing.High-low condition. Decrease root spacing.Bevel too small. Increase root spacing.
Figure 6. Recommended joint preparation andtypical procedures—operate within these toler-ances to help ensure good quality welds.
62 Pipeline Rules of Thumb Handbook
Assuming that the joint preparation is correct, the keyholesize is a function of current, electrode angle and pressure. Thecurrent should be “fine tuned” to produce a small keyholewhen the electrode is dragged lightly using the normal elec-trode angle. If minor variations occur in the keyhole size (forany reason), the electrode angle and pressure can be manip-ulated to maintain the proper keyhole size (Figure 9).
In general, a keyhole which is about 1/8≤ (3.2mm) in lengthis ideal; if it becomes 5/32≤ (4.0mm) or longer, undercut andwindows are imminent.
Frequently, a good inside bead is obtained without havinga visible keyhole. For example, at a tight spot, the keyholemay disappear and the arc goes “inside the pipe.” With theproper manipulative skill, this condition is tolerable and agood inside bead will be obtained. But, when it is done in thismanner, the welder is largely dependent on the sound of thearc inside the pipe. A small, visible keyhole is easier to workwith and is a much more controllable condition.
Significance of arc voltage
It is recommended that meters be used since a fairly goodcorrelation can be established between the arc voltage andthe keyhole size. For example, under controlled conditions,an ideal keyhole size is consistently accompanied by an arcvoltage of no more than 25 volts. When keyhole size is
(or ground). However, this clean-up operation should neverproduce an internal chamfer. A condition such as this isalmost certain to result in “internal undercut” (Figure 7). SeeRecommended Procedures for Cleaning Pipe on the previouspage.
Undercut vs. welding current
Excessive current produces internal undercut. Further, theincidence of internal undercut is more prevalent in the 4-6-8o’clock portions of the pipe. In this bottom area it is possibleto use a considerably higher current than is necessary withoutgetting burn-through, and this results in overheating andundercutting. Knowing this, it would appear to be a simplematter to specify an ideal current which would not giveundercut. However, this is extremely difficult because of themany variables of the many interrelated factors.
A recommended current range is given in Figure 6, but itis necessarily rather broad to cover all reasonable variations.From a practical standpoint, the correct current should bedetermined by starting within the recommended range andthen “fine tuning” to get precisely what “feels good” and pro-duces the required results. This final current value will varyslightly from one operator to another and with different pipematerials, diameters, wall thickness, etc.
Because of inaccuracies in ammeters, the effect of arcvoltage on current, the inability to accurately read a bobbingammeter, etc., it is impractical to hold to an arbitrary currentvalue. For the accomplished stringer bead welder, the selec-tion of the ideal current is not too difficult—but he will bedoing it primarily by “feel and touch.”
Keyhole size vs. current and undercut
To get a good inside bead it is highly desirable to maintaina small, visible keyhole at all times. If the keyhole is allowedto get too big, it will result in internal undercut and/orwindows (Figure 8).
Figure 7. An internal chamfer will tend to leave an unfilled areaon one or both sides of the stringer bead. On the x-ray this willbe interpreted as internal undercut.
Figure 8. Maintaining a small keyhole will help assure a good inside bead. The larger keyhole at the right is almost certain to giveinternal undercut and/or windows.
Construction 63
Figure 9). In an extreme case, a second pair of hands may be required to adjust the current up or down on a signal fromthe welder. This requires a good communication system anda well-coordinated effort to avoid overshooting or under-shooting the current. In some cases, this becomes a survivaltechnique to make up for other undesirable variations.
Undercut—real or imaginary?
If visual inspection were practical for determining internalundercut, it would be easy to accurately determine its pres-ence and severity. However, this is not the case. Radiographyis the judge of internal conditions and this has led to manyquestionable interpretations. If internal undercut is present,it will show up on the film as a very narrow, dark line imme-diately adjacent to the stringer bead—on one or both sides.The darkness of the line will vary with the depth of the under-cut (Figures 1 and 2).
Proper identification of undercut is sometimes difficultbecause its location is directly in line with the “wagon track”area (Figure 4). Distinguishing one from the other may bedifficult.
Correct interpretation of internal undercut may be furthercomplicated by the fact that a “stout” inside bead will standout clearly (lighter on the film) against the adjacent areawhich is thinner and therefore darker. The thinner, darkerarea will be further darkened by the presence of any fairlydeep widely spaced surface ripples in the cap pass. The neteffect is to produce a dark shading in the area where internalundercut might occur.
increased by increasing current, increasing the gap, changingthe electrode angle, etc., the arc voltage increases to 26–28volts. This is reasonable because the arc voltage reflects arclength. At the higher arc voltages, internal undercut andwagon tracks may occur.
The same arc voltage numbers quoted above may not occurin all instances. However, it is readily apparent that there is adependable correlation between keyhole size and arc voltage.A maximum tolerable arc voltage can be determined byexperimentation.
It should be further noted that this arc voltage is deter-mined while welding and it should not be confused with theopen circuit voltage. Also, it can be affected by the weldingtechnique; changes in electrode angles and drag techniquesshould not be allowed to cloud the issue.
Varying current/varying gap
Greater root penetration naturally occurs at the top andbottom portions of the pipe and least penetration tends tooccur at the sides. This being the case, it would be desirableto alter the root spacing accordingly but this obviously is notpractical. It should also be noted that a condition whichpermits maximum spacing on top and bottom and minimumspacing on the sides is not tolerable.
Assuming a uniform gap all the way around, the ideal con-dition would be to vary the current as the weld progressesfrom 12 to 6 o’clock to compensate for the changes in pene-tration due to position. Instead, penetration changes areusually controlled by the manipulative skills of the welder (see
ONE OF THE PRIME OBJECTIVES OF THE STRINGER BEAD CREW SHOULD BE TO PROVIDE A GOOD,STOUT STRINGER WITH AS MUCH THROAT AS POSSIBLE.
Figure 9. The penetration and keyhole size can be effectively controlled by varying the electrode angle as shown—if the joint preparation is uniform.
64 Pipeline Rules of Thumb Handbook
It is the responsibility of the stringer bead crew to mini-mize wagon tracks and the responsibility of the hot pass crewto burn them out. This is normally done with 5/32≤ (4.0mm)electrode at about 175–180amps. The secret in melting outwagon tracks lies primarily in the skill of the hot pass crewand the penetration factor of the electrode. The majority ofthe hot pass men use a rapid stitching technique whichexposes the wagon track momentarily and permits them todirect the arc into the undercut area and melt them out.
The depth of the wagon tracks may be affected by the following:
Although this darker area is considerably wider than anyundercut, it has been mistaken for undercut and resulted incutting out good welds. Normally, a “stout” inside bead is con-sidered good, but in this instance, the stouter the bead, thedarker the adjacent area would appear (Figure 10).
Wagon tracks
It is not possible to completely eliminate the sidewallundercut produced by the stringer bead. This condition isgenerally referred to as “wagon tracks” (Figures 4 and 11).
Figure 10. Any deep surface ripples located directly above apoint adjacent to the inside bead will contribute to a darkshading of the film at this area. This has been misinterpreted bysome as internal undercut.
Figure 11. “Wagon tracks” are located on either side of thestringer bead.
Condition Results
Bevel too small (Figure 12). Increases depth of W.T.Root Spacing (Gap) too small. Increases depth of W.T.Current and/or speed too high. Increases depth of W.T.
In extremes, it may be necessary to use a grinder to open upthe sidewalls to minimize deep “wagon tracks” or, if they dooccur, to grind the stringer to eliminate the high peakedcenter (Figure 13). In all cases a 5/32≤ (4.0mm) thickness discgrinder should be used to grind root beads on all pipe from12≤ (304.8mm) up irrespective of wall thickness [a 1/8≤(3.2mm) disc grinder will grind the center and roll the sidesover on the wagon track unless side pressure is applied]. Thiswill make it easier to melt them out.
If the stringer bead tends to wander to one side or theother, it will leave a deep undercut on the shallow side. Thiscondition should be corrected immediately by changing theelectrode angle (Figure 14).
Figure 12. The depth of the wagon tracks will vary inversely with the bevel angle.
Figure 13. A disc grinder, if used with restraint, can be helpful in correcting the condition shown above.
Construction 65
The hollow bead
The stringer bead defect shown in this sketch is known byseveral names including the hollow bead, vermicular porosityand wormhole porosity. Its length varies from a fraction of aninch to several inches. Radiography exposes the presence ofthe problem clearly.
Welding DC(-) (negative polarity) on the stringer bead will not be harmful to either mechanical or metallurgicalproperties.
Hollow bead or wormhole porosity may also be caused bypoor joint preparation and/or cleanliness. See RecommendedProcedures for Properly Cleaning Pipe.
Filler, stripper and cap
In general, there is little fault found with the fillers, strip-pers and caps. Most of this welding today is being done with3/16≤ (4.8mm) Shield-Arc® HYP or 70+ at 160–180amps andthe results have been excellent.
A reasonably competent crew of firing line welders armedwith FW5P+, HYP or 70+ can do a very fine job of finishingthe weld if the stringer and hot pass crew have been doingtheir work properly.
The size and consistency of the final weld will have its influ-ence on the x-ray radiograph. Thus, the firing line weldersshould be encouraged to produce a cap pass which is asuniform as possible with neatly stitched close ripples and asmuch reinforcement as required.
Welding cracks
Since the advent of the higher tensile pipe steels (5LX 52,60, 65, 70 etc.), it has been necessary to exercise better pro-cedural control to eliminate the possibility of weld and heat-affected zone (HAZ) cracks. To do this effectively, all of thefollowing factors must be controlled.
Vermicular porosity occurs most readily when welding highsilicon pipe—generally above .10% silicon. It is aggravated byexcessive travel speeds and high currents. Welding thestringer bead with 5/32≤ (4.0mm) electrode at 130–165ampsDC(+) and 12 to 14 in/min (0.3 to 0.4m/min) travel speedminimizes its occurrence. DC(-) (negative polarity) should beused for stringer bead welding when burn-through, internalundercut and hollow bead defects are a problem. These prob-lems generally occur on thin wall pipe and on pipe steels containing over .1% silicon. Lower currents can be used withDC(-) which helps to reduce these problems. Travel speedwith DC(-) will be equal to travel speeds with DC(+).
Hot pass and all other passes should be run DC(+) (positive polarity).
Figure 14. The correct angle can only be determined by observing the shape and location of the bead. If the bead drifts to oneside for any reason, it will leave a deep undercut on the opposite sidewall. Tilting the electrode just a few degrees toward the under-cut side will straighten the bead up. This change must take place rapidly if the correct bead placement is to be maintained.
66 Pipeline Rules of Thumb Handbook
9. Remove slag from each bead by power wire brushing.Grinding should not be necessary except possibly toclean up a lumpy start, humped up center or perhapsto improve a crater condition. NOTE: Grinding of thestringer bead should be done with a 5/32≤ (4.0mm) disc.Excessive grinding can be detrimental.
10. Weld stringer beads with two or more persons weldingon opposite sides to equalize stress. Use 3 welders on20–30≤ (508–762mm) pipe; 4 welders on larger pipe.
1. Joint preparation and root spacing must be as specifiedin the approved procedure. (See Figure 6.)
2. Hi-Low conditions must be held to a minimum.
3. Weld 5LX70 with Shield-Arc® 70+. Weld 5LX65 andlower with Shield-Arc HYP or Fleetweld 5P+.Fleetweld 5P+ is recommended for all stringer beadswhen lower hardness is a consideration. Lower stringerbead hardness will result in improved resistance to heataffected zone cracking.
4. The need for preheat varies considerably betweenapplications. Cracking tendencies increase with highercarbon and alloy content, thicker pipe wall and diam-eter (faster quench rate), and lower ambient tempera-ture. Preheat cold pipe to at least 70°F (21°C). Preheatto as much as 300°F (149°C) may be required to slowthe quench rate and prevent cracking when weldinghigh strength, large diameter or heavy wall pipe. Spe-cific preheat requirements must be determined foreach situation based on these considerations.
5. Ideally the line-up clamp should not be removed nor should any movement of the pipe take place untilthe stringer bead is 100% completed. Any movementof the pipe could cause a partially completed stringerbead to be overstressed and to crack. The tendency for such cracking varies with the chemistry of the pipe,its diameter and wall thickness and its temperature.Under favorable conditions it may be possible toremove the line-up clamp with as little as 60% of thestringer bead completed, but this should be done onlywhen it has been clearly demonstrated that this prac-tice does not cause cracks to occur.
6. After removal of the line-up clamp, the pipe must begently and carefully lowered on skids.
7. Use only enough current on the stringer to get a goodinside bead and travel slowly to get the maximum weldcross section.
8. Restrict lack of penetration on the inside bead at tie-ins to 1/4≤ (6.4mm) or less. Use a disc grinder toimprove this situation on starts and stops only.
11. Start the hot pass immediately after completion of thestringer—always within five minutes. At least two hotpass welders should be used on each joint, and to putthis pass in as soon as possible after the stringer beadit may require a total of four hot pass welders leap frogging each other to keep up.
12. Minimize the wagon tracks—this area is highly vul-nerable to cracking until the hot pass is completed(Figure 15).
Figure 15. Cracks tend to occur at the area indicated on oneside or the other of the stringer bead. This could eventually prop-agate up through the weld. A properly controlled procedure andgood workmanship can eliminate this condition.
The Lincoln Electric Company strongly recommends forweldments intended for sour gas, sour crude, or othercritical service applications that the customer verifies thatboth the level of hardness and variation in hardness of theweld, heat affected zone, and base plate are withinacceptable limits.
Reprinted with permission—Lincoln Electric Co.
Construction 67
How many welds will the average welder make per hour?
On large diameter pipe where wall thickness has beenincreased, welders average about 100 inches of completedweld per hour.
Example. How many welds per hour will a welder com-plete on 30-inch line pipe if the stringer beads have beenrun?
NC
N
=
= ( )( ) = =
100
10030 3 14
10094 2
1 1. .
. welds per hour or 11 weldsper 10 hour day
N = 4 15. welds per hour or about 42 welds per 10-hour day.Where stringer beads have been run, the average weldercan complete about 140 inches of weld per hour on ordinaryone-fourth-inch wall line pipe. To find the average number ofwelds per hour, divide the circumference of the pipe into 140.
Example. How many welds per hour will a welder com-plete on quarter-inch wall 103/4-inch line pipe, if the stringerbeads have been run?
N
N
= ( )( )
=
14010 75 3 14140
33 76
. .
.
NC
wherecircumference C pipe diameter ininches times
= ( ) =140
3 14.
How much welding rod is required for a mile of schedule 40 pipeline?
For 40-foot joints:
The rule is based on standard weight (schedule 40) pipe,and the usual number of passes, which varies from two forsmall pipe up to four for 16 inches; larger pipe is usuallythinner wall; the rule includes an allowance for wastage.
225
4030
300¥ = pounds per mile for 30-foot joints.
Rule. For 40-foot joints of schedule 40 pipe, multiply thenominal pipe diameter by 221/2; the answer is pounds of elec-trode per mile of pipeline.
Example. 6-inch pipe:
Example. 10-inch pipe, 30-foot joints:
10 221 2 225¥ = pounds per mile
6 221 2 135¥ = pounds per mile.
How many pounds of electrodes are required per weld on line pipe?
Example. How many pounds of electrode will be used perweld on 24-inch line pipe?
Solution. Pounds of electrode = 12 ¥ .25 or 3 pounds per weld.
Pounds of electrode =
102
pounds per weld.¥ =. .25 1 25Divide the nominal pipe size by two and multiply the result
by one-fourth pound.
Example. How many pounds of electrode will be used perweld on 10-inch line pipe?
Pounds of electrode =
N2
¥ .25
68 Pipeline Rules of Thumb Handbook
Welding criteria permit safe and effective pipeline repairBattelle Laboratories studies show weld sleeves and deposited weld metal can be applied without removing defective lines from service
J. F. Kiefner, Senior Research Engineer, Battelle Houston Operations
Deposited weld metal completely fills and eliminatesclearly visible defects such as corrosion. Access to an entiredefect is required so that weld metal can penetrate and bondto sound metal. It may be possible to enlarge pits, laps, orundercut by grinding a groove wide enough to permit access.Deposited weld metal can be selected when requirements toprevent burn-through are met. These requirements are dis-cussed later.
Removal of a damaged pipe section is another way of elim-inating a defect. The line must be taken out of service,purged, removed and replaced with a sound tie-in piece.Removal is often a poor economic choice in terms of wastedproduct and interrupted service. Thus, removal is recom-mended in Table 1 with the understanding that it may not bepractical in certain instances.
Removal by hot-tapping takes advantage of a widelyaccepted method for making branch connections on livepipelines. The coupon removed from the line must containthe entire defect. Limitations of this technique will be dis-cussed later.
Types of defects
Classes of defects listed in Table 1 are:
• Manufacturing defects—cracks, undercut, lack of fusion,and lack of penetration in seam welds; laps, pits, cracks,and rolled-in slugs in the pipe body; hard spots.
• Environmentally caused defects—selective corrosionand hydrogen stress cracking in electric resistancewelded or flash welded seams; general pipe corrosion;pitting corrosion; stress corrosion cracks; hydrogen stresscracking in hard spots.
• Defects caused by outside forces which include dentsand gouges.
• Construction defects.
Submerged arc-welded (SAW) seam defects, both straightseam and spiral, include undercut, incomplete fusion, incom-plete penetration, and cracks. Repair methods recommendedfor these defects are shown in Table 1. No filler is requiredwith sleeves because after the weld reinforcement is groundflush, no gap between the pipe and sleeve should exist.Removal by hot-tapping is not recommended because the tapwould involve cutting through the seam, a practice consideredunacceptable by many companies. Repair by deposited weld
Research conducted by the American Gas Association(AGA)1–5 and others6–8 showed that pipeline defects can berepaired without removing the lines from service. Two repairmethods evaluated were full-encirclement sleeves and directdeposition of weld metal on defects.* To ensure minimumrisk when using these methods, criteria for repairing pipelinesin service have been formulated (Table 1).
The criteria in the table are intended as a repair guide forlines that operate at 40 percent of their specified minimumyield strength (SMYS) or more. The criteria may by unnec-essarily restrictive for lines which operate at or below 40percent of SMYS.
Note that defects in pressurized pipelines, especially pneumatically pressurized lines, can cause sudden cata-strophic ruptures. When the procedures are carefullyplanned, risks are minimized. Nevertheless, repair errorscould reduce the safety margin of these criteria. Conse-quently, users of Table 1 are urged to exercise caution whenperforming repairs.
Choice of repair method
The repair method options included in Table 1 are:
• Type A sleeve• Type B sleeve• Deposited weld metal• Removal• Removal by hot-tapping
Type A sleeve repair consists of placing a reinforcing bandconcentric with the pipe while leaving the band ends un-sealed. The sleeve strengthens a defective area by restrainingbulging that would otherwise occur when the weakened pipeshell is pressurized. Such a sleeve may also carry a smallportion of the hoop stress, but in no case can it become thesole pressure containing element since its ends are not sealed.As a result, it cannot be used to repair a leaking defect. If agap exists over the defect, filling of the gap is required. Twoclasses of Type A sleeve exist: no filler; with filler.
Type B sleeve repair requires a pressure-tight reinforcingconcentric band. Its ends are sealed to the carrier pipe and itcan contain pressure. It can be used to repair leaking defects.In addition, a Type B can also be used as a Type A sleeve.Three classes of Type B sleeves exist: no filler; with filler; pressurized.
Construction 69
spot from the environment, which may cause it to becomecracked.* Hard spots at the I.D. surface should not berepaired with Type A sleeves since they may be susceptibleto cracking in certain types of product service. Such a sleevewould not prevent a leak if the resulting crack grew throughthe wall.
Selective corrosion and hydrogen stress cracking in ERWand FW seams are subject to low toughness fracture behav-ior. It is recommended that they be removed or repaired withpressurized Type B sleeves to relieve stress.
General or widespread corrosion is that which covers toowide an area to be repairable by means of hot-tapping ordeposited weld metal. Any other repair means are acceptableif they cover the critically affected area. When internal cor-rosion is present, its extent must be reasonably well knownand further corrosion must be prevented. Removal maysometimes be the only suitable choice.
Pitting corrosion may involve isolated pits or groups of pits.Generally, isolated single pits will not require repair if furthercorrosion can be halted. ASME guidelines can be used todetermine whether or not a corroded region requires repair.Groups of interacting pits can substantially lower remainingstrength. If strength has been lowered, the pipe should berepaired. Any of the methods of Table 1 are suitable if thenoted precautions are observed.
Stress-corrosion cracks occur in clusters and often coverlarge areas. It is difficult to repair these cracks by hot-tappingor deposited weld metal. Repair methods for stress-corrosioncracks are confined to those which can strengthen the entireaffected area.
Hydrogen stress cracking appears in hard spots attacked byhydrogen emitted from bacteria external to the pipe and fromcathodic protection. Internally the hard spots can be attackedby certain types of products—especially those containinghydrogen sulfide. Because flatness often occurs near hardspots, nonfilled sleeves are not recommended. Depositedweld metal is not recommended because grinding of a hydro-gen stress crack in a hard—and usually brittle—spot while thepipe is under pressure is not safe. Interior hydrogen stresscracking should not be repaired by a Type A sleeve since sucha sleeve cannot prevent leaks if the crack grows through the wall.
Dents and gouges and a combination gouge-in-dent resultfrom external encroachment by mechanical excavating equip-ment, other kinds of equipment, or rocks. Plain dents are
metal is applicable only for undercuts and is subject to specialrequirements given in footnotes of Table 1.
Type B pressurized sleeves used on nonleaking defects canbe pressurized only by using a tapping nipple. Since othermeans of sleeve repair are entirely adequate when used asdirected, the intentional pressurization of a sleeve when noleak or near leak is present is not necessary.
Inside or interior defects require special considerationsince they are not readily visible. Removal may be the bestalternative unless one can be reasonably certain of the extentof the defects. Hot-tapping is not recommended because ofthe uncertainty of the extent of an inside or interior defect.
Electric resistance welded (ERW) or flash welded (FW)seam defects include: upturned fiber imperfections; incom-plete fusion; penetrators; cold welds; cracks. These can onlybe repaired with pressurized sleeves and removal since thewelds are susceptible to brittle fracture or low-resistanceductile fracture initiation. The value of restraint of bulgingfrom either type of nonpressurized sleeve is uncertain. Hencethey are not recommended for these defects. Hot-tappingalso is not recommended because of the involvement of the seam weld. It is not recommended that weld metal bedeposited because of possible low ductility. Required grind-ing before such welding would involve creating or enlarginga defect in a potentially low-toughness material. Only removalor use of a Type B pressurized sleeve which stress-relieves thedefect is recommended.
Other seam defects include lap welds and furnace buttwelds. These must be dealt with on a case by case basis. Suchwelds usually appear in older or smaller and lower pressurepipelines where fracture resistance requirements are lessstringent. On the other hand, some of these older materialscan be quite susceptible to low-toughness fracture behavior.It is probably best to treat these materials with the samecaution as ERW and FW seams as they are being operated atstress levels exceeding 40 percent of SMYS.
Laps, pits, seams, cracks, and rolled-in plugs should berepaired subject to these limitations: special requirements ofI.D. and interior defects and leaks must be observed; hot-tapping is acceptable on nonleaking, O.D. defects as long asthe entire defect is removed with the coupon; deposited weldmetal may be used to repair pits or laps if they can be entirelyexposed by grinding.
Hard spots created in the plate by accidental quenching onthe run-out table may become flat spots in the pipe since theydo not yield when the plate is formed to pipe. Such hard spotsdo not fail spontaneously unless they contain quench cracks,or unless they undergo hydrogen stress cracking. Such spotsshould be repaired if they are not cracked. Type A or B sleeveswithout filler would not be acceptable since they would notrestrain flat spots from bulging.
Hard spots can be remedied by several methods if theyoccur as outside nonleaking defects. Sleeve repair methodswith filler not only provide strengthening but shield the hard
* One method of protecting hard spots from hydrogen stress cracking which,so far, has proven adequate, is that of using a concentric band of sheetmetal spaced away from the pipe by rubber seals. The annular space isfilled with coal tar to exclude ground water, and the metal band (which isitself coated) shields the hard spot from hydrogen generating cathodic pro-tection current.
70 Pipeline Rules of Thumb Handbook
deposited weld metal. Gouges-in-dents may be repaired onlyby means which prevent outward movement of the dent.Sleeves without fillers are not acceptable.
When dents are involved, hot-tapping is not recommendedsince it may not remove the dent entirely. For any gouge orgouge-in-dent, repair by deposited weld metal is not recom-mended since concealed cracks may exist. When a dent ispresent, weld metal may not have sufficient ductility to with-stand the severe strains that accompany outward dent movement.
Construction defects in girth weld include undercut,incomplete fusion, incomplete penetration, and cracks.Deposited weld metal may be one of the best ways to repairundercut or other externally connected defects in girth weldswhich can be ground for access. Sleeves, if used, should have
usually innocuous unless they are quite large*—2 percent ormore of the diameter—or unless they involve a seam or girthweld. When the dent is large or welds are included in the dentor gouge-in-dent, the repair should prevent its outward move-ment. Sleeves with fillers or pressurized sleeves are required.If the included weld is an ERW or FW seam, the defectshould be removed or the stress relieved with a pressurizedsleeve.
Gouges without dents in the body of the pipe or in SAWseams or girth welds may be repaired by any means except
* Present requirements of federal regulations Part 192 dictate removal ofdents extending over 2 percent of the pipe diameter.
Table 1Criteria for selecting an appropriate repair method (X indicates an acceptable repair)
Type of defect
Manufacturing defectEnvironmentally caused defect in ERW or FW
In seam weld In the body of the pipe Seam weld in body, SAW seam or girth weld
ERW and FWUpturned
SAW fiber SelectiveUndercut, imperfection, Hard spot corrosion,
Incomplete Penetrator, Crack and 2 in. cracking Stress- crackingpenetration, Cold weld, Rolled-in in extent in weld General Pitting corrosion in hard
Repair method Crack Crack Slug or more zone corrosion corrosion cracking spot
Nonleaking O.D. defect(a)
Type A sleeve No filler X ...... X ...... ...... X X X ......Type A sleeve With filler ...... ...... ...... X(g) ...... X X ...... XType B sleeve No filler X ...... X ...... ...... X X X ......Type B sleeve With filler ...... ...... ...... X ...... X X ...... XType B sleeve pressurized X(b) X(b) X(b) X(b) X(b) X(b) X(b) X(b) X(b)
Deposited weld metal(h) X(c) ...... X(c) ...... ..... ...... X(c) ...... ......Removal X X X X X X X X XRemoval by hot tap ...... ...... X(e) X(e) ...... ...... X(e) ...... X(e)
Nonleaking interior or I.D. defect(a)
Type A sleeve No filler X ...... X ...... ...... X X ...... ......Type B sleeve No filler X ...... X X ...... X X ...... XType B sleeve pressurized X(b) X(b) X(b) X(b) X(b) X(b) X(b) ...... X(b)
Removal X X X X X X X ...... X
Leaking defects
Type B sleeve pressurized X X X X X X X X XRemoval X X X X X X X X X
(a) Corrosion or other defect which is known to exceed 80 percent of the wall thickness in depth should be treated as though it were a leak.(b) Pressurization to be accomplished upon completion of repair by drilling hole through carrier pipe through a small tapping nipple.(c) Only for undercut, laps, and pits where the defect can be safely enlarged to a weldable groove and subject to remaining wall thickness rules.(e) Only if branch coupon entirely contains and removes defect.(f) Only with humped sleeve or if flat sleeve is used, girth weld must be ground flush. Do not use if extreme high-low condition exists.
Construction 71
input; nature and state of the pressurization media in thepipe. Consequently, it is possible to prescribe safe limits foravoiding burn-through while depositing weld metal on adefect (Table 2).
Table 2 shows a relationship between I.D. surface temper-ature during welding and remaining wall thickness for variouspressure and flow rates of natural gas. These values weretaken from AGA curves. The table is based on: heat inputcharacteristics of the 3/32-inch or 1/8-inch low hydrogen elec-trode; 80 to 100 amps welding current at 20 volts DC; anaverage electrode travel speed of 4 to 5 in./min.
Energy input should not exceed these limits. Low hydro-gen electrodes are recommended for reasons explained later.Under these conditions, repairs can safely be made in the flat,
a special shape such as a central hump to avoid interferencewith the girth weld reinforcement. Only sleeves with weldedends are recommended. Such sleeves tend to strengthen thedefective girth joint, whereas those with nonweld ends do not.
Burn-through
Burn-through into a live pipeline would defeat the pur-pose of a repair, would probably cause the line to be shutdown, and might create a serious safety hazard to the repaircrew.
An AGA study revealed that the following parameterscontrol burn-through: remaining wall-thickness; welding heat
Defect caused by outside force Construction defect
In seam or other weld In body of pipe In girth weld
Plain dent or Gouge (Alsogouge-in-dent, Plain dent, gouge Plain dent Including gouges Undercut, Incomplete,SAW Seam or or gouge-in-dent greater than 2% in SAW seams fusion Incomplete
Girth weld ERW or FW seam of pipe diameter or girth welds) Gouge-in-dent penetration, Crack
...... ...... ...... ...... ...... ......X ...... X ...... X ......
...... ...... ...... X ...... X(f)
X ...... X ...... X ......X(b) X(b) X(b) X(b) X(b) X(b,f)
...... ...... ...... X(b) ...... X(c)
X X X X X X...... ...... ..... X(e) ...... ......
...... ...... ...... ...... ...... ......
...... ...... ...... ...... ...... X(f)
...... ...... ...... ...... ...... X(b,f)
...... ...... ...... ...... ...... X
X X X X X X(f)
X X X X X X
(g) One method of protecting hard spots from hydrogen stress cracking which, so far, has proven adequate is that of using a concentric band of sheet metal spaced away from the pipe by rubberseals. The annular space is filled with coal tar to exclude ground water, and the metal band (which is itself coated) shields the hard spot from hydrogen-generating cathodic protection current.The role of this band is merely to shield the pipe from the cathodic protection and not to strengthen the pipe.
(h) Use of low hydrogen electrodes is recommended.
72 Pipeline Rules of Thumb Handbook
procedures for making these welds, with a minimum risk ofcracking, are available.1,4,5,8
In the case of deposited weld metal repairs, heat input mustbe kept low to avoid burn-through during the first or secondpasses. During later passes, however, higher heat inputs canbe used to soften the resulting repair metal microstructureand the heat-affected-zone of base metal. A high heat inputfinal pass can be made with a nonfusing tungsten electrode assuggested by the British Gas Corp.8 An alternative procedureis to make an extra pass with high heat input using a conven-tional electrode. This pass can be ground off since its purposeis merely to soften the heat-affected microstructure of previ-ous passes.
(Based on a paper, “Criteria for Repairing Pipelines inService Using Sleeves and Deposited Weld Metal” presentedby the author at the AGA Transmission Conference at Mon-treal, Que., May 8–10, 1978.)
Source
Pipe Line Industry, January 1980.
References
1. Kiefner, J. F., and Duffy, A. R., A Study of Two Methodsfor Repairing Defects in Line Pipe, Pipeline ResearchCommittee of the American Gas Association, 1974,Catalog No. L22275.
2. Kiefner, J. F., Duffy, A. R., Bunn, J. S., and Hanna, L. E.,“Feasibility and Methods of Repairing Corroded LinePipe,” Materials Protection and Performance, Vol. III,No. 10, Oct., 1972.
3. Kiefner, J. F., “Corroded Pipe: Strength and RepairMethods,” Fifth Symposium on Line Pipe Research,Houston, Texas, 1974, American Gas Association, CatalogNo. L30174.
4. Kiefner, J. F., “Repair of Line Pipe Defects by Full-Encirclement Sleeves,” Welding Journal, Vol. 56, No. 6,June, 1977.
5. Kiefner, J. F., Whitacre, G. R., and Eiber, R. J., “FurtherStudies of Two Methods for Repairing Defects in Line Pipe,” to Pipeline Research Committee of theAmerican Gas Association, NG-18 Report No. 112,March 2, 1978.
6. Cassie, B. A., “The Welding of Hot-Tap Connections to High Pressure Gas Pipelines,” J. W. Jones MemorialLecture, Pipeline Industries Guild, British Gas Corp.,October, 1974.
7. Morel, R. D., Welded Repairs on API 5LX-52 Pipe, 13thAnnual Petroleum Mechanical Engineering Conference,Denver, Colorado, September 24, 1958.
horizontal or overhead positions provided flow or pressure iscontrolled. Analytic results predict that the I.D. wall temper-ature will not exceed 2,000°F and a burn-through is highlyunlikely when repairs are made in this manner.
Values shown in Table 2 are believed to be quite conser-vative. Repairs were made without burn-throughs on 0.180-inch remaining wall with air at ambient pressure and no flowinside the pipe. This conservatism provides an extra safetymargin and allows linear extrapolations for values betweenthose shown in the table. The minimum wall-thickness of0.150-inch is established on the basis of the experimentalresults. This thickness is also recommended by the British GasCorp. Within these limits, repairs may be made by depositedweld metal (Table 1).
Underbead cracking
Underbead cracking can be minimized by making repairswith low hydrogen electrodes in a manner that avoids hardweld heat-affected zones.
One way to help assure that extremely hard weld zones arenot formed during repair welding is to limit repairs to wellknown carbon equivalent ranges. Unfortunately, chemistriesof specific samples needing repairs will seldom be known.Low hydrogen electrodes prevent hydrogen from beingpresent in the welding atmosphere but they do not preventformation of hard weld zones when adverse chemistries arepresent. Making of crack-free weldments requires carefulcontrol of heat input to avoid rapid quenching or post-repairtreatments to assure that extreme hardness does not remain.
In the case of sleeves, the critical area in which creakingmost often occurs is the fillet-weld at the ends. At least two
Table 2Limitations on remaining wall-thickness for repairing
without a burn-through
Values are the minimum recommended thicknesses in incheswith natural gas as the pressurizing medium at thepressures and flows shown
Maximum welding voltage, 20 voltsMaximum welding current, 100 amps
10. Eiber, R. J., “Field Failure Investigations,” Fifth Sympo-sium on Line Pipe Research, American Gas Association,1974, Catalog No. L30174.
11. Wright, R. R., “Proper Inspection Methods MinimizePipeline Failures,” Oil and Gas Journal, May 23, 1977,pp. 51–56.
8. Christian, J. R., and Cassie, B. A., “Analysis of a LiveWelded Repair on An Artificial Defect,” ERS.C.96,October, 1975.
9. Smith, R. B., and Eiber, R. J., “Field Failure Survey and Investigation,” Fourth Symposium on Line PipeResearch, American Gas Association, 1969, Catalog No.L30075.
TERMINOLOGY9–11
Defect parameters
Defect: A crack, pit, crevice, gouge, dent, metallurgical anomaly, orcombination of two or more of the above which is known or sus-pected to reduce the effective pipe strength level to less than 100percent of its specified minimum yield strength (SMYS).
O.D. defect: A defect emanating at and extending radially inwardfrom the outside surface but not entirely through the wall of thepipe.
I.D. defect: A defect emanating at and extending radially outwardfrom the inside surface but not entirely through the wall of the pipe.
Interior defect: A defect emanating in the interior of the pipe wallbut not of sufficient radial extent to be connected with either theinside or the outside surface.
Leaking O.D. defect: A defect which was initially an O.D. defect,but which has grown through the wall to become a leak.
Leaking I.D. defect: A defect which was initially an I.D. defect, butwhich has grown through the wall to become a leak.
Superficial defect: A lap, crevice, pit, group of pits, metallurgicalanomaly, or plain dent (i.e., without scratches, gouges, or cracks)which is of insufficient extent to reduce the effective strength levelof the pipe below 100 percent of SMYS.
Kinds of defects
* (Definitions marked by asterisk are from API Bulletin 5T1 Nonde-structive Testing Terminology, Third Edition, April, 1972.)
Not every conceivable kind of defect in pipe is covered by this list.The list is limited to those which are likely to be encountered in anin-service pipeline.
Defects originating from pipe manufacture
(a) Defects not necessarily in the seam weld (primarily in the bodyof the pipe)*Lap: Fold of metal which has been rolled or otherwise worked
against the surface of rolled metal, but has not fused intosound metal.
*Pit: A depression resulting from the removal of foreign materialrolled into the surface during manufacture.
*Rolled-in slugs: A foreign metallic body rolled into the metalsurface, usually not fused.
*Seam: Crevice in rolled metal which has been more or less
closed by rolling or other work but has not been fused intosound metal.
*Hard spot: An area in the pipe with a hardness level consider-ably higher than that of surrounding metal; usually caused bylocalized quenching.
*Crack: A stress-induced separation of the metal which, withoutany other influence, is insufficient in extent to cause completerupture of the material.
(b) Defects in the seam weld*Incomplete fusion: Lack of complete coalescence of some
portion of the metal in a weld joint.*Incomplete penetration: A condition where weld metal does not
continue through the full thickness of the joint.*Under-cut: Under-cutting on submerged-arc-welded pipe is the
reduction in thickness of the pipe wall adjacent to the weldwhere it is fused to the surface of the pipe.
*Weld area crack: A crack that occurs in the weld deposit, thefusion line, or the heat-affected-zone. (Crack: A stress-inducedseparation of the metal which, without any other influence, issufficient in extent to cause complete rupture of the material.)
*Upturned fiber imperfection: Metal separation, resulting fromimperfections at the edge of the plate or skelp, parallel to thesurface, which turn toward the I.D. or O.D. pipe surface whenthe edges are upset during welding.
*Penetrator: A localized spot of incomplete fusion.*Cold weld: A metallurgically inexact term generally indicating a
lack of adequate weld bonding strength of the abutting edges,due to insufficient heat and/or pressure. A cold weld may ormay not have separation in the weld line. Other more defini-tive terms should be used whenever possible.
Defects originating from external or internalenvironmental degeneration of the pipe
(a) Seam weld defectsSelective corrosion: Preferential corrosion in the fusion line of an
electric resistance welded or flash welded longitudinal seam.Hydrogen stress cracking: Environmentally stimulated cracking
of the weld metal or heat-affected-zone of the longitudinalseam.
(b) Defects not in the body of the pipe (possibly in the seam weld—but not specifically because of the seam weld)
Guidelines for a successful directional crossing bid package
Development and uses
Originally used in the 1970s, directional crossings are a mar-riage of conventional road boring and directional drilling of oilwells. The method is now the preferred method of construc-tion. Crossings have been installed for pipelines carrying oil,natural gas, petrochemicals, water, sewerage and other prod-ucts. Ducts have been installed to carry electric and fiber opticcables. Besides crossing under rivers and waterways, installa-tions have been made crossing under highways, railroads,airport runways, shore approaches, islands, areas congestedwith buildings, pipeline corridors and future water channels.
The Directional Crossing Contractors Association (DCCA)has been addressing the issue of what information should bemade available to contractors and engineers so that futureprojects proceed as planned. Crossings of rivers and otherobstacles using directional drilling techniques are increasinglybeing utilized around the world. As in any constructionproject, it is necessary for the contractor to have as muchinformation as possible to prepare a competitive and com-prehensive proposal and to be able to successfully install thecrossing. Better preconstruction information also allows thework to be undertaken more safely and with less environ-mental disturbance.
74 Pipeline Rules of Thumb Handbook
Cross country pipeline—vertical down electrode consumption, pounds of electrode per joint*
WallThickness 5/16≤ 3/8≤ 1/2≤ 5/8≤ 3/4≤
Elec. Dia. 5/32≤ 3/16≤ Total 5/32≤ 3/16≤ Total 5/32≤ 3/16≤ Total 5/32≤ 3/16≤ Total 5/32≤ 3/16≤ Total
* “Electrode required.” Figures in the table include 4-in. stub lengths. These figures will vary with different stub loss practices.Quantities required for the 5/32≤ size will vary based on travel speeds of the stringer bead and hot pass. Slow travel speeds may increase thesequantities by up to 50%.
Reprinted courtesy of the Lincoln Electric Company.
