Page 79 - Pipeline Rules of Thumb Handbook

66 Pipeline Rules of Thumb Handbook

1. Joint preparation and root spacing must be as specified 9. Remove slag from each bead by power wire brushing.
in the approved procedure. (See Figure 6.) Grinding should not be necessary except possibly to
clean up a lumpy start, humped up center or perhaps
2. Hi-Low conditions must be held to a minimum.
to improve a crater condition. NOTE: Grinding of the
5
®
3. Weld 5LX70 with Shield-Arc 70+. Weld 5LX65 and stringer bead should be done with a / 32 ≤ (4.0mm) disc.
lower with Shield-Arc HYP or Fleetweld 5P+. Excessive grinding can be detrimental.
Fleetweld 5P+ is recommended for all stringer beads
10. Weld stringer beads with two or more persons welding
when lower hardness is a consideration. Lower stringer
on opposite sides to equalize stress. Use 3 welders on
bead hardness will result in improved resistance to heat
20–30≤ (508–762mm) pipe; 4 welders on larger pipe.
affected zone cracking.
4. The need for preheat varies considerably between
applications. Cracking tendencies increase with higher
carbon 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). Preheat
to as much as 300°F (149°C) may be required to slow
the quench rate and prevent cracking when welding
high strength, large diameter or heavy wall pipe. Spe-
cific preheat requirements must be determined for
each situation based on these considerations.
5. Ideally the line-up clamp should not be removed
nor should any movement of the pipe take place until
the stringer bead is 100% completed. Any movement
of the pipe could cause a partially completed stringer 11. Start the hot pass immediately after completion of the
bead to be overstressed and to crack. The tendency stringer—always within five minutes. At least two hot
for such cracking varies with the chemistry of the pipe, pass welders should be used on each joint, and to put
its diameter and wall thickness and its temperature. this pass in as soon as possible after the stringer bead
Under favorable conditions it may be possible to it may require a total of four hot pass welders leap
remove the line-up clamp with as little as 60% of the frogging each other to keep up.
stringer bead completed, but this should be done only 12. Minimize the wagon tracks—this area is highly vul-
when it has been clearly demonstrated that this prac- nerable to cracking until the hot pass is completed
tice does not cause cracks to occur.
(Figure 15).
6. After removal of the line-up clamp, the pipe must be
gently and carefully lowered on skids.

7. Use only enough current on the stringer to get a good
inside bead and travel slowly to get the maximum weld
cross section.
Figure 15. Cracks tend to occur at the area indicated on one
8. Restrict lack of penetration on the inside bead at tie- side or the other of the stringer bead. This could eventually prop-
1
ins to / 4 ≤ (6.4mm) or less. Use a disc grinder to agate up through the weld. A properly controlled procedure and
improve this situation on starts and stops only. good workmanship can eliminate this condition.

The Lincoln Electric Company strongly recommends for
weldments intended for sour gas, sour crude, or other
critical service applications that the customer verifies that
both the level of hardness and variation in hardness of the
weld, heat affected zone, and base plate are within
acceptable limits.

Reprinted with permission—Lincoln Electric Co.