Chapter 14

1. Chapter 14 Gas Metal Arc and Flux Cored Arc Welding of Pipe

2. OBJECTIVES • demonstrate the ability to make root pass welds using GMAW, FCAW-G, and FCAW-S processes. • demonstrate the ability to make hot pass welds using GMAW, FCAW-G, and FCAW-S processes. • demonstrate the ability to make filler pass welds using GMAW, FCAW-G, and FCAW-S processes. • demonstrate the ability to make cover pass welds using GMAW, FCAW-G, and FCAW-S processes. • demonstrate how to grind a tack weld and weld starts and stops to a featheredge. • explain the acceptable criteria of a visual inspection of a pipe weld.

3. KEY TERMS • joint preparation • end preparation • joint cleaning • joint fitup • tack welds • root pass • hot pass • filler pass • cover pass(es) • visual inspection

4. INTRODUCTION • Both GMA and FCA pipe welding processes are combined in this chapter, because in the field they are often used together to make pipe welds. • Before beginning the pipe welds in this chapter, you should have completed many of the GMA and FCA welding practices in Chapters 11 and 13.

5. Joint Preparation • The shaping, cleaning, fitting, and tack welding of pipe joints are critical steps required to make a code quality weld. • Do not try to rush through these steps, take your time and do them correctly.

6. End Preparation • The ends of pipe are beveled to between 30° and 35° to form a 60° to 70° V-groove when they are put together, Figure 14-1.

7. End Preparation (cont.) • Preassembly Joint Cleaning • Once the root face has been prepared, the inside and outside pipe surfaces must be ground clean back 1-in. (25 mm) from the joint. This cleaning is required to prevent surface contamination from causing weld defects. • When grinding, be very careful not to gouge the surface of the pipe, groove face, or root face. • Deep gouges in these surfaces can be considered defects.

9. Joint Fitup • Pipe is not always round; in fact large diameter pipe is almost always out of round. • There are welding gages, called high-low gages, that are specifically designed to check for the alignment of pipe, Figure 14-2. • NOTE: Use a pair of pliers to catch the pipe coupons as they are being cut off so they do not drop to the floor. • Falling to the floor can cause the hot pipe coupon to bend out of round making it harder to fit up properly.

10. Joint Fitup (cont.) • There are several ways to adjust the pipe so it can be aligned properly, if tools specially designed to force pipe section into alignment are not available. • One way is to place the coupon on an anvil and strike it with a hammer. • Another way is to tack the joint together where it is in alignment, and use a clamp or dog and wedge to force the pipe into alignment. • A third way is to use a hydraulic jack inside the pipe to force the joint into alignment.

12. Tack Welds • It is important that tack welds be made with the same welding procedure as the finish welds so that they do not become weld defects in the finished weld. • The number and size of tack welds will vary depending on the pipe’s diameter and wall thickness. • The welding procedure for the pipe you are welding should have the number, size, and location of the required tack welds listed.

13. Tack Welds (cont.) • The ends of the tack welds must be ground to a featheredge so that the root weld can achieve 100% penetration at their ends. • Grinding must be done with a thin grinding disk to ensure that metal on the sides of the groove is not removed as the tack welds are being feathered, Figure 14-4.

15. Root Pass • The root pass can be made uphill or downhill. • It is easier to control the root penetration by making an uphill weld if the root opening is wider than normal. • The uphill technique should also be used if the root opening is narrower than normal. • It is faster, however, to make the root weld using the downhill technique if the root opening is uniform and not too wide or narrow. Both uphill and downhill welds should be practiced.

16. Hot Pass • The hot pass is used to reshape the face of the root weld, burn out any small pieces of trapped slag, and in some cases push the root penetration a little deeper if the root pass did not have 100% penetration all the way around the pipe. • The hot pass can be made with either the GMA or FCA welding process. • Both processes should be practiced so that you will be able to take the SENSE qualification test and so you will have the skills needed for many welding jobs. • The hot pass can be made uphill or downhill; however, it is more difficult to keep good fusion when using the downhill technique.

17. Filler Pass • The bulk of the weld metal added to a groove weld is made up of the filler passes. • These weld passes are typically made in the uphill progression. • They only need to have complete fusion to the previous weld and do not need to have deep penetration.

18. Cover Pass(es) • The cover pass or passes are sometimes called the cap. • These are the final welds that complete the pipe weld. • The visual appearance of the cover pass is often the only inspection that noncritical welds receive.

19. Visual Inspection • Visually inspect the weld for uniformity and discontinuities. • There shall be no cracks, no incomplete fusion, and no overlap.

20. Practice Pipe Welds • Each of the practice welds should be made with GMAW, FCAW-S, and FCAW-G welding processes. • The welds are to be made using the following filler metals and shielding gasses: • GMA welds will be made using 0.035 diameter ER70-S filler metal with 75%Ar + 25%CO2 or Ar + 2% to 5%O2 shielding gas. • Self-Shielded FCA welds will be made with 0.035 or 0.045 diameter E71T-11. • Gas-Shielded FCA welds will be made with 0.035 or 0.045 diameter with 75%Ar + 25%CO2 shielding gas.

21. Pipe to Plate Welds • Pipe sockets are joined to pipe with fillet welds. • Pipe sockets are used in power plants, chemical plants, industrial hydraulics, and architectural applications such as handrails.

22. PRACTICE 14-1 • Fillet Weld, 1F Position, Using GMAW, FCAW-S, and FCAW-G • Using a properly set up and adjusted CP welding machine, proper safety protection, welding electrodes, and one piece of schedule 40 mild steel pipe 3 in to 6 in. (76 to 150 mm) in diameter, and a 4 in or 7 in (100 or 170 mm) ¼ in (6mm) mild steel plate, you will make a pipe-to-plate fillet welded joint in the 1F flat rolled position using each of the three wire welding processes, Figure 14-7.

23. PRACTICE 14-1 (cont.) • The gun should be a slight forehand angle; transition to a perpendicular angle around the 12:00 o’clock position, then on to a slight backhand position as it moves toward the 10:30 o’clock position. • The weld bead should be approximately 3/16 in. (4.8 mm), Figure 14-9.

24. PRACTICE 14-2 • Fillet Weld, 2F Position, Using GMAW, FCAW-S, and FCAW-G • Using the same equipment and materials as practice 14-1, you are going to make a fillet weld in the 2F position using each of the three wire welding processes, Figure 14-10.

25. PRACTICE 14-2 (cont.) • Using a 15° to 20° backhand gun angle and a 35° to 40° work angle, start the weld on one of the tack welds, and make a stringer weld all the way to the center of the next tack weld, Figure 14-11.

26. PRACTICE 14-2 (cont.) • As you get to the tack weld, speed up your travel rate to taper the size of the weld down to make it easier to restart the next weld bead. • Chip and wire brush the weld, and visually inspect it for uniformity and any undercut or overlap. The weld bead should have equal legs of approximately 3/16 in. (4.8 mm). The weld should be equal on both the plate and side of the pipe.

28. PRACTICE 14-2 (cont.) • The second weld pass will be made using the spray metal transfer method. • This weld bead will be placed around the lower side of the first weld so that approximately 2/3 to ¾ of the root weld face is covered by this weld pass, Figure 14-12.

29. PRACTICE 14-2 (cont.) • The third weld pass will complete the cover pass, and it will also be made using the spray metal transfer method. • This weld should be made approximately ½ to 2/3 of the way up on the second weld’s face, Figure 14-13.

30. PRACTICE 14-3 • Fillet Weld, 5F Position, Using GMAW, FCAW-S, and FCAW-G • Using the same equipment and materials as practice 14-1, you are going to make a fillet weld in the 5F fixed position using each of the three wire welding processes, Figure 14-14.

31. PRACTICE 14-3 (cont.) • The gun angle relative to the pipe surface will be constantly changing as the weld progresses upward. • Figure 14-15 shows how the gunangle starts at a slight forehand angle at 6:00 o’clock and becomes perpendicular to the pipe surface around 7:00 o’clock. • It transitions to a steep forehand angle of around 30° between 7:00 o’clock and 9:00 o’clock. • Between 9:00 o’clock and 11:00 o’clock, the angle transitions back to perpendicular and remains perpendicular through the 12:00 o’clock position where the weld ends.

32. PRACTICE 14-4 • Butt Joint, 1G Position, Using GMAW, FCAW-S, and FCAW-G • Using a properly set up and adjusted CP welding machine, proper safety protection, welding electrodes, and two or more pieces of schedule 40 mild steel pipe 6 in to 8 in. (150 to 200 mm) in diameter, you will make a pipe butt joint in the 1G horizontal rolled position using each of the three wire welding processes, Figure 14-16.

33. PRACTICE 14-4 (cont.) • Tack weld two pieces of pipe together with four 1-in (25 mm) long welds at the 12:00, 3:00, 6:00, and 9:00 o’clock positions as shown in Figure 14-17. • Grind the ends of the tack welds before placing the pipe horizontally on the welding table or pipe stand with the top tack welds between the 10:30 and 1:30 o’clock positions.

35. PRACTICE 14-4 (cont.) • Filler Pass(es) • The first filler pass is made along one side so that its toe is about two-thirds of the way across the hot pass. If the toe of the filler pass is made so it meets the opposite sidewall, the V it forms will be likely to trap slag, and it is hard to get the next filler pass to penetrate the narrow gap it forms, Figure 14-18.

36. PRACTICE 14-5 • Butt Joint, 2G Position, Using GMAW, FCAW-S, and FCAW-G • Using the same equipment and materials as practice 14-4, you are going to make a V-grooved weld in the 2G vertical fixed position using each of the three wire welding processes. Prepare the pipe and tack it together as before, then place it vertically on the table or on a pipe stand.

37. PRACTICE 14-6 (cont.) • The beginning and ending points of all of the weld should be staggered so they are not all in the same area and overlap, Figure 14-20. • Slightly increasing the voltage or decreasing the wire feed speed can help to make the weld pool a little more fluid and help increase the hot pass penetration.

38. PRACTICE 14-6 (cont.) • The first filler pass can be made by rocking the welding gun so that the arc is directed from side to side or by using a slight side-to-side weave, Figure 14-21. • This can make a concave weld that can make it easier to prevent slag entrapment and/or undercut along the toe of the weld. • If this technique is used, it is important not to make the weave too large because that can cause excessive buildup and overlap.

39. PRACTICE 14-7 (cont.) • The first filler welds will be made on the downhill side of the groove and cover about two-thirds of the hot pass weld surface. • Each of the next filler welds will be made on the upper side of the previous filler welds, Figure 14-22. • Remember to stagger the starts and stops as you make the filler welds.

40. Summary • The wire welding processes of GMA and FCA welding have become the standard process for many types of piping system construction. • FCAW-G has its limitations for working outdoors when there is anything but a very light breeze because the gas shielding can be easily disturbed.