PIPE WELDING


SUPPLEMENTAL INFORMATION 2

 

PIPE WELDING

 

Welding pipe is like welding any other structural shape and welding can take place in any of the normal positions for welding. When welding pipe flanges and some joints configurations the weld applied may be a fillet weld. When welding pipe to pipe the joint is similar to a vee groove and is often open root. Welding pipe to pipe requires a higher degree of skill and is the topic of this supplement.

The pipe welding positions covered are the 1G flat and rolled position, the 2G horizontal position, the 5G vertical position and the 6G fixed position as shown below.

 

 

 

 

PIPE WELDING EDGE PREPERATION

 

The pipe coupons for welding are cut using the pipe beveling machine. The slag is removed and the edges are ground smooth for welding a 1/8 landing or flat is applied to the pipe. The pictures below show the pipe beveling machine and the edge preparation.

 

 

 

 

 

 

PIPE ASSEMBLY

 

The pipe is assembled for welding by placing one piece on top of the other with a 1/8 electrode without flux on it between the pipe.

 

 

It is extremely important to set up and tack weld the pipe properly, if the pipe is not aligned on the inside it is difficult to obtain the proper penetration through the pipe.

The root gap around the pipe must be consistent. If part of the root gap is too wide the key hole will open up too much while welding and instead of penetration you may have burn through (more than 1/8 reinforcement) on the inside. If part of the root gap is too narrow you may not be able to penetrate through the pipe in those areas.

At least 4 tack welds should be placed around the pipe at 12 o’clock 6 o’clock 3 o’clock and 9 o’clock.   

The tacks must be strong enough to hold alignment while welding the root pass and should penetrate enough to become a part of the root pass. When testing the tack may be removed using a cutting wheel to get a consistent root weld around the joint.   

The picture below shows the tacks in a flat position pipe.

Chill ring

For some applications a chill ring may be used instead of an open root. The chill ring works like a backing bar in groove welding and becomes a part of the welded joint. When the chill ring is used the root opening is determined by the pins on the chill ring. After tacking the chill ring on the inside of the pipe, the pins are removed. If a chill ring is used the root pass may be made using E-7018 since it is not necessary to penetrate through the pipe.

 

 

PIPE WELDING IN THE FLAT 1G POSITION

 

Pipe Welding in the flat position requires that the Welder make some adjustments to the normal angles and length of the welds during welding. In the flat position with the pipe being rolled or rotated the push travel angle works best. Shorter lengths of weld are used so that you do not change your travel angle by stretching out of position. The pipe is then rotated before continuing. Stringer beads are used to weld the root, fill passes and cover pass on six inch schedule 80 pipe.  

 

 

 

 

 

 

Technique for welding the 1 G Rolled Pipe

The root pass is made using the E-6010 Electrode to penetrate through the open root pipe. Make sure the amperage (heat) is set correctly to open and maintain the keyhole where the root is s good fit. Use scrap metal and weld in the flat position with the amperage on approximately 100 and adjust the heat as necessary.

The root pass should be flat to convex in appearance on the groove side of the pipe with no holes and should be flush to 1/8 maximum reinforcement on the inside of the pipe.

 

 

 

 

 

 

 

After completing the root pass and evaluating the penetration, grind the groove side of the weld in preparation for the fill passes.

Set the amperage for the E-7018 1/8 Electrode at approximately 120-150 amps to weld the fill passes and the cover passes. Use the stringer bead technique for welding the fill passes and cover passes.

 

 

PIPE WELDING IN THE 2G HORIZONTAL POSITION

 

When welding in the 2g pipe position the pipe is vertical and the weld is horizontal. The pipe is not moved during welding and the welder must move around the fixed position pipe. The preparation and amperage setting should be the same as for the flat position pipe with E-6010 Electrodes used for the root and E-7018 Electrodes used for the fill and cover passes. It is important to layer the fill passes and cover passes from the bottom pipe up to the top pipe, while keeping the weld beads straight and properly overlapped.

 

 

 

 

 

 

 

 

 

PIPE WELDING IN THE VERTICAL 5G POSITION

 

In the 5G pipe position the pipe is horizontal and the weld axis is vertical so that the welding is essentially a vertical weld. When welding some pipes for low pressure applications or small diameter pipe it may be acceptable to weld vertical downward with an electrodes like the E6010 however; most pipes are welded vertical upward with an E-6010 root pass and E-7018 fill and cap.

When welding in the 5G pipe position the weld beads may be either stringers or weaves depending on the job requirements.

At the Delta School Of Trades we use the E-6010 electrode for the open root pass and E-7018 for the fill and cover passes using the vertical upward weave technique.

 

 

 

 

 

TECHNIQUE FOR VERTICAL 5G PIPE WELDING

 

AS always make sure the correct amperage is set for tacking the pieces and the root pass using E-6010 electrodes. Check the machine setting and use an amperage from 90-110.

Use E-7018 for the fill passes and cover pass set at approximately 120-150 Amps.

Use a slight U shape technique with the E-6010 electrode to open and maintain the keyhole. It may be necessary to ride up very slightly on the inside edge of the groove to chill the keyhole if it opens up too much. If the keyhole is too tight, slow down and force it open with the electrode while welding or stop and increase the amperage (heat).

Use a Z motion weave with the E-7018 Electrode keeping the ripples close together and the weld profile flat for the fill and cover passes.

 

VERTICAL UPWARD WEAVES FOR 5G PIPE

 

Stringer Weaves may also be used to weld the fill passes and cover passes. This is an important technique to learn in preparation for welding in the 6G position

 

 

 

 

PIPE WELDING IN THE 6G FIXED POSITION

 

In the 6G Pipe welding position the pipe is set on a 45 degree inclined angle. The weld in this position covers all position welding because the bottom of the pipe is an overhead weld; the top of the pipe is a flat weld and the front and back sides are a vertical upward weld. The pipe is welded using stringer beads except that a slight weave motion must be used to prevent the sides or vertical upward part from sagging and lumping up in the middle of the weld bead.

 

 

 

 

The Electrode angle should remain the same for all passes. Use a slight push angle from bottom to top.

 

CRITICAL ELEMENTS FOR WELDING THE 6G FIXED PIPE

 

As for all pipe welding take the time to set up the pipe properly with a consistent root gap and 4 evenly spaced tacks.

Make sure you have set the correct amperage for the electrode type and size as mentioned earlier.

After running the root, grind the root pass lightly before starting with the E-7018 Electrode.

Remember to use a slight weave motion with the E-7018 to prevent the weld lumping in the middle and to get proper fusion.

Each filler pass should overlap the prior pass without leaving a depression (called wagon tracks) and should show good fusion.

 

 

 

The 6G pipe position is the one used extensively for testing, since it qualifies the welder for all position welding of pipe, grooves, and fillets.

When testing; it is advisable to remove the tacks instead of weld over them to ensure penetration at the root. A wire wheel brush and grinder may be used to keep each pass clean and prevent slag inclusions.

 

Although there are many Codes and Standards that govern the welding and testing of Pipe, the one most widely used and recommended at the school is the AWS D1.1 Structural Welding Code.

The test for SMAW is usually a 6 inch schedule 80 pipe with an open root, and is welded in the 6G position. This test qualifies the welder for welding fillets grooves and pipe in all positions. Also qualifies the welder for pipe sizes from 4 inches to unlimited and wall thickness from 3/16 inch to unlimited.

An optional SMAW test on 4 inch schedule 40 pipe in the 6G position qualifies the welder for all positions welding and pipe sizes from 3/4 to 4 inch with wall thickness from 1/8 to 3/4.

The pipe size recommended for GTAW Certification is the 4 inch sch 40 pipe.

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PIPE WELDING PROCEDURES

Welds that you cannot make in a single pass should be made in interlocked multiple layers, not less than one layer for each 1/8 inch of pipe thickness. Deposit each layer with a weaving or oscillating motion. To prevent entrapping slag in the weld metal, you should clean each layer thoroughly before depositing the next layer.

 

Figure 7-42.-Butt joints and socket fitting joints.

Butt joints are commonly used between pipes and between pipes and welded fittings. They are also used for butt welding of flanges and welding stubs. In making a butt joint, place two pieces of pipe end to end, align them, and then weld them. (See fig. 7-42.)

When the wall thickness of the pipe is 3/4 inch or less, you can use either the single V or single U type of butt joint; however, when the wall thickness is more than 3/4 inch, only the single U type should be used.

Fillet welds are used for welding slip-on and threaded flanges to pipe. Depending on the flange and type of service, fillet welds may be required on both sides of the flange or in combination with a bevel weld (fig. 7-43). Fillet welds are also used in welding screw or socket couplings to pipe, using a single fillet weld (fig. 7-42). Sometimes flanges require alignment. Fig­ure 7-44 shows one type of flange square and its use in vertical and horizontal alignment.

Another form of fillet weld used in pipe fitting is a seal weld A seal weld is used primarily to obtain tight­ness and prevent leakage. Seal welds should not be considered as adding strength to the joint.

JOINT PREPARATION AND FIT-UP

You must carefully prepare pipe joints for welding if you want good results. Clean the weld edges or surfaces of all loose scale, slag, rust, paint, oil, and other foreign matter. Ensure that the joint surfaces are smooth and uniform. Remove the slag from flame-cut edges; however, it is not necessary to remove the temper color.

When you prepare joints for welding, remember that bevels must be cut accurately. Bevels can be made by machining, grinding, or using a gas cutting torch. In fieldwork, the welding operator usually must make the bevel cuts with a gas torch. When you are beveling, cut away as little metal as possible to allow for complete fusion and penetration. Proper beveling reduces the amount of filler metal required which, in turn, reduces time and expense. In addition, it also means less strain in the weld and a better job of design and welding.

 

Figure 7-45.-Angle iron jig.

Align the piping before welding and maintain it in alignment during the welding operation. The maximum alignment tolerance is 20 percent of the pipe thickness. To ensure proper initial alignment, you should use clamps or jigs as holding devices. Apiece of angle iron makes a good jig for a small-diameter pipe (fig. 7-45), while a section of channel or I-beam is more suitable for larger diameter pipe.

TACK WELDING

When welding material solidly, you may use tack welds to hold it in place temporarily. Tack welding is one of the most important steps in pipe welding or any other type of welding. The number of tack welds re­quired depends upon the diameter of the pipe. For 1/2-inch pipe, you need two tacks; place them directly opposite each other. As a rule, four tacks are adequate for standard size of pipe. The size of a tack weld is determined by the wall thickness of the pipe. Be sure that a tack weld is not more than twice the pipe thickness in length or two thirds of the pipe thickness in depth. Tack welds should be the same quality as the final weld. Ensure that the tack welds have good fusion and are thoroughly cleaned before proceeding with the weld.

SPACERS

In addition to tack welds, spacers sometimes are required to maintain proper joint alignment. Spacers are accurately machined pieces of metal that conform to the dimensions of the joint design used. Spacers are some­times referred to as chill rings or backing rings, and they serve a number of purposes. They provide a means for maintaining the specified root opening, provide a con­venient location for tack welds, and aid in the pipe alignment. In addition, spacers can prevent weld spatter and the formation of slag or icicles inside the pipe.

ELECTRODE SELECTION

Select the electrode that is best suited for the posi­tion and type of welding to be done. For the root pass of a multilayer weld, you need an electrode large enough, yet not exceeding 3/16 inch, that ensures complete fusion and penetration without undercutting and slag inclusions.

Make certain the welding current is within the range recommended by the manufacturers of the welding machines and electrodes.

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