slight circular motion make the second, third, and fourth passes. This motion of the electrode permits greater control and better distribution of the weld metal. Remove all slag and oxides from the surface of each pass by chipping or wire brushing before applying additional beads to the joint.

WELDING DIFFICULTIES

Many of the welding difficulties in metal-arc welding are the same as in oxygas welding. A few such problems include undercut, cracked welds, poor fusion, and incomplete penetration.

Table 7-3 provides an illustration of the most common welding problems encountered during the arc- welding process and methods to correct them.

Every welder has the responsibility of making each weld the best one possible. You can produce quality welds by adhering to the rules that follow.

1. Use only high-quality welding machines, electrodes, and welding accessories.

2. Know the base material that you are working on.

3. Select the proper welding process that gives the highest quality welds for the base material used.

4. Select the proper welding procedure that meets the service requirement of the finished weldment.

5. Select the correct electrode for the job in question.

6. When preheating is specified or required make sure you meet the temperature requirements. In any case, do not weld on material that is below 32°F without first preheating.

7. Clean the base metal of all slag, paint, grease, oil, moisture, or any other foreign materials.

8. Remove weld slag and thoroughly clean each bead before making the next bead or pass.

9. Do not weld over cracks or porous tack welds. Remove defective tack welds before welding.

10. Be particularly alert to obtain root fusion on the first pass of fillet and groove welds.

11. When groove weld root gaps are excessive, build up one side of the joint before welding the pieces together.

12. When fillet weld root gaps are excessive, be sure you increase the size of the fillet weld to the size of the root gap to maintain the strength requirement. In some cases, it is advantageous to make a groove weld l to avoid extremely large fillet welds.

13. Inspect your work after completion and immediately remove and replace any defective weld.

14. Observe the size requirement for each weld and make sure that you meet or slightly exceed the specified size.

15. Make sure that the finished appearance of the weld is smooth and that overlaps and undercuts have been repaired.

PIPE WELDING

Welding is the simplest and easiest way to join sections of pipe. The need for complicated joint designs and special threading equipment is eliminated. Welded pipe has reduced flow restrictions compared to mechanical connections and the overall installation costs are less. The most popular method for welding pipe is the shielded metal-arc process; however, gas shielded arc methods have made big inroads as a result of new advances in welding technology.

Pipe welding has become recognized as a profession in itself. Even though many of the skills are comparable to other types of welding, pipe welders develop skills that are unique only to pipe welding. Because of the hazardous materials that most pipelines carry, pipe welders are required to pass specific tests before they can be certified

In the following paragraphs, pipe welding positions, pipe welding procedures, definitions, and related information are discussed.

PIPE WELDING POSITIONS

You may recall from chapter 3 of this manual that there are four positions used in pipe welding (fig. 3-30). They are known as the horizontal rolled position (1G), the horizontal fixed position (5G), pipe inclined fixed (6G), and the vertical position (2G). Remember: these terms refer to the position of the pipe and not to the weld

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.