Perfect Weld Requirements

A. The pipe nipples and the edges to be welded should be free from oil, grease, etc.; after they are tacked together, the root openings are inspected. During the course of welding, each layer of welded metal is checked for porosity, undercut, slag inclusion, and surface roughness. An inspector has the responsibility of terminating any […]

Qualification of the Welding Procedure and the Welder

On many welding jobs, the fabricator is required to separately qualify the welding procedure to be used and the welder who is actually to weld the pipe. How this is done is specified by a code. One code frequently encountered in pipe welding is the ASME Boiler and Pressure Vessel Code, Section IX. While this […]

Welding Pipe Parts to Pipe

Flanges. Frequently, a flange must be welded to the end of a pipe, as shown in Fig. 14-6. It must be centered with respect to the axis of the pipe and the face of the flange must be perpendicular to the axis. The bolt holes in the flange are usually in multiples of four and […]

Pipe-to-Pipe Fit-Up

When there are two lengths of pipe that must be fitted-up to — gether, they can be aligned by the methods shown in Fig. 14-4A and B. A very effective method is illustrated in Fig. 14-4A, where an ordinary piece of straight angle (or steel angle) is used as a gage to check the alignment. […]

Tools Required

For very heavy pipes and fittings, tackle is required for lifting and holding them. Chains, steel cable, heavy-duty C-clamps, chain hoists, and cranes are used, if available. Hammers of various sizes, crowbars, and pinch bars are needed occasionally to bend the pipe joints in order to align them. These tools should always be used carefully […]

Fitting-Up Pipe

Fitting-up pipe is one of the basic skills of pipe welding. In simplt terms, fitting-up means to position the pipes in the correct location as specified by the blueprint. The general procedure used to fit-up pipes is basically as follows: 1. Align the pipe or pipe fitting as closely as possible and hold it in […]

Remova of Defects

A defect should be clearly marked by the inspector or supervisor so that the metal can be excised with a minimum of material loss. Normally surface defects and those of reasonable depth can be removed by grinding or gouging. Defects that go into the weld are removed by the gouging method; the weld must be […]


This section discusses some of the proper methods for evaluating and repairing defective welds. The defects covered here are those created during and after welding, such as those caused by improper manipula­tion, insufficient protection of the weld metal pool, oxidation and impurities, and willful neglect to procedures such as proper cleaning, edge preparation and spacing […]

Welding Faults and Their Prevention

Undercutting. When the base metal along the edge of the weld is reduced from its original thickness, as shown in Fig. 13-3, the weld is said to be undercut. There are several reasons why undercutting occurs. Excessive current can cause the edge of the joint to melt and the molten metal will wash into the […]

Restraint Cracking

Restraint cracking is usually associated with small welds made on thick metal sections. This form of cracking occurs in the weld bead and it is caused in part by the solidification and cooling pattern of the weld. Because the parent, or base, metal is much cooler than the weld metal, solidification progresses from the fusion […]