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 this position
2. Weld a single tack weld in place
3. Measure the location of the pipe or pipe fitting
4. If necessary, adjust the position of the pipe or pipe fitting until it is in the specified location
5. Weld a second tack weld opposite the first tack
6. Check the location of the pipe or the fitting again and, if necessary, adjust the position
7. Weld the two remaining tack welds in place.
Usually all or a number of joints are fitted-up as described above, before the complete root bead is welded, in order to keep the joints flexible so that adjustments can be made in the positions of the pipes. Each joint is held together by the four tack welds, unless it is necessary to weld the entire root bead to enable the joint to carry the weight to which it is subjected. Braces may also be used to support the load.
While the general procedure for fitting-up is the same, regardless of where the job is done, variations in which the details are performed are to be expected. For example, very heavy pipes and fittings have to be lifted by cranes or by chain hoists, using chains or steel cables to hold the pipes or the fittings. On the other hand, smaller pipes can usually be held more conveniently by a helper while the welder welds the first tack weld.
The pipe welder should know the basic methods of fitting-up and should be skilled in their application. He should plan each job in advance. By doing this he can avoid costly errors. Fitting-up is interesting work because it requires thought, planning, and often a considerable degree of ingenuity, since it is seldom that two jobs are the same.