While working for a contractor overseas about 25 years ago, I often was required to manage construction projects at remote locations. Considering the time it generally took prefabricated and preassembled systems to arrive on-site, this often necessitated on-site fabrication of tees for piping systems with welded joints.
Straight lengths of pipes of different diameters usually were never in short supply at a project site. However, fittings with specific-size tees for different combinations of pipe diameters usually were. In those instances, engineering basics came to the rescue.
The only information needed to field-fabricate a tee connection was the outer diameter of the pipes to be connected — for example, 6 in. by 3 in. I then used a drafting technique called “development of surfaces,” which involved developing a near-exact curve/profile, such as what one would expect to see on the surface of a 6-in. pipe connected to a 3-in. pipe. I also developed another curve/profile that represented the curvature on the end of the 3-in. pipe when connected to the surface of the 6-in. pipe. These two developed surfaces then constituted the “set” for preparation of a 6-in.-by-3-in. tee (figures 1, 2, and 3).
Once the profiles were developed, I wrapped the 6-in.-diameter developed surface on the 6-in. pipe and marked the profile on the pipe (Figure 2). I did the same with the 3-in.-diameter developed surface (Figure 3). The pipes then were cut as per the marked contour. The cut edges were ground for a proper finish/fit, which is similar to how surfaces are prepared for welding.
Once I prepared the contour sheet sets for the various pipe combinations, field-fabricating the tees was effective and no different than putting together a routine welded pipe joint. This technique proved to be particularly cost-effective for large-diameter (greater than 2 in.) pipes.
Asif Kadiani, PE, CEM, LEED AP
Hanson Professional Services Inc.
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