A quality alternative to welded pipingWednesday November 14, 2001 Written by Chris Peitchinis
Piping systems need not be installed in the same way as they were 50 years ago. Strict cleanliness requirements can be achieved and labour costs reduced by using non-welded piping. Two basic procedures exist for attaching flanges to high-pressure conductors: flaring the pipe to 37 deg.; and grooving the pipe to accept a retain ring. Both involve a non-welded style of flanged connection, which is free to rotate about the conductor. This eliminates the need to be specific on which axis the pipe-fitter aligns the bolt holes of mating flanges. Welding or threading the flanges onto the pipe is unnecessary. The first method, whereby the pipe end is flared to 37 deg., uses two internal cones (see fig. 1). A union joint consists of two flare flanges, on O-ring face cone with an O-ring seal (CO style), and one flat face cone (CF style). Both internal cones have back-up O-rings. The flanges are slipped onto the pipe before flaring; the internal cones are then positioned in the pipe. Bolting the connection together draws the flared pipe and cone into contact with each other, providing an elastometer seal at the flare and the face. Standard flare flanges are available from 0.5" to 3", in SAE or ISO styles, and can withstand pressures to 400 bar. The second method uses heavy wall pipe on the retain-ring connection and has a machined flat surface on the butt-end of the pipe (see figure 2.) An annular groove on the outside diameter accepts the retain ring. After machining, the flange is slipped onto the pipe and retain ring (a segmented stainless steel ring, bound by a spiral-wound stainless steel spring) is sprung over the pipe's outside diameter, nesting in the mechanical annular groove. An O-ring seal retainer is inserted between the two butt-ends of the pipes. Bolting the flanges together draws the pipe against the retain rings and locks it against the O-ring seal retainer. Pipe-sizes from 1.5" to 10" are available with SAE or ISO retain ring-style flanges, again withstanding pressure to 400 bar. Pressure and flow requirements determine the choice of method, the flare system being the most cost-effective. The high-pressure conductor also plays an important role. Many of today's hydraulic systems require ISO cleanliness levels of 13/10 or higher, which necessitates clean fluid conductors. The conductor used is carbon steel, cold drawn, seamless, normalized (without oxygen), zinc phosphate inside and out and manufactured to European Standards DIN 2391c, in ST 52.4 metal grade. Avoiding welding means there is now steel carbonization and no weld icicles inside the pipe. The elimination of acid pickling and neutralizing the conductor offer both environmental and cost benefits. Both non-welded systems used with the cold-drawn metal require a simple oil flush, using the system operating oil as cleaning fluid. Amy L. Woy, project engineer at Republic Engineered Steels, Inc. justifies the cost. "Material costs for the flared and retain ring non-welded systems are marginally higher than a traditional welded pipe system," she says. "But when the material and labour costs were analyzed and combined to identify the total installed system cost, savings were realized. Total installation cost savings far outweighed material costs." Chris Peitchinis is operations/project development manager at Tube-Mac Industries Ltd., Stoney Creek, Ont.