| Abstract: | The effect of welding pressure and surface contaminants on butt fusion in a commercial polyethylene gas pipe was studied by measuring the slow crack growth resistance of the joint. Two weld pressures, 1.61 and 0.31 MPa, were used. The contaminants Vaseline, graphite, and Teflon were coated on the surface. It was found that the high pressure produced a weld with much better slow crack growth resistance than that by low pressure. At high weld pressure, Vaseline and graphite showed a negligible effect on weld quality. Teflon greatly reduced the lifetime, especially at low weld pressure. Test results showed that sufficient pressure was necessary to squeeze out the thin skin layer that occurs at the weld interface, along with any contaminants. The butt fusion joints were always much weaker than the reference pipe. This result was attributed to the difference in both cooling rate and molecular orientation between the pipe and weld. © 1992 John Wiley & Sons, Inc. |
