From the GMA Techline
Subject: HDPE welds— For HDPE geomembranes, I am looking for information on what effect there might be, if any, on the integrity of a fusion weld when an extrusion weld is placed directly on top of it. This condition exists when completing patches at T-intersections, but there may be an occasion when an additional section of liner has to be welded directly on top of a fusion weld for greater distance.
Does the reheating of the fusion seam area caused by the extrusion weld cause any deterioration in the fusion weld? If so, to what extent? (Brad, Canada)
Reply: The concern is that the additional heating by the extrusion welding would decrease the molecular weight and have a degrading effect on the material at this sensitive location.
I have data (by Fred Struve) showing that the molecular weight curves of a single melting and a double melting lie right on top of one another.
Send your fax number to me and I will send the curves. That said, there appears to be no problem in this regard.