Zap-Lok^® Connection Testing and Axial Strength Design

Zap-Lok^® is a pipe joining technology which relies on radial-interference elastic strain and surface friction to join pipes. The connection consists of a “bell” (expanded end) into which a “pin” (the straight end of the adjoining pipe) is forcefully inserted to provide an interference fit (See Figure 1). Joining is accomplished via a specialized hydraulic joining press provided by Zap-Lok^® which grips both pipe sections and forces them together. A thin layer of the patented epoxy is applied internally to the bell end, and externally to the pin end, to provide lubrication for the insertion. The joining operation takes approximately ten seconds. Both the bell and the pin are formed to specified tolerances per specification by Zap-Lok^® technicians, and may be done in the field or shop. Typical applications include gathering and distribution systems, transmission lines and specialized pipe installations on land and offshore. Of particular interest is the ability to withstand corrosive products with the application of an internal coating that does not sustain damage during the joining operation. To qualify this technology for use extensive testing and analyses was performed. We found that: • In sour service applications the plastic deformation of the bell necessitated a heat treatment to insure that the connection remained NACE compliant. • The axial strength capacity was found to be somewhat less than that of a welded joint. • Burst capacity of the joint was robust. • The joint did not leak even after several cycles of significant plasticity. • Fatigue performance of the joint rivaled that of a lower-end girth weld (i.e. F2 S-N curve). A design method was developed to correctly account for the axial strength using basic ASME-type design concepts. In this presentation we summarize the connection mechanics, testing results, analytical models and design method for the Zap-Lok^® connection.