The Zap-Lok® joint is a mechanical interference connection that, under certain conditions, utilises applied loads to energise a metal-to-metal seal face. One end of the pipe is cold-formed to form a ‘bell’ and the other is formed into a spigot or ‘pin’ as shown in figure 1. These are then subsequently joined in the field by means of a hydraulic press.
The technology has been applied in numerous permanent oil and gas applications both onshore and offshore as an alternative to conventional welding where its inherent speed of construction and mechanical integrity provide a useful means of performing well hook ups.
The purpose of this paper is to draw from the wealth of testing that has been conducted on the Zap-Lok® joint over recent years and present a fully verifiable analytical modelling technique that describes the stress-strain behaviour under typical static operational loading conditions as an orthotropic material. This shall be put forth in the form of a series of stress strain curves as well as a maximum strength model.
In addition, certain requirements shall be put into place in order that pipeline engineers and designers may put into context the various load parameters that exist can be interpreted under the ASME B31 suite of pipeline design codes in order that design and installation shall comply with the aforementioned codes.