Weldless Permanent Mechanically Attached Fittings for Subsea Hydraulic Piping
Authors: Amling Theodore T. , Palanci Anthony , Kovacs William 
Published: June 2014

This paper documents the new technology qualification (TQ) process of an Axially-Swaged "Permanent Mechanically Attached Fitting" (PMAF) for subsea hydraulic use. This is a replacment technology for welded pipe fittings used in pressure piping systems for Oil and Gas applications which utilize interconnecting piping between components such as pumps, valves, accumulators, motors, reservoirs, cylinders, filters, etc. Pipe welding is time consuming, expensive, and poses a possible health hazards due to chromium exposure found in stainless steel pipe and fittings. Compared to welded fittings, by using PMAFs installation time can be reduced, production throughput can be improved, and weld related cost and potential chromium exposure can be reduced. PMAFs eliminate many of the time consuming and quality concerns associated with welded pipe systems.

The qualification of the PMAF was carried out in accordance to DNV RP-A203 and the Technology Qualification Plan (TQP). Technology Qualification is defined in DNV RP-A203 as: the process of providing the evidence that a technology will function within specified operational limits with an acceptable level of confidence. A Threat Assessment was conducted to identify all relevant failure modes of concern for the elements defined as new technology and judge the associated risks. This work was carried out in a threat assessment workshop and a Failure Mode Effect and Criticality Analysis (FMECA) was chosen as the most appropriate tool for the Threat Assessment.

A Technology Qualification Plan (TQP) was developed for the purpose of documenting what qualification items would be undertaken in order to qualify the PMAF for the intended service and application, and what would be the acceptance criteria for each test, analysis, document, or procedure. This plan emphasized the failure modes with high or medium risk rankings identified in during the Threat Assessment. The qualification activities were executed at several locations, all were 3rd party witnessed. After which, the risk ranking for each of the failure modes and mechanisms identified in the threat assessment (FMECA) was assessed and updated. High risks were reduced from five (5) to one (1) and medium risks were reduced from 13 to 11.

Many tests, analysis, documentation, and procedure action items were executed during the qualification of the PMAF, including, but not limited to: Vibration testing, SCC corrosion testing, crevice & pitting corrosion testing, HISC corrosion testing, Bending testing, Tension testing, Torsion testing, Burst testing, Impulse testing, and Hyperbaric chamber testing. In addition, extensive Finite Element modeling was performed to support the qualification activities.

This new technology has been designed and tested specifically to meet demanding and unique requirements of sub-sea hydraulic systems. As a new technology it was critical that evidence be provided of functionality and qualification under the application requirement to provide end user confidence. By working closely with customers in the Oil and Gas industry and partnering with independent experts, the PMAF has been proven to meet the challenging demands of the market as a replacement technology for welded fittings used on hydraulic pipe spools.