Nemo Engineering AS (Nemo) has built a series of Tees for welding into offshore pipelines for transportation of hydrocarbons. The purpose with the Tees is to allow connection of new pipelines from existing or future oil and gas fields. This is often a cost-effective solution which minimises the need for construction of new pipelines. Some of the Tees are designed with open tee branch which is isolated with a ball valve system. Another solution is to design a Tee where the branch is blinded off by a solid steel barrier plate. This is a socalled Hot Tap Tee (HTT). At the time when a new pipeline is to be connected to the HTT, the steel barrier plate is drilled open by a core drill operation. This operation is performed when the pipeline is at full flow and operational pressure. The core drill operation is complex and requires a large amount of subsea tooling equipment. In addition, the operation is time consuming and involves elements of risk in case of failing equipment. Nemo Engineering as is currently working on the Ormen Lange project where two HTTs at 850 m water depth will be opened by core drilling in 2009 for connection of pipelines from a new gas field (Ormen Lange Southern Field).
During this project, equipment for blinding/sealing of the opened HTT’s has been developed. This is an Isolation Plug (IP), which is used to seal off the open HTT. The purpose with the IP is to use it in case of future disassembly of the connected pipeline and isolation ball valve without compromising the integrity and operational service condition for the HTT-pipeline. Nemo Engineering as has initiated a development project of a new HTT design where the steel barrier plate is changed out with a combination of using the IP and a steel membrane seal in the tee branch. The membrane will function as asubstitution for the thick steel barrier plate and function as a metallic seal until the IP is removed. The idea is that the steel membrane will break when the IP is removed, and the core drilling operation is no longer necessary.
This Thesis contains the work related to preliminary design, modelling, analysis and testing of a steel membrane prototype. The main conclusion from the work is that there is good correlation between the results from the finite element analysis and the observed test loads.