A previous IPC conference paper (1) described the technical challenges associated with the installation of a new hot tap connection, supplementary to an existing hot tap connection, on the Bord Gáis Éireann Brighouse Bay high pressure gas export terminal in the UK. Work carried out to verify that the hot tap connection would be fit for purpose included a pipe stress analysis, Finite Element Analysis (FEA) and Engineering Critical Assessment (ECA). These assessments were performed because the split tee shell thickness and consequently also the circumferential fillet weld leg lengths did not achieve the 2 × carrier pipe thickness criterion required by UK specifications for applications where design stress levels exceed 30% specified minimum yield strength.
Subsequently, it was identified that the existing hot tap connection installed in 2001 also did not meet the 2 × carrier pipe thickness criterion. Furthermore the material grade was lower than that for newer hot tap, i.e. P355 compared with P460 and the tee had been chamfered down from 50 mm to 40 mm at the ends, leading to reduced section circumferential fillet welds. This resulted in a leaner design than that for the newer hot tap and an ASME B31.3 area replacement calculation revealed that the area replacement ratio barely achieved the 1.0 requirement of the code suggesting a limited tolerance to system loading. Consequently similar stress analysis, FEA and ECA assessments to those previously undertaken were also subsequently performed for the existing hot tap connection. This paper provides details of the analyses and results obtained to determine the integrity of the existing hot tap split tee assembly which required a bespoke approach and a need to challenge conventional thinking.