32" × 12" In-Line Barred Tee Verification

The Challenge

An in-line barred tee is one of the more demanding components in a subsea pipeline: a large-bore branch connection with internal pig guide bars, which must survive factory acceptance testing, the bending and roller loads of S-lay installation over a stinger, the system pressure test, and then thirty years of operation at 172 barg in 145 m of water.

The internal pig guide bars added a second problem. They are structural members in the flow path, in F65 carbon steel, and they must remain intact for the design life — because a failed guide bar in a late-life gas pipeline is both a pigging obstruction and a potential integrity threat.

Our Approach

Assessed through the full load history in sequence — FAT, stinger, pressure test, thirty years of operation — because the governing case is rarely the operating case.

VORYX team members carried out non-linear finite element verification in ANSYS to ASME VIII Division 2 Appendix 4, assessing the tee through the complete load history in sequence rather than checking each condition in isolation — factory acceptance test, installation on the stinger, system pressure test and operation.

The stinger case required the tee to be assessed under combined internal pressure, bending and roller contact loads representative of the actual S-lay configuration, since the governing stress state during installation is not the same as the operational one.

The internal pig guide bars were qualified as structural members in their own right, with stress linearisation and the relevant limit checks applied against the code categories rather than treated as secondary attachments.

Standards Applied

• ASME VIII Div 2 App 4
• DNV-ST-F101
• ASME B31.8
• BS 7910

Operator and project names are anonymised for confidentiality and disclosed on request. Experience described is that of VORYX team members.