Abstract
Zohr subsea production system (Accelerated Start Up Phase) is made by 6 wells connected via individual rigid production infield flowlines to two chained Main Subsea Structures. Gas is exported to onshore El Gamil plant through a piggable export sealine connected to the one of the two Main Subsea Structures.
In total 218 km of pipes 30inch to Zohr onshore plant El Gamil pipeline. Pipeline material and dimension combination required for the Zohr project is unique in its kind and the combination of requirements has not been produced before, with demanding mechanical and corrosion tests and a new limit for pipeline exposed to sour service.
A certain number of Buckle arrestors (107 pieces) have been used along pipeline installation. The BAA are around 12 m long and are integrated by three sections; The central sections of thickness (75.8, 66.0 and 54.0mm) are seamless forged pieces produced with ASTM A707 Grade L5 Modified steel in quenched and tempered condition with mechanical properties equivalent to API 5L L415QS / L415QO material. The pup pieces are API 5L LSAW pipes Grade L415MS / L415MO.
During Manufacturing Process Qualification Testing (MPQT) Sulphide Stress Cracking Corrosion Test (SSC) have shown some cracks of test specimens. The specimen fails and SSC cracks were found in the post test analysis, i.e., by sectioning and performing metallography at X100. These specimens were tested in NACE TM0177 type A solution with 5% NaCl and 0.5% acetic acid, saturated with 1 bar H2S at an initial pH of 2.7. Exposure duration was 720 hours and the load to be applied was 90%. No indications or defects were assessed by NDT magnetic particle inspections on all the tested specimens.
Weld overlay of buckle arrestors assemblies (BAA) with alloy N06625 (nominal thickness 3 mm) cover the full length of the central section plus the circumferential welds (that are ground flush) and extending 100 mm on each side of the girth welds into the pup pieces.
It was a challenge to overcome these defect of these pipes considering the stringent requirements in the project specifications and the tight project schedule to achieve the installation campaign without any delay on project schedule.
The Optimized Ramp-Up phase envisages an extension of the Accelerated Start Up subsea system with four (4) additional wells, a new Main Subsea Structure (MSS3), a new Subsea Distribution Unit (SDU) and a piggable export pipeline (30" OD), parallel to the 26" Accelerated Start Up Phase (ASU) export line.
