Wall Thickness Analysis for Offshore Pipelines
The offshore pipelines and risers wall thickness is assessed against the following possible modes of failure based on subsea pipeline design code:
- Hoop stress (pressure containment)
- Collapse due to external pressure
- Buckle initiation
- Buckle propagation
- Buckle initiation
As part of the detailed engineering design, preliminary pipelay and installation analyses should be carried out to further confirm the acceptability of the selected wall thickness and material grade.
Wall Thickness Analysis for Onshore Pipelines
The onshore pipelines is assessed against the Hoop stress (pressure containment) based on ASME 31.8 for the gas transmission pipelines and ASME 31.4 for the liquid hydrocarbons pipelines.
The wall thickness calculation is performed using an in-house program calculation sheet.
Material Grade Selection
The steels applied in the offshore oil and gas industry vary from carbon steels (taken from American Petroleum Institute standards- Grade B to Grade X 70 and higher) to exotic steels(i.e. duplex).
The following factors are to be considered in the selection of material grades:
- Cost;
- Resistance to corrosion effects;
- Weight requirement;
- Weldability
