Wall Thickness Design

Riser and Pipeline wall thickness shall compromise the following checks:

• Pressure Containment (bursting)
• System Collapse
• Local Buckling
• Buckle Initiation
• Buckle Propagation

Pressure Containment
Riser and pipeline Hoop stress must be lesser than line pipe specified minimum yield stress, SMYS to prevent pipeline from bursting.

System Collapse
This check is to ensure the pipe has sufficient thickness against failure due to external pressure. This is essential especially for deep water pipeline. (very high external pressure)

Local Buckling
Local Buckling implies gross deformation of pipe section. Local Buckling is due to combined loading (external pressure, bending and axial force) with the most critical combination of hoop stress and longitudinal stress during pipeline installation cases.

Buckle Propagation
Pipeline collapses in an overall shell buckling mode if External Pressure exceeds Buckle Propagation Pressure; otherwise, the pipeline experiences local buckling. The propagation pressure decreases with both the thickness and angular extent of the reduced section, but the rate of decrease with thickness reduction is almost independent of the angular extent of corrosion when it is greater than 90°.

Buckle Initiation
It requires a higher External Pressure to start/initiate a buckle. Although External Pressure is greater than Buckle Propagation Pressure, shell buckle/damage will not occur as long as:
External Pressure ≤ Buckle Initiation