Dented Tube Return Bend FEM FFS

SERVICE LINE

• Mechanical Engineering

INDUSTRY SECTOR

• Petrochemical/Chemical Processing

LOCATION
Taranaki, New Zealand

PROJECT SUMMARY
The return bend at the end of a single U-tube exchanger was dented during a reinstallation, resulting in permanent damage to the end of the tube. This could render the tube susceptible to failure from buckling under external pressure.

SCOPE
Based on detail of the flat spot formed at the end of the tube, a fitness for service assessment to API 579-1 Part 12 at level 3 was conducted due to the severity and extent of the dent.

This involved:

• Creating a representative geometry of the return bend.

• Simulating the denting process to create and equivalently sized dent.

• Conducting Finite Element Method elastic-plastic analysis and assessment to API 579-1 Part 12 Level 3 using ASME VIII Div. 2 Part 5 rules.

• Assessing protection against plastic collapse, buckling, ratcheting, and local failure with internal and external design conditions.

CHALLENGES​
Simulation of the denting process was achieved in Finite Element software in order to recreate the extent of the extant dent.

• This is a key criterion for ensuring the model accurately represented reality.

OUTCOME​
The tube return bend was found to have sufficient strength against the failure modes assessed, allowing it to remain in service until the next opportunity arose to replace it given the relative uncertainty around the exact defect geometry.