Defect assessment is the engineering process of evaluating a pipeline defect to determine whether it is acceptable for continued operation, requires monitoring, repair, pressure reduction, or immediate replacement.
In the pipeline integrity industry, defect assessment typically includes the following steps:
Identify the defect
- Metal loss (internal or external corrosion)
- Crack-like defects
- Dents
- Gouges
- Laminations
- Weld defects
- Wrinkles or buckles
- Mechanical damage
Collect defect data
- Pipe outside diameter (OD)
- Wall thickness (WT)
- Material grade (e.g., API 5L X52, X65, X70)
- SMYS
- Operating pressure / MAOP
- Defect depth (%WT)
- Defect length
- Defect width (when applicable)
- Corrosion type (general or localized)
Select the assessment method
Common industry standards include:
- ASME B31G
- Modified B31G
- RSTRENG
- DNV-RP-F101
- API 579-1/ASME FFS-1
Calculate remaining strength
Determine:
- Remaining strength factor (RSF)
- Failure pressure
- Safe operating pressure
- Maximum allowable operating pressure (if reassessed)
- Safety factor
Compare with operating conditions
Compare the calculated failure pressure with:
- Current operating pressure
- Design pressure
- MAOP
- Hydrotest pressure (if applicable)
Make an integrity decision
Typical outcomes are:
- Continue operating
- Monitor corrosion growth
- Reduce operating pressure
- Install a repair sleeve
- Composite wrap repair
- Replace pipe section
- Immediate shutdown (if critical)