Case Study 3
WI Pipework

Water Injection pipework suffering for heavy and aggressive internal corrosion
Operating at 3100 psi
Line sizes varied from 4”, 6”, 8”, 10” & 12” so not possible to assess “worst case Scenario”
Some Test Points (TP’s) were being subject to monthly or 3 monthly inspection routines
Requested to conduct FFS on a number of test points (in excess of 20 TP’s showed signs of internal corrosion/erosion damage to varying degrees
Philosophy was to carry out assessments in ascending order starting with code calculations and progressing to Level 1, 2 and 3 as required only on those that failed the earlier assessment levels.

Inspection requirements increased as the Assessment Level increased in order to get the benefit from the less conservative assessment methods.
Code Calculation to PSV set pressure – single minimum thickness value
Level 1 General Metal Loss – multiple point thickness readings
Level 1 Local Metal Loss – single minimum thickness value and defect size
Level 2 Local Metal Loss – corrosion map with thickness profile
Level 3 Linear Elastic FEA Assessment – corrosion map with thickness profile
Level 3 Elastic / Plastic FEA Assessment – corrosion map with thickness profile

Of the 20 TP’s reported 5 were removed from service
Of the 15 TP’s 3 passed a code check or General Metal Loss Level 1 Assessment
Of the 12 remaining TP’s 7 passed a Level 1 or Level 2 Local Metal Loss Assessment.
Of the 5 TP’s that failed the Level 2 only one passed the Level 3 using a Linear Elastic FEA assessment, but did have an increase in MAWPr and hence an increased remnant life.
Of the 4 TP’s subject to an Elastic/Plastic FEA three passed with acceptable remnant lives, with the one failure being removed from service without significant impact on production.

Summary of results from 2008 and 2010 inspection and corresponding Level 3 results on the 5 worst anomalous elbows

FFS CASE STUDY 3