Offshore Field
Project:
Hydrogen Induced Cracking Evaluation
Overview
Hydrogen Induced Cracking (HIC) is the development of internal cracks in low strength steels in a sour environment (Hydrogen sulphide and water). HIC is a particularly challenging, time-dependent cracking mechanism from an integrity management perspective due its embrittling effect on carbon steel leading to reduction in material toughness and the unpredictable nature of its propagation.
Location
Classified
Background
Reference:
The study considered a large quantity of offshore pipelines across five fields. Over 50 of the multiphase production and gas-lift pipelines are in sour service and associated with a credible threat of HIC.
Frontline Integrity has extensive proven track-record of supporting operators to successfully manage pipelines with complex cracking threats. They were asked to undertake a per pipeline threat ranking and generate a pipeline integrity action plan to support risk management activities. No direct crack inspection of any of the lines had been undertaken to date, meaning that the threat had to be evaluated based on other available datasets.
The approach
Four interrelated work areas were combined to feed into the threat assessment and action plan:
- Detailed interrogation of in-line inspection (ILI) signal data and tool performance capabilities to identify evidence of potential HIC damage in historical metal loss data sets (laminations, blistering and internal pitting.)
- Examining the proximity to failure of potential HIC damage using API 579 Part 7 and 9 fracture mechanics and fatigue assessment.
- Developing a HIC susceptibility model based on latest industry best-practice to score each pipeline for operational duty, materials of construction and existing HIC indictors.
- Generation of critical flaw envelopes for future laminations found by ILI to expedite anomaly response.
Results
Frontline used its practical multi-disciplinary experience of HIC management to achieve a clear threat differentiation between pipelines. An iterative risk-management plan was formulated for the highest risk pipelines and integrated into the operator’s risk-management plan for the pipelines. Its primary purpose was to address potentially ‘critical’ anomalies in high-susceptible pipelines as well as collect improved threat data to refine the model. Recommendations were implemented across the following key areas:
- Collection of more detailed operational data on fluid composition to improve pipeline differentiation.
- Collection of improved material property data across the system to better quantify the effects of hydrogen embrittlement on the resistance to hydrogen induced cracking (HIC).
- Targeted external close visual inspection of potentially ‘critical’ anomalies exhibiting HIC-like characteristics.
- ILI crack detection where an extensive HIC-like anomaly population is present.
- Rectification of key locations of additional loading which could accelerate HIC damage i.e. freespans, locations of pipeline movement and high riser hydrodynamic loading locations.
- Advanced Level 3 finite element analysis (FEA) analysis on a number of locations that failed the API Part 9 Level 2 analysis to quantify which areas data collection should be targeted to improve future assessment results.
