At the recent Member’s meeting, INEOS O&P invited the team from ROSEN UK to present an overview of a project that had been carried out that showed how crack susceptibility analysis is a critical aspect of pipeline integrity management.
The presentation highlighted how their analysis helps identify potential threats and mitigates the risks associated with cracking mechanisms, which could lead to pipeline failure if left unchecked. This blog delves into the significance of their crack susceptibility analysis, common cracking mechanisms, and insights from a case study conducted on an INEOS pipeline.
What is Crack Susceptibility Analysis?
Crack susceptibility analysis is a process that assesses the likelihood of cracks forming in a pipeline. This evaluation considers various factors, including pipeline material, operational conditions, and external influences. By analysing these elements, engineers can implement proactive measures to prevent failures and enhance pipeline safety.
Common Types of Cracking Mechanisms
Pipeline cracks can originate from different sources. The key cracking mechanisms for the majority of onshore pipelines include:
- Hydrogen-Induced Cracking (HIC) – Caused by the absorption of hydrogen into the metal, leading to internal pressure buildup and crack formation.
- Stress Corrosion Cracking (SCC) – Arises due to the combined effects of tensile stress and corrosive environments.
- High pH SCC: Typically found in gas pipelines with long-term sustained stress.
- Near-neutral pH SCC: More common in liquid pipelines with aggressive pressure cycling.
- Fatigue Cracking – Develops due to repeated stress cycles, leading to progressive material degradation.
- Weld-Related Cracks – Includes heat-affected zone (HAZ) fatigue cracks and lack-of-fusion defects.
- ERW Hook Cracks – Occurs in electric resistance welded (ERW) pipes due to manufacturing imperfections.
Distinguishing Crack-like Anomalies and the Importance of Susceptibility Analysis
Inspection tools frequently detect anomalies that resemble cracks, but many of these do not represent true cracks or pose a threat to pipeline integrity. A true crack, as defined by ASME, is a narrow flaw caused by mechanical separation. However, many anomalies may appear ‘crack-like’ without posing a threat to pipeline integrity. Accurately identifying which anomalies are real cracks—and which are not—is essential to avoid unnecessary interventions and ensure that real risks are properly managed.
Since inspection tools such as Non-Destructive Evaluation (NDE) and In-Line Inspection (ILI) have limitations in distinguishing between benign and integrity-threatening features, susceptibility analysis plays a crucial supporting role. This type of assessment evaluates cracking threats that may impact a pipeline based on factors such as pipeline material, operating conditions, and environmental exposure. By doing so, this:
- Helps prioritise pipeline sections for inspection and intervention.
- Supports the development of a targeted integrity management plan.
- Enhances overall pipeline safety and longevity.
Case Study: INEOS Crack Susceptibility Analysis (Blackness to Grangemouth Pipeline)
A recent susceptibility analysis was conducted on a 12-inch natural gas pipeline running from Blackness to Grangemouth (12BLAGRA). The pipeline, constructed in 1999 with API 5L X60 grade ERW line pipe, spans 12 km and operates at a maximum allowable pressure of 85 bar.
Scope of the Study
The analysis assessed susceptibility to:
- Fatigue Cracking – Evaluated using pressure cycling data.
- Stress Corrosion Cracking (SCC) – Considered external factors like coating conditions, operating stress, and environmental influences.
- Hydrogen Embrittlement – Investigated due to cathodic protection (CP) overprotection.
Key Findings
- Stress Corrosion Cracking (SCC): The analysis found a low susceptibility to both high pH and near-neutral pH SCC, thanks to the pipeline’s high-performance external coating, low operating stress, and absence of compressor stations.
- Fatigue Cracking: Based on a three-year pressure cycling analysis, the pipeline exhibited low susceptibility to fatigue cracking.
- Hydrogen Embrittlement: The pipeline showed a potentially high susceptibility due to CP overprotection, with survey data indicating OFF-potentials exceeding -1200 mV.
Recommendations for Mitigating Crack Susceptibility
The following actions were identified to improve pipeline integrity and reduce future risk from cracking:
- Monitor Axial Loading – Reassess circumferential SCC susceptibility if there is evidence of axial loading on the pipeline.
- Improve CP Monitoring – Install AC-sized potential measurement coupons at all test facilities on 12BLAGRA where dc coupons are not installed.
- Inspect Coating Condition – Conduct regular coating condition assessments at areas of overprotection to detect potential hydrogen embrittlement risks.
- Review Operating Conditions – Reevaluate the susceptibility analysis if there are significant changes in operating pressure, temperature, or pressure cycling patterns.
Crack susceptibility analysis provides pipeline operators with valuable insights into likely cracking threats that may impact their pipeline. Rather than relying solely on inspection results, this assessment can assist in determining whether a crack-specific In-Line Inspection (ILI) is necessary, based on factors such as material properties, operational conditions, and environmental influences. In the case of the INEOS pipeline, the study highlighted areas where additional monitoring may be beneficial and others where cracking concerns are minimal, which enables a more focused and efficient integrity management approach.
For more insights on pipeline integrity and risk management, stay tuned for future updates!