Cracks can develop in pipelines at any stage – during fabrication, installation or throughout operational life. As such, cracking processes are complex, not always well understood and often difficult to predict. The morphology of cracking is highly variable, and there may be many anomalies present in a pipe body and seam weld that would not behave as cracks but create a crack-like indication in inspection data – creating a false picture.
Hence, it is difficult to reliably identify the different cracking types based on inspection data alone. This creates uncertainties in managing the integrity of a pipeline that is subject to cracking – in a cost-effective way. Being able to solve this problem can produce significant savings, but that solution has to embrace an understanding of the cause of cracking, inspection capabilities and limitations, data management, an understanding of field conditions, and failure pressure calculations. And that is quite a challenge.
Our integrated Crack Management Framework provides clients with a team of subject matter experts and all the elements – laboratory testing, the latest in-line inspection technology, software, consultancy and field work – required to understand, quantify and safely manage the threat of cracking along a pipeline. It is recognized that many operators may not require the entire Crack Management Framework. Its modular design therefore offers clients the option of selecting individual elements depending on their particular requirements. The framework has been developed through a consolidation of industry best practices and can be adjusted to meet local regulatory requirements and client preferences.
Root Cause Analysis
Our root cause analysis can range from diagnosing the type of cracking present on a pipeline to a full investigation of crack-induced failures. Materials and corrosion and welding experts experienced in all conceivable types of cracking are on hand to accurately diagnose the cracking type. We have years of experience completing root cause analyses and have in-house testing facilities to support investigations when necessary.
It is essential to understand where cracking would be considered most likely on a pipeline. Our susceptibility analysis service combines data sets and screens the pipeline to identify those areas at the highest threat. This data is used to drive focused data evaluation and in-field verifications, leading to the accurate identification of cracks.
Defect Critical Size
Using the chosen assessment method (e.g. API 579, BS 7910, MAT-8, ln-sec, CorLASTM), initial calculations are completed to identify a defect size that would be considered unacceptable. The output informs the minimum sizing requirements of the ILI system to locate critical cracks. It also highlights the impact of conservative assessment inputs, such as an assumed fracture toughness. This can be extended to a Critical Crack Defect Manual, which defines acceptance curves, response times and pressure reduction requirements to assist in-field decision making.
A thorough understanding of the likely nature and location of any cracking and, of course, critical crack dimensions is a key input for selecting the optimum inspection system with the best possible combination of technologies. Factors such as internal diameter changes, wall thickness changes, bend radius, cleanliness, offtakes, flow rates and pressures also need to be carefully considered to ensure that data collection is optimized, giving increased confidence in the evaluation of the inspection data.
ROSEN has the world’s most advanced and largest fleet of UT and EMAT in-line inspection tools for crack detection. These tools provide critical data on the location and size of crack-like features. More details are available here.
The highly variable nature of crack-like features makes the evaluation of the data collected by in-line inspection very complex. Close collaboration between expert data evaluators and senior integrity engineers with extensive experience in dealing with cracks in pipelines ensures credible results and that efforts are focused on the critical areas.
Immediate Crack Assessment
Following the preliminary results of an in-line inspection, ROSEN will calculate indicative defect failure pressures to ensure that immediate integrity threats are identified and prioritized. In combination with the susceptibility analysis, the results will be used to drive the assessment of sites for initial in-field investigations.
Obtaining accurate and complete in-field data is critical for supporting root cause analyses and confirming the performance of an ILI tool. On-site materials, corrosion and welding experts, working with experienced 3rd party or ROSEN NDE technicians, ensure that all data, including flaw measurements, coating condition, soil types, cathodic protection status etc. is collected in the correct manner and that all critical observations are made.
The results of in-field verification can enhance understanding of the causes of cracking and the factors driving susceptibility. Therefore, further collaboration between expert data evaluators and integrity engineers taking account of in-field findings to confirm findings and focus efforts on areas of uncertainty ensures that maximum value is extracted from the inspection data.
The results of ILI and in-field investigations will be consolidated and reported, and features will be assessed to determine their impact on the immediate and future integrity of the pipeline. A range of assessment methods will be considered and the most appropriate chosen upon client consultation. The future integrity assessment will consider fatigue and environmental (e.g. SCC) growth mechanisms where applicable. A summary of all previous activities – including root cause analyses and metallurgical testing – will be included with the results of the assessment to provide a comprehensive list of mitigation and repair actions.
To ensure a comprehensive crack management strategy, the consequence of failure must be combined with the threat of cracking to determine overall risk. We can use elements of an operator’s existing risk assessment and update it to reflect the latest data, or we can develop a completely new model. Often, a consequence assessment is completed and combined with the results of the susceptibility analysis to produce an overall analysis and report.
Crack Management Plan
This is the final deliverable of the Crack Management Framework and defines a long-term strategy for safe and reliable operation. Possible elements included may range from re-inspections, sectional recoating and operational controls to repair plans, data management and SCC direct assessment updates. Often, this plan covers 20 years of future operation, demonstrating that repeat hydrotesting is not required, the economics of crack management are recognized and remedial costs are optimized.
ROSEN has a long-term track record working with leading pipeline operators and regulators worldwide to provide advanced crack assessment services. We bring expertise in stress corrosion cracking, pipe manufacturing, fracture mechanics, inspection systems, inspection data evaluation, non-destructive examination, data analysis, fatigue, and risk and stress analysis. We merge them all together as required to support the production of a complete, detailed crack assessment.
You can benefit from our experience, technology and expertise delivered via the Crack Management Framework, which integrates all the key elements needed to take control of cracks with a robust crack management plan targeted at avoiding the need for costly and disruptive hydrotesting and ensuring safety.