Providing Assurance against SCC on Aging Assets

In a Nutshell:

Stress Corrosion Cracking (SCC) has been described by many operators as the pipeline threat that is the most difficult to deal with due to the uncertainties of location, identification, measurement and growth rate prediction. However, it is particularly challenging if cracking is present across multiple pipeline systems and if the cracking is both axially and circumferentially orientated. Taking a holistic approach to this threat and addressing it using a framework of individual but integrated elements allows effective management of this threat.

Cracking mechanisms are complex, not always well understood and often difficult to predict. The morphology of environmental cracking is highly variable, and there may be many other features present in the pipe body and longitudinal seam weld area that, while not environmentally assisted cracking, nevertheless create similar signals in the inspection data. These challenges make it difficult to reliably discriminate different feature types based only on a single source of inspection data (probability of identification) and creates significant uncertainties in how to best manage the future integrity of a pipeline subject to environmentally assisted cracking.

Since not all parts of the system, or even sections on a single pipeline, will have the same susceptibility to SCC, it is crucial to understand the threat before proposing a solution or plan to manage this issue. Prior to defining a management strategy, operators must be able to answer questions like:

• What type or types of environmentally assisted cracking am I dealing with?
• What are the primary contributing factors, and how do they interact given the environment?
• Where is cracking most likely to occur?
• Can I quantify the risk in terms of probability and consequence for my entire system and prioritize?

A holistic approach

In order to make the right decisions on likelihood of SCC, selection of combinations of inspection tools, data evaluation strategy and defining corrective actions, it is critical that multiple factors are considered so that a robust plan potentially combining in-line inspection, direct assessment, hydro-testing and risk assessment can be developed to manage stress corrosion cracking.

In addition to providing state-of-the-art inspection tools, it is vital for vendors to close the circle by supporting operators from start to finish, assuring fit-for-purpose solutions to detect and mitigate SCC; assurance can be provided through the implementation of a holistic, partnership-based approach such as the Crack Management Framework (see Figure 1).

The Crack Management Framework provides a visual representation, based on our experience with operators worldwide, of the many elements that need to be brought together in a close collaboration between operator and vendor to effectively tackle SCC. A project typically consists of three phases:

Phase 1: Understand the threat. This means involving subject-matter experts (SMEs) of many disciplines from the start. As every pipeline or section has its specific environmental and physical properties, it is important to look into all the available information on the pipeline and surroundings. This also means that the ILI data-analysis process gets a clear scope and directive to turn data into the required information based on the pipeline’s characteristics.

Phase 2: Quantify the threat. Based on results from Phase 1, the ILI inspection is conducted, and verification of features takes place. SMEs will support the necessary analysis, detailed risk assessment and prioritization of actions.

Phase 3: Define a strategy to manage the threat. In this phase the work carried out previously is consolidated by transferring the mitigating actions into maintenance planning and developing an asset maintenance strategy to ensure safe future operations.

What you need

While, with the three phases simply laid out, it may seem that this is a step-by-step process, our long-term track record working in partnership with operators and regulators worldwide to provide advanced crack assessment services demonstrates that multiple iterations of susceptibility model, evaluation strategy and management plan that take feedback from ILI findings, in the ditch inspections and laboratory analyses make this a live and constantly developing process. Expertise in areas such as stress corrosion cracking, pipe manufacture, fracture mechanics, inspection systems & evaluation, non-destructive examination, data analysis, fatigue, stress analysis, and risk all support the framework. When merged with a full suite of state-of-the-art inspection technologies, it becomes possible to provide effective solutions using the comprehensive Crack Management Framework.

The Crack Management Framework integrates all the key elements needed to take control of cracks with a robust crack management plan aimed at limiting the need for costly and disruptive hydro-testing, recoating, or replacement, and, most importantly, at ensuring safety.