Inspection inevitably forms an integral part of any pipeline integrity management system (PIMS). There are many inspection techniques available to operators, though no single inspection technique is appropriate for every application.
Performing pipeline inspection may be the single greatest cost associated with pipeline operation and can therefore have a significant impact on OPEX. Selecting an appropriate inspection method and defining an optimal inspection interval is therefore critical for budgeting purposes, as well as for assessing the current and future pipeline integrity.
This article takes a brief look at the use of internal (inline) and external inspection techniques that may be used when assessing pipeline integrity.
Pipeline Integrity Assessment
Pipeline integrity management should start at design and continue through to decommissioning. The objective of a pipeline integrity management system is to ensure that a pipeline can continue to transport fluids safely throughout the life cycle of the asset without causing harm to life, the environment or the business.
Within the operational phase of the pipeline life cycle, integrity management plans may be developed by adopting a risk-based inspection (RBI) approach. RBI planning allows targeted inspection of high-risk assets and hence optimizes resource allocation and scope for risk reduction.
Following risk assessment, an integrity assessment of the highest risk assets may be performed to review the threats in more detail. There are three commonly recognized methods for assessing pipeline integrity:
- Inline inspection (ILI);
- Pressure test; and,
- Direct assessment.
More than one method may be required to enable all threats to be adequately assessed, though in some cases none of the methods may be appropriate and focus should instead be drawn on prevention measures.
A discussion of inline inspection and direct assessment methods is provided below. Pressure testing as a means of assessing integrity is not discussed as part of this article, though caution is advised when using this method to understand its risks and limitations, including potential for pressure reversals and inability to fail pit-like defects.
An intelligent pig is a tool that is able to detect, locate and characterize pipeline anomalies as it transits the pipeline, driven by the product flow. This inspection technique is referred to as inline inspection, or ILI. One of the key benefits of ILI is the ability to continue production during the inspection. However, as with any pigging operation, ILI requires careful planning in order to minimize the risk of the tool becoming stuck as it transits the pipeline.
The are many types of ILI techniques available and selection of the appropriate technology will depend on the threat being assessed. An overview of some common pipeline threats that can be assessed using ILI and the relevant inspection technologies is provided in Table 1.
Table 1: Overview of ILI Technology
Direct assessment is commonly used when conventional ILI or pressure testing is not feasible or practicable. Direct assessment is a recognized method of determining pipeline integrity based on the threat of internal corrosion (ICDA), external corrosion (ECDA) or environmental cracking, e.g. sulphide stress cracking (SSCDA). The details of the process vary depending on the threat being assessed but the general procedure remains unchanged:
- Data collection
- Indirect inspection
- Direct examination
Indirect assessment involves a review of all available data to predict where corrosion, or environmental cracking, may occur. Subsequent verification is then performed via direct examination, i.e. inspection, at those locations. For example, external corrosion is most likely to occur in an area of CP under-protection and hence direct examination locations would be selected based on CP survey data where the measured pipeline potential is below critical limits. An overview of some of the inspection techniques that may be used is provided in Table 2.
Table 2: Overview of External Inspection Technology
The inspection techniques referred to in Table 1 and Table 2 are not definitive or exhaustive. Every inspection technique has its own advantages and disadvantages and these should be clearly understood before selecting the inspection techniques. Furthermore, there are many less common inspection techniques that may be appropriate depending on any inspection constraints that may be applicable.
AIE is able to offer expert support in all aspects of pipeline integrity management, including pipeline RBI and integrity assessment.
AIE’s inhouse RBI software, Veracity Pipeline, provides operators with a user-friendly and systematic approach to pipeline RBI planning, which forms an integral part of pipeline integrity management. The software enables operators to assess and understand risks affecting their assets so that data-driven decisions can be made to optimize inspection, monitoring and testing activities associated with ongoing pipeline integrity management.
Our multi-disciplined team of engineers are able to use their knowledge of industry best practices to provide the highest quality pipeline integrity assessments to provide our clients with accurate remaining life predictions and recommended responses to key assessment findings.
AIE’s services also include project management of inspection activities, from selection of appropriate inspection techniques to managing onsite execution.