Integrity Assessment Of Non-Piggable Pipelines

Non Piggable Pipelines

A pipeline may be non-piggable because of extreme bends, changes in diameters or not desiged for pigging operation. Generally, pipeline safety regulations require the operators to ensure that the pipelines under their governance are well maintained and in a fit for purpose state. Pipeline inspection coverage includes external and internal inspection. Conventionally, pipeline inspections are carried out through non-destructive testing, using in line inspection (ILI) techniques, such as MFL or UT pigs. However, inspection on non-piggable pipelines can be challenging where ILI is not applicable.

Many of these non-piggable or challenging to pig pipelines do not have a corrosion control strategy and the technical integrity of most is unknown. This could be highly risky to operating companies as it may possibly lead to loss of production, costly failure/ degradation including environmental and safety risks, if not properly assessed. Hence, integrity assessment of non-piggable pipeline is indeed essential to maintain and ensure risk free-operations.

Focusing in this area, IEV in collaboration with Sonomatic, offers pipeline integrity assessment, using direct assessment (DA) method suited for non-piggable pipelines. DA is a structured multi-step evaluation method following the NACE standards, to examine and identify the potential problem areas relating to internal and external corrosion, including stress corrosion cracking defects. It may provide an effective alternative, equivalent to ILI and hydrostatic pressure testing for evaluating a pipeline’s integrity. This assessment method would be ideal for pipelines under the following conditions:

  • Where ILI or hydrostatic pressure testing cannot be used.
  • To avoid impractical, costly retrofitting of a pipeline.
  • To avoid shutdown/ interruption on pipeline operations.
  • Where sources of water for hydrostatic pressure testing are scarce, and where water disposal may create problems.

A desktop pre-assessment and indirect inspection based on data review via pipeline inclination profile and flow modelling analysis is conducted to identify specific locations or “hot spots” where the likelihood of corrosion damage could be most severe along the pipeline. These locations are ranked and prioritized for direct examination at site.

Two subsea external inspection technologies, namely InspeCT and UT Mapping, are employed to map wall thickness at hot spots depending on pipeline diameter and need to remove weight coat. A ROV-deployed system called ROV-iT is used to deployed these inspection systems. Diver-deployed systems are also available for pipelines in shallow water depths. The removal of weight coat and corrosion coatings is required for UT mapping at the areas of interest via ROV-iT scanner.

Data gathered from DA are used in the post assessment for Fitness for Service (FFS) and Safe Working Pressure Calculations using ASME B31G, DNV-RP-F101 and Kastner Method for the pipeline concerned, including Finite Element Analysis (FEA) if required. The remaining life assessment and recommendations for re-assessment intervals in this inspection also facilitates better informed decision makings in the overall integrity management of the pipeline.

With an extensive track record, using qualified and experienced pipeline engineers and skilled technicians, a complete solution, from engineering study to advanced inspection methodologies is offered to assess integrity of non-piggable or challenging-to-pig pipelines for re-certification purposes.

Please refer to Advanced Inspection Solutions for more information on the above-mentioned. Case studies are also available upon request.

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