Inspectioneering
Inspectioneering Journal

FFS using 3D Structured Light and Pipeline Integrity

By Joe Pikas at Technical Toolboxes. This article appears in the September/October 2013 issue of Inspectioneering Journal

Introduction

Even though oil and gas pipelines and their related facilities are generally safer for people and the environment compared to other means of transportation, occasional leaks and failures due to corrosion and other defects have become an issue in maintaining pipeline integrity. A number of solutions have been developed for the assessment of remaining strength of corroded pipelines. There is a need in the pipeline industry to assess the severity of a particular feature (dent, gouge, corrosion pit, etc.) in a pipe or structure as to whether or not repair or removal is required. This process is now called Fitness-for-Service (FFS). It is a process to evaluate features that may impact a pipeline or other structure’s suitability for service. One tool that helps make this possible is called Phase Measurement Profilometry (PMP), also known as 3D structured light. The information this advanced technology can supply will facilitate the determination of a need for repair and prioritization of defects for remaining-life assessments of pipeline segments to meet today’s stringent industry and regulatory requirements.

This article will provide the pipeline industry with an understanding of the differences between “screening tools” and “prove up tools,” as well as the benefits of the 3D structured light technology (accuracy, repeatability, reliability and cost), to meet API 579/ASME FFS-1 standards and PHMSA regulations.

Knowledge, Verification/Prove Up of the Pipeline or Structure

Fitness-for-service has been used in the oil and gas industry since the early 1980’s. On the petroleum side, it was always known as FFS, while the gas pipeline side knew it as ASME B31.G. In 2007 the American Petroleum Institute (API) and American Society of Mechanical Engineers (ASME) published a joint standard entitled API 579/ASME FFS-1.

This standard consists of the following three levels for assessing corrosion:

  • Level 1 – Quick evaluation with the minimum number of measurements (maximum depth and length) and a built-in large safety factor (ASME B31.G).
  • Level 2 – Additional measurements and more in-depth analysis to establish a remaining strength of corroded pipe (Modified and RSTRENG).
  • Level 3 – Intensive analysis with measurements using tools such as the 3D Toolbox - Phase Measurement Profilometry (PMP), loading stresses, stress strain and material understanding to conduct a finite element analysis (FEA).

Because of the errors that may be introduced using mechanical measurement instrumentation (pit gauges), a Level 3 analysis was rarely conducted. The field data was too inconsistent or too difficult to measure due to the complexity of the defects and features.

Feasibility factors for selecting a FFS level for analysis of a corroded area include:

  • Quantity of data available with which to perform an evaluation
  • Quality of the data
  • Degree of significance of the analysis to the pipeline operations
  • Degree of significance of a specific corroded area in the remedial plan for all anomalies in a line section being investigated

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