Methodology to Develop Fitness-for-Service Assessments for Crack Detection In-Line Inspection Data

Abstract

Implementation of Integrity Management Programs (IMP) for pipelines has motivated the design of Fitness-For-Service methodologies to assess Stress Corrosion Cracking (SCC) and fatigue-dependent features reported by Ultrasonic Crack Detection (UTCD) In-Line Inspections. The philosophical approach defined by the API 579 [1] “Fitness-For-Service” from the petrochemical industry in conjunction with Risk-based standards and regulations (i.e. CSA-Z662-2003 [2] and US DOT 49 Parts 192 [3] and 195 [4]) and in-line inspection validation (i.e. API 1163 [5]) approaches from the pipeline industry have provided the engineering basis for ensuring the safety, reliability and continued service of the in-line inspected pipelines. This paper provides a methodology to develop short and long-term excavation and re-inspection programs through a four (4) phase-process: Pre-Assessment, Integrity Criticality Assessment, Remediation and Repair, Remaining Life Extension and In-Service Monitoring. In the first phase, Pre-assessment, areas susceptible to Stress Corrosion Cracking (SCC) and fatigue-dependent features are correlated to in-line inspection data, soil modeling, pipeline and operating conditions, and associated consequences in order to provide a risk-based prioritization of pipeline segments and technical understanding for performing the assessment. The second phase, Integrity Criticality Assessment, will develop a short-term maintenance program based on the remaining strength of the in-line inspection reported features previously correlated, overlaid and risk-ranked. In addition, sites may be identified in Phase 1 for further investigation. In the third phase, a Remediation and Repair program will undertake the field investigation in order to repair and mitigate the potential threats as well as validating the in-line inspection results and characterization made during the Pre-assessment and Integrity Criticality Assessment (Phases 1 & 2). With the acquired knowledge from the previous three (3) phases, a Remaining Life Extension and In-Service Monitoring program will be developed to outline the long-term excavation and re-inspection program through the use of SCC and Fatigue crack growth probabilistic modeling and cost benefit analysis. The support of multiple Canadian and US pipeline operating companies in the development, validation and implementation of this methodology made this contribution possible.

Non-destructive techniques for corrosion detection: A review

“…The penetration depth can be increased to sub-surface regions by using low-frequency ECs (LFEC), usually ranging from 100 to 50 Hz. 95 The standard depth of penetration (δ) is defined as the distance below the surface of a flat specimen at which there is 37% EC charge density on surface. The standard depth of penetration is inversely dependent on magnetic permeability (M), electrical conductivity (T) and the frequency generated by the coil (f) and can be expressed as in the below equation, 31 EC technique can detect cracks, inclusions, porosity and corrosion.…”

“…As mentioned earlier, LFEC are used to determine the defects in the underlying structure. 95 Remote-field EC (RFEC) was developed widely to inspect defects on pipes and tubing. 99…”

“…As mentioned earlier, LFEC are used to determine the defects in the underlying structure. 95 Remote-field EC (RFEC) was developed widely to inspect defects on pipes and tubing. 99 RFEC consists of two coils offset by two pipe diameters, usually operating at a minimal frequency such that the electromagnetic field is transmitted through the entire pipe thickness.…”