Yearly Archives: 2018

21 09, 2018

How to Perform Quantitative Risk Analysis for Transmission Pipelines

Quantitative risk analyses are used in the pipeline industry to identify high-risk locations and main contributing threats; to evaluate risk against an acceptance criterion; to evaluate changes in risk over time; to guide integrity management decisions; and to demonstrate regulatory compliance. We developed for the U.S. Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) guidelines for the development and application of pipeline quantitative risk analysis models for natural gas and hazardous liquids transmission pipelines. The purpose of these guidelines are to: Assist operators in developing new models and in identifying and addressing [...]

20 09, 2018

How to Improve Corrosion Assessment Using Reliability-based Criteria

Corrosion assessment criteria in current standards for onshore transmission pipelines rely on safety factors that are experience-based, with unknown implications on the risk or safety level associated with the pipeline. Working as part of a joint industry project, we have developed reliability-based corrosion assessment criteria in a deterministic format that are calibrated to achieve a specified safety level. The main features of the criteria are: Inclusion of calibrated safety factors and input parameters that result in intended reliability levels within a specified tolerance; Consideration of two failure modes: burst and small leak; and Easy-to-use [...]

17 09, 2018

Does Feature Length Growth Affect Predicted Burst Pressure in Pipelines?

The pipeline industry has established various methodologies to estimate corrosion growth in pipelines. However, growth of corrosion feature length is inconsistently addressed in these methods. We worked with Enbridge Pipelines to review these methodologies and determine the impact of feature length on corrosion burst pressure predictions. This review: Considered methodologies that are applicable to both feature lengths and depths; Evaluated the ability to use the methodologies to identify unsafe defects using estimated burst pressure from repeated in-line inspections; and Compared findings with feature depth only analysis to understand the impact of feature length on [...]

17 09, 2018

How to Analyze Angled Cracks in Spirally Welded Pipelines

Spirally welded pipelines (extensively used in liquid transmission pipeline systems) may contain manufacturing anomalies that are susceptible to fatigue growth. To account for the angle of these cracks, with respect to the longitudinal pipe axis, modifications to inputs of crack assessment models are required. Using the widely-used pipeline assessment model CorLAS®, we worked with Enbridge Pipelines to investigate two input modifications: Consideration of the normal stress component perpendicular to the angled crack, for which we developed a stress transformation calculator; and Using an effective crack length calculated as the longitudinal projection of the full [...]

17 09, 2018

How to Apply Limit States Design Checks to Geotechnical Loads

A limit states design approach has been developed for geotechnical loads using a strain-based design format. This approach addresses the high level of uncertainty associated with the loading processed, which has limited the availability of design guidance in the past. Working as part of a joint industry project, we have carried out a project to calibrate risk-consistent limit states checks that can be used for a range of strain demand and capacity distributions applicable to geotechnical loads. The project: Developed checks for local buckling and rupture; Defined criteria for selecting the characteristic strain demand [...]

14 09, 2018

Does Reliability-based Corrosion Assessment Criteria Reduce Risk?

Corrosion mitigation for pipelines, vintage pipelines in particular, has a significant effect on the industry’s management systems and related costs. To help optimize the corrosion management process, deterministic reliability-based corrosion assessment criteria have been developed for onshore pipelines as part of a joint industry project. We worked with TransCanada Pipelines to evaluate the assessment criteria to determine if they lead to reasonable corrosion management decisions and compare well to other deterministic and probabilistic criteria. The evaluation involved applying the criteria to 22 transmission pipeline cases and comparing the results to: CSA Z662's deterministic criteria; [...]

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