Abstract

Annex C of the 2023 edition of Canadian Standard Association’s Standard Z662 includes a risk-based pressure design approach (the “safety class” approach) as an alternative to the “class location” approach which is included Clause 4. The safety class approach, like the class location approach, uses a set of hoop stress factors to calculate the minimum wall thickness from the pressure, diameter, and specified minimum yield strength.

The use of alternative hoop stress factors in the safety class approach also has implications for assessment of metal loss corrosion anomalies per Clause 10 of the standard. In Clause 10, the inverse of the maximum allowable design hoop stress factor are adopted as a minimum safety factor for allowable corrosion defects. This approach, which has been used for pipelines designed using the class location system since the 2003 edition of the Standard, was also adopted in the 2023 edition for pipelines designed using the safety class approach. Adoption of this approach for safety class designs was based on an analytical understanding of the resulting relationship between design and corrosion safety levels; however, comprehensive reliability studies were not undertaken to numerically demonstrate that it leads to adequate reliability levels for corroded pipe.

This paper is based on a joint industry project (JIP) that was formed to validate the suitability of (and, if necessary, consider refinement to) the corrosion assessment approach described in Clause 10 of CSA Z662 for safety class designs. This paper describes the validation analysis performed, which, based on the calculation of implied allowable failure probabilities, verified that the corrosion assessment approach in Clause 10 for safety class designs provides levels of safety that are comparable to those produced by Clauses 10 for class location designs. As such, no major refinements to the methodology were required. However, the JIP did identify and implement a simple change that improves safety when assessing corrosion for pipeline designs with third-party damage prevention measures that, following the safety class approach, justify reduced wall thickness.

Authors:

McAllister, Lowell; Nessim, Maher (Maher Nessim Engineering); Wang, Hong (Canada Energy Regulator); Khushoo, Nitish (Trans Mountain), Van Boven, Greg (TC Energy)

Publisher:

ASME The American Society of Mechanical Engineers
2026 International Pipeline Conference

Year Published:

2026

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