Tutorial 2 - A Risk-Consistent Safety Class System for Onshore Pipelines (WG 2)


The class location system originated in the ASME B31.8 Standard as a basis for wall thickness design of gas pipelines. CSA adopted the system for gas pipelines and later expanded its application to all service fluids within the scope of the Z662 Standard. In the current version of Z662, the class location is treated as a proxy for the severity of failure consequences and is used throughout the Standard in clauses dealing with design, construction, operations and integrity management. This approach has a number of limitations that have come into focus over the past few years, including absence of environmental damage as a potential contribution to failure consequences, inconsistencies in how different service fluids are addressed and lack of transparency regarding the resulting safety levels. The Z662 Technical Committee initiated a Class Location Task Force (CLTF) to address these limitations and the CLTF initiated an effort to develop an alternate risk-consistent safety class system that can serve as a potential replacement for the class location system. Apart from being a rational alternative to the class location system, the safety class system provides a simple approach to define standardized reliability targets that can be used to support a wide range of pipeline assessments and decisions.


This tutorial will familiarize attendees with the recently developed safety class system and its potential application within the Z662 Standard and as an independent tool to support reliability-based assessments.


  • The class location system – origins, applications and limitations.
  • The risk-based approach to decision-making.
  • Defining risk and reliability targets – the code benchmarking approach.
  • Failure consequence models for various service fluids.
  • Reliability targets and their use as a basis for a risk-consistent safety class system.
  • Application of the safety class system within the Z662 Standard and as an independent tool for reliability assessments.