Pipe Stress Analysis

Purpose: This document has been prepared to provide instruction and information on how South East Water (SEW) achieves the design life of its assets through prudent corrosion control measures. While this document outlines the standards which apply to each risk control and may provide some general information and reinforcement of critical aspects of each standard, it is not intended that this document replicate technical information contained in the standards.

SA Water is responsible for operation and maintenance of an extensive network of buried pipelines. Cathodic Protection (CP) is applied to a large proportion of those buried assets which assists with the management of external pipeline corrosion and is therefore and an important asset management tool to greatly increase asset life. This Standard has been developed to assist in the design, maintenance, construction, and management of SA Water’s pipeline CP infrastructure. The purpose of this Standard is to detail the requirements for each phase of a pipeline CP project from design, construction and commissioning, to maintenance and monitoring to ensure a consistent approach is achieved independent of the delivery model of a project, its location, project ownership or other influences.

It is common practice worldwide for piping designers to route piping by considering mainly space, process and flow constraints (such as pressure drop) and other requirements arising from constructability, operability and reparability. Unfortunately, pipe stress analysis requirements are often not sufficiently considered while routing and supporting piping systems, especially in providing adequate flexibility to absorb expansion/contraction of pipes due to thermal loads. So, when “as designed” piping systems are handed-off to pipe stress engineers for detailed analysis, they soon realize that the systems are “stiff” and suggest routing changes to make the systems more flexible. The piping designers, in turn, make changes to routing and send the revised layout to the pipe stress engineers to check for compliance again. Such “back and forth” design iterations between layout and stress departments continue until a suitable layout and support scheme is arrived at, resulting in significant increase in project execution time, which, in turn, increases project costs. This delay in project execution is further worsened in recent years by increased operating pressures and temperatures in order to increase plant output; increased operating pressures increase pipe wall thicknesses, which, in turn, increase piping stiffnesses further. Such increased operating temperatures applied on “stiffer” systems increase pipe thermal stresses and support loads. So, it is all the more important to make the piping layout flexible at the time of routing.