To quote directly from the Code of Practice (CoP);
“The first and preferred mechanism is called the “prescribed design” and uses a series of formulae and tables derived from theoretical considerations and industry practice.
The second mechanism is called the “fit-for-purpose design” and relies on a study of a real and present situation and the use of rigorous risk assessment process to derive one or more of the factors used in the Prescribed Design case.”
It is this second mechanism that offers the opportunity for pipeline designers to utilise specific data and advances in PE100 resin properties to design more efficient pipelines.
Fit-for-purpose design is subject to the conditions detailed for MAOP and design pressure as well as the design factors set out in the prescribed design section.
The process requires a detailed risk and engineering assessment and must be reviewed by a competent designer or assessor.
The design factor assessment requires specialist evaluation skills calling on involvement from – amongst others – resin manufacturers and experts, construction personnel, designers, and process engineers.
An example of where fit-for-purpose design could be utilised is given in the CoP which describes the use of extra test pressure data on the PE100 resin for use at higher temperatures.
Using the resin manufacturer’s pressure test data at high temperatures allows a designer to apply the performance of the specific PE100 resin being used in pipe manufacture.
This gives designers capability to optimise pipeline design for the desired temperature and lifetime and may allow a reduction in pipe wall thickness and material usage.
Other areas where fit-for-purpose design could be considered include addressing the risk of mechanical damage to the pipeline by first or third parties.
This may require a design which offers greater contingency in terms of depth of installation, adjusted design factors or assessment of the contingency built into the PE100 resin performance.
The last of these considerations to be mentioned here includes assessing the PE100 resin’s resistance to slow crack growth.
This data is available from resin manufacturers and experts.
With a well-defined approach, it may offer greater contingency in designing the pipe network when using harsh installation techniques, such as trenchless, as well as eliminating a need for soil sieving for trench installation.
There are exclusions that apply to the fit-for-purpose design method.
As the CoP states “There is an overarching requirement that the use of the “fit-for-purpose” case is not to be used in any way which would compromise the safety of people, plant or the environment”.
However where there is the opportunity to use the fit-for-purpose design method, working with resin manufacturers and experts, pipe manufacturers, construction personnel, designers, and process engineers offers pipeline designers the ability to optimise the performance of their gathering lines and maximise the efficiency of the design.
You can access the APGA CoP at www.apga.org.au/apia-code-of-practice-for-upstream-pe-gathering-networks-in-the-csg-industry