Prequalified design

(I’ve been quiet for a fortnight – a week ago we had a DIY country wedding and reception for my daughter and that meant several frantic but joyful days with no time for anything else.)

Late last week I ran a safety management study workshop for what was probably the most low-risk pipeline I’ve yet been involved with – barely 2 km of DN 150 in a remote and unpopulated area.  I suggested to my client that they consider using the prequalified design permitted by Clause 5.6 of AS 2885.1, and thereby save themselves the time and cost of the workshop.  However it turned out that this particular pipeline didn’t quite meet the criteria for prequalified design so we proceeded with the workshop anyway.

The reason for including the prequalified design in AS 2885 was to minimise the design and project management overhead on very small projects.

I’d be interested to hear whether pipeline designers are in fact making use of it.  So please post a comment if:

  • You’ve used the prequalified design provisions in Clause 5.6
  • You’ve considered using them but found they weren’t suitable (and why)
  • You have other views on the usefulness or otherwise of Clause 5.6
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3 Responses to Prequalified design

  1. Michael Malavazos says:

    Would be interested to see whether others have utilised this section of the standard as well. Once we referred a licensee to it thinking that it would be appropriate for their proposed project which entailed a relatively low pressure oil production but after closer consideration the licensee came back that it could not utilise s.5.6 as their project did not meet all the conditions. Look forward to seeing others comments and interested to see if we have set the bar too high.

  2. Liz Brierley says:

    In Adelaide Envestra own a Class 150 Pipeline network. The prequalified pipe wall thicknesses were significantly higher than what was used in the network, based on carrying out full calculations. I found that the standard didn’t give enough background on the basis for the prequalified wall thicknesses to understand why there was such a difference.

    • petertuft says:

      Liz,

      One can only write so much in the standard itself. There is an Issue Paper that goes into it in some detail but there are currently some intellectual property issues in making those generally available. In a nutshell, quite a lot of work was done on selecting minimum wall thicknesses to meet “No Rupture”, penetration resistance and release rates.

      It is certainly a very conservative design, but then it needs to be to bypass so much of the design process. For short simple pipelines the savings in engineering costs may outweigh the extra steel but I’m not aware that anyone has ever worked out what the typical break-even point might be – would be an interesting exercise.

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