Road Crossings

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References:
AS/NZS 2885.1 Cl 5.2.3 Required Wall Thickness, 5.2.9 Wall thickness summary, 5.7.3 Stress due to normal loads .
AS/NZS 2885.1 Appendix G External Loads


Would the use of standard wall line pipe be ok at road crossings under the new stress rules for a new PL or should it be eliminated as not ALARP during SMS?

Pipe wall thickness is determined by multiple factors of which stress is only one (see Clauses 5.2.3 and 5.2.9).

Firstly, "standard" wall pipe may or may not comply with the stress limits in Clause 5.7.3 depending on the design factor and the details of the crossing design (cover, loads, etc) - you just have to do the calculations. The limit for combined stress is 90% SMYS, and if the design factor is 0.8 then there is a margin of only 10% SMYS to accomodate the external loads. A lower design factor gives more headroom for non-pressure loads.

Secondly, whether or not the design is ALARP doesn't have much to do with the stresses. At a road crossing it usually relates mainly to external interference protection. This is particularly significant at road crossings because they are public places where there can be lots of other infrastructure in addition to the road itself and that infrastructure attracts third party activity. Historical incident data confirm that roads are one of the most likely places for external interference incidents. So you need to identify all relevant threats and assess the protection against them

It has always been good practice to use increased wall thickness at road crossings for multiple reasons, including those above and possibly others such as a de facto increased corrosion allowance given the difficulty of repairing pipe under a road.

(Peter Tuft)