R2 location class

Location class R2 (rural residential) has potential to be mis-applied, although I suspect that many people don’t realise it.  Let me illustrate with a comparison of two very different pipelines, both with MAOP 10.2 MPa:  DN 100 (common supply to small towns) and DN 1050 (now being designed en masse in Queensland).  The “measurement length” is about 100 m and about 1000 m respectively.

The key part of the R2 definition is the reference to “single residence blocks typically in the range 1 ha to 5 ha”.  If the blocks are square then they would be have sides of 100 m to 225 m.  Our DN 100 pipeline though such an environment would at worst affect one or two houses if it was to suffer a full bore rupture, and may well affect none.  You would be pretty unlucky to have any injuries or fatalities among the residents unless the pipeline happened to be very close to a house at the point of failure.

On the other hand the DN 1050 pipeline could conceivably have a couple of hundred houses within the measurement length (if the blocks are the minimum 1 ha), or more realistically might have a few dozen houses if the blocks are 5 ha.  Either way the consequences of a full bore rupture would be much more serious than failure of the little DN 100 pipeline in a T1 (suburban area); multiple fatalities and many injuries seem possible.

To me this looks inconsistent.  The examples are at the extreme ends of the range but serve to illustrate the point.

It’s also worth thinking about the note at the end of the R2 definition (AS 2885.1 Clause 4.3.4(b)):

NOTE: In Rural Residential societal risk (the risk of multiple fatalities associated with a loss of containment) is not a dominant design consideration.

This reinforces my view that it doesn’t seem right to apply R2 to a situation where pipeline failure can result in multiple fatalities.

For a couple of projects I’ve suggested that the R2 definition be interpreted conservatively so that R2 is applied anywhere there are more than a dozen or so houses within the measurement length, regardless of lot size.  So for the DN 1050 pipeline the lot size within the preferred R2 area may be substantially larger than 5 ha.  Conversely, for small pipelines (our DN 100 example) one could quite defensibly decide that R2 doesn’t apply for lot sizes larger than say 1 ha, and even that is quite conservative.

I’m not suggesting that the 1-5 ha guideline is redundant, but rather than it be applied with some thought about how many houses might actually be affected by a pipeline failure.

Having said all that, the design rules for R2 are not very different to those for R1, yet again reinforcing the view that R2 areas are not expected to have potential for really serious failure consequences.  I think the main value in assigning R2 location class (or any location class for that matter) is in helping the participants in the safety management study appreciate the general magnitude of consequences if the worst should happen.

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One Response to R2 location class

  1. Mark Coates says:

    Good points Peter.

    One of the requirements when determining the location class is the potential affected area due to a rupture (the measurement length), and determine the potential impact – so as previously stated, maybe the location class should be determined by first analysing the impact area. Although location classification is based on predominant land use, the measurement length may qualify it to be raised to a more severe location class – A DN1050 pipe zone may be classified as T1 with a larger house spread than a DN100 R2.

    The processes detailed in AS2885.1 cover increasing the location classification if situations within the land use are more severe – such as an increase in measurement length.

    Secondary location classes may also have an affect on designation.

    Also note that thin-walled larger bore pipelines are more susceptible to fracture propogation, and this should be taken into account when determining impact zone and zone classification. A DN100 may have a local failure, whereas the DN1050 may result in a propogating failure (if not correctly mitigated).

    Thanks

    Mark C.

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