New toughness requirements in AS 2885

One of the less obvious changes in the recent revision of AS 2885 Part 1 was the inclusion of a requirement that almost all pipe must have a minimum toughness of 27 J, corresponding to the toughness required if API 5L PSL 2 is specified.

Clause 3.4.4 on fracture toughness was rewritten in this revision.  It clarifies the toughness requirements for station pipe, linepipe and pipeline accessories.  There were also some minor corresponding changes in Clause 4.8 that I won’t dwell on here.

For linepipe, Clause now requires that if a fracture control plan is required it must specify a toughness of not less than 27 J, even if fracture control calculations would allow a lower value.  There are only two conditions where the 27 J minimum does not apply, because there is no need for a fracture control plan at all:

  • Pipe < DN 100 AND wall thickness < 6.1 mm AND design pressure < 10.5 MPa
  • Pipe carries stable liquid with minimum design temperature > 0 deg C

The other changes in Clause 3.4.4 now provide clearer guidance on fracture control for stations and accessories.

This entry was posted in Pipeline design, Standards. Bookmark the permalink.

14 Responses to New toughness requirements in AS 2885

  1. Simon says:

    Thanks Peter,
    One debate we have had here in the office a couple of times over the last few years though relates to the major barrel on a pig reciever / launcher. They are treated as part of the pipeline not the station piping so we can’t bring them under the likes of AS4041 or B31.3. The pig traps are treated as pipeline assemblies but do we or don’t we specify a minimum Charpy toughness on the pipe as part of that assembly? Our lower design temperature in NZ is never above 0C. We have ended up defending our interpretation either way depending on the design.

  2. petertuft says:

    Unless I’ve misunderstood your question I think it should be answered by Clause in the new AS 2885.1, which covers pipeline accessories such as scraper barrels. Regardless of whether the temperature is above or below 0ºC you do need to specify a minimum toughness. Since your design minimum temp is less than 0ºC you can (must) use AS 4041 or ASME B31.3 to determine the toughness, even though the rest of the scraper assembly design may be based on AS 2885 rather than the piping codes.

    • Adam Gifford says:

      On this subject. I believe that clause is a little confusing. It is clear that minimum toughness is required for above 0degC but when the design temp is below 0deg C and AS4041 or B31.3 is used, these standards may actually exempt the material from impact testing if the wall thickness is not too thick. The way I intreprety clause is that minimum tougness is still required below 0degC and using B31.3 as an example, the toughness would need to meet table 323.3.5 (even though B31.3 would not require it) however I can see some people thinking that if AS4041 or B31.3 exempt the material from impact testing then there are no toughness requirements below 0degC.

      • Adam Gifford says:

        I should also add that if the intention of clause is to specifiy minimum toughness regardless of minimum temperature, this contradicts clause note 1 which states that fracture control may be demonstrated by compliance with AS4041 or B31.3. Again, these codes may exempt the material from impact testing in many circumstances.

      • petertuft says:

        I don’t claim expertise in the piping standards so will need to look into this, if time permits.
        As a general comment, I think the principle here is that it is good practice for all pipe to have some minimum level of toughness and the standard was trying to capture that without being too onerous. However I realise that the toughness testing requirement itself may be considered onerous in some cases, regardless of the toughness value specified.
        There have been concerns in the past about use of ASTM A106 pipe for pipeline assemblies that can get fairly cold. I’m not expert in materials but my understanding is that A106 is intended for use in moderately high temperature service and does not necessarily have the fine grain structure that gives appropriate toughness for temperatures well below ambient. I believe the standard is trying to minimise inappropriate use of such materials.

      • Lynndon Harnell says:

        I did have a circumstance where I was forced into specifying Charpy testing to AS2885 on A106B and it failed dismally. As you say it should be to AS4041/B31.3 requirements.

  3. Chris Hughes says:

    The purpose of the minimum Charpy value calculated for the Fracture Control Plan is to ensure that a running ductile fracture, once initiated, can be arrested before it travels past the initiating pipe (or, in R locations, before it travels more than 2 pipes either side of the initiating pipe). Scraper trap barrels are never more than a few metres long and any ductile fracture which initiates in a scraper barrel cannot travel more than a couple of metres before it will be arrested by a heavy component such as a valve, a flange, the closure, and probably the reducer as well. So specifying a minimum Charpy for these components based on the Battelle equation or the two-curve method is pointless.

    • petertuft says:

      That’s true, and the standard doesn’t talk about specifying a minimum toughness calculated by the methods you mention. The minimum toughness requirement is to ensure that the pipe used in “accessories” has reasonable resistance to fracture initiation rather than propagation. Regardless of propagation, you definitely don’t want to use brittle pipe anywhere.

      • Chris Hughes says:

        Agreed, and that has more to do with transition temperature than absolute toughness – and certainly the 27J minimum is not relevant, particularly as the ‘pipeline assemblies’ have a design factor of 0.67 or less (usually considerably less since Schedule wall thicknesses are used.

      • Simon says:

        Its a tricky situation in terms of demonstrating code compliance. I absolutely agree with Chris that given the short and generally flanged nature of the pig traps we shouldn’t be designing for running fracture. That leaves fracture initiation. We are generally using a design factor of 0.6 for assemblies and accessories.
        AS 2885 does not differentiate between pipe as part of an assembly (pig traps are an assembly as opposed to an accessory) and line pipe. This means you never get to apply the likes of AS4041 or B31.3 that wouldn’t require minimum toughness to be demonstrated. Therefore in most cases i can remember we have always specified the likes of API 5L PSL 2 pipe or even ASTM A333 Gr. 6.
        Its not a bad idea demonstrating a minimum toughness but it can make the 6m of pipe needed for the whole job problematic to procure.

  4. Chris Hughes says:

    I wonder whether the committee which wrote the latest revision of Part 1 ever actually considered the difference between pipe used for pipeline assemblies and the main linepipe? After all we are really only talking about the major barrel and the kicker line, as the minor barrel is usually made from the heavy wall linepipe for which ductile fracture control has already been specified.

    Without having fully read and absorbed the changes in the 2012 revision, I would be inclined to use good engineering judgement in this matter, rather than slavish Code compliance: as long as the result is Approved then there should be no problem.

    • petertuft says:

      Clause 1.6.2 of Part 0 is always available if you have a good justification for deviating from black-letter compliance with the code and can get your design approved by the Licensee. There has been some off-line discussion about piping with low stress levels (<85 MPa and <40% SMYS) which is not vulnerable to either brittle or tearing fracture. So if specifying toughness testing for such pipe becomes unreasonably onerous Clause 1.6.2 might be the get-out-of-jail card. But you need to be very careful and very confident when you call on that.

      • Simon says:

        Just noted AS2885.1-2012 Clause deals with fracture control of assemblies. Not quite definative but enough to discuss an interpretation that fracture control of the pig trap assembly (including the major barrel) can be assessed to a plant piping code like ASME B31.3

  5. David Benjamin says:

    I find a little ambiguous in relation to the requirements for meeting the 27J for seam welds.
    Per final sentence in says Test methods for fracture toughness shall be in accordance with Appendix K.

    Appendix K only calls out taking samples form the pipe body per Figure K1. Hence if the samples are only proving that the pipe body is >27J then is it applicable to seam welds.
    Is the requirement therefore governed by Fracture initiation resistance in (b) read in conjunction with 4.8.2 (b) (C) and 4.8.2 (d).

    If the fracture initiation toughness only needs 14J does the seam need to be >27J? As the requirements of API 5L (section 5.9.3) is not specifically called out in AS2885 then what governs seam weld toughness?

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s