Venting pits, and the value of

There was a recent query about the requirements of AS 2885.1 for venting below-ground structures such as valve pits. It turns out the Standard is incomplete, because an editorial change in 1997 inadvertently omitted a key sentence and no-one noticed until 25 years later. Subsequent revisions of the Standard had applied the “ain’t broke, don’t fix it” principle and failed to notice the broken bit.

On the one hand the fact that no-one noticed could be interpreted as meaning that the relevant clause is in fact not very relevant at all. On the other hand, just because a requirement is not referred to very often doesn’t mean the Standard should ignore it. If and when you are designing a large below-ground pipeline structure the sealing or ventilation of it could be critically important to safety. In any case, others have possibly noticed the anomaly but had no easy way of raising the issue to get it fixed. provides an avenue for any user of the Standard to raise issues such as this.

So what was the problem? Clause 6.5.3 of AS 2885.1-2018 specifies that below-ground structures of less than 6 m3 volume may be sealed or vented, but is silent on larger structures. It turns out that AS 2885-1987 (note the year!) included a sentence that “Any other structure shall be ventilated.” (i.e. must not be sealed). However that sentence was lost from all subsequent revisions. More detail here.

The take-home message is that no matter how hard committees try to get AS 2885 exactly right there are things that slip through, but if you find anything that you think is incomplete, wrong, ambiguous, etc then send an email to And if you have to design a big pit, make sure it is ventilated in accordance with Part 1 Clause 6.5.2(d).

Pigging a lined pipe – response (and a record-keeping caution)

The previous post gathered a number of helpful responses from experienced industry people. But before getting to the technical responses there is an interesting sub-text to this topic, relevant to everyone in the pipeline industry. None of the following is intended to be critical of the current operator, quite the contrary – they have recognised a problem from the past and are working to resolve it.

It seems likely that somewhere in the 30 year history of this pipeline there has been a loss of important documentation (i.e. details of the lining, appropriate procedures for pigging). Like many pipelines it may have been through several ownership/management changes over its life and would not be the only pipeline to have lost records.

I once came across a pipeline for which the new owner’s bean-counters had decided not to incur the storage cost for any documents older than 7 years (the tax office rule). But the as-built documentation was older than that …

Of course the importance of keeping construction and maintenance documentation should be blindingly obvious, until it isn’t and something like this happens.

To the technical nitty-gritty about pigging a lined pipe:

  • There was a general consensus that wire brush pigging a lined pipe is not a good idea (no surprise there).
  • Lining damage may be indicated by epoxy flakes or dust found in debris from past pig runs, if there are relevant records or access to people who were involved at the time.
  • Whether lining damage matters depends on the purpose of the lining, which we don’t know. Lining is most commonly provided to reduce friction factor (increase flow and/or reduce pump/compressor cost). A flow lining which has been badly scratched is probably ineffective.
  • Flow analysis may permit back-calculation of friction factor and hence internal roughness of the pipe; there would be a lot of subtleties in the analysis, it would have to use transient flow modelling (unless the flow is perfectly steady), and may or may not be sufficiently precise to reach a clear conclusion.
  • Finally (and pedantically) to be strictly correct the lining is most unlikely to be FBE (Fusion Bonded Epoxy) – almost certainly liquid-applied epoxy.

On the basis of available information, we can’t say whether or not the existing lining has been damaged, but if the original reasons for lining the pipeline are still relevant and additional pigging runs are now needed, then the use of nylon brushes seems justified.

Pigging a lined pipeline

A question has been submitted to which is outside the experience of the team, so we thought we see if someone else out there is able to help:

A transmission pipeline was previously wire-brush pigged on a few occasions in the last 30 years. However the current operator has recently realised that the line has FBE internal lining.

The question:  Is there any value in using a nylon brush pig for future pig runs? Or is the lining likely to be already so damaged that further wire brushing doesn’t matter?

What is external interference?

There has been discussion in some of the AS 2885 committees about exactly what “external interference” includes. It is probably fair to say that the meaning of “external interference” seemed so clear and obvious to those involved in drafting the various revisions of Parts 1 and 6, over many years, that it never occurred to us that an explicit definition would be needed. That now looks like an oversight as some misunderstanding has developed.

The nearest thing we have to a definition is unfortunately buried in Clause C6.1 of Appendix C to Part 6:

The nature of external interference involves the removal or penetration of the protective ground cover and contact with the pipe.

Even that is not quite complete because it leaves unstated that external interference is a result of human activity and does not include natural events. So external interference is intended to cover only those threats that involve direct impact to the pipe during excavation (including digging, boring or any other ground-penetrating activity).

This is not new, and in fact has been a fundamental aspect of the safety management process ever since the concept of risk assessment was introduced in the 1997 revision of Part 1 (i.e. 24 years ago!). The whole SMS process is based on two broad categories of threat:

  • External interference
  • Everything else (corrosion, natural events, design or construction shortcomings, operational shortcomings, etc)

There are two reasons for this distinction:

  • Damage by direct impact to the pipe during excavation has long been known to be the overwhelmingly dominant cause of pipeline incidents and failures
  • Very specific design and operational measures can be specified by AS 2885 to mitigate such threats

From Part 1 Clause 5.4.1:

The purpose of physical controls is to prevent failure resulting from an identified external interference event by either physically preventing contact with the pipe or by providing adequate resistance to penetration in the pipe itself.

The purpose of procedural controls is to minimise the likelihood of external interference activity, with potential to damage a pipeline, occurring without the knowledge of the pipeline operator, and to maximise the likelihood of people undertaking such activity being aware of of both the presence of the pipeline and the possible consequences of damaging it.

Clause 5.4.4 and Tables 5.4.4(A) and (B) then go on to specify that physical protection measures must include both separation and resistance to penetration (with multiple subcategories), and that procedural protection must include both pipeline awareness and external interference detection (again with multiple subcategories)

All these requirements (and the further much more detailed requirements) are focussed specifically on protection against excavation activities, and make little or no sense for other types of threat.

So it is simply not correct to classify as “external interference” threats such as:

  • external loads due to vehicles (no contact with pipe or possibility of penetration)
  • ground movement (not human-caused, no possibility of penetration although severe deformation may cause rupture)
  • exposure of the pipe due to erosion (ditto)
  • anything else to which the principles of physical and procedure protection against human-caused impact and penetration don’t make sense

Above-ground pipes may look like a grey area, since removal of ground cover is obviously not applicable. However the other principles of protection by separation and penetration resistance are still relevant, as are procedural measures. So the external interference rules are still relevant to threats such as vehicle impact on aboveground pipe.

Everyone involved in pipeline safety management studies should be aware of what constitutes external interference, whether the SMS is for design or operational purposes.

Barred tee fabrication

We’ve been quiet lately, for a whole lot of reasons largely related to being a volunteer team. But there has been a recent update to with guidance on how to fabricate a barred tee without welding in the area of the extrusion neck. It’s the second item on this page and also copied below.

It is interesting that this method was normal practice at least 40 years ago, but sometimes old knowledge can be lost if it is not documented somewhere such as in a Standard as has now been done.

Barred tees: What is the reason behind the addition of Clause 5.6.2(e) in AS 2885.2-2016 (Clause 5.6.2(d) in 2020 version), which states that “pig bars shall not be welded directly to the high stress areas around the extrusion neck”?

On any forged fitting it is recommended to only weld at the weld preparation area, as stresses caused by welding can cause cracking at subsurface features such as laminations. This is often not detected using Magnetic Particle Inspection unless it is surface breaking. The passage of the pig could then cause failure of the bars and a stuck pig scenario.

The diagram below is a guide (not definitive) showing how the pig bars are welded to the pup piece rather than the extruded neck.

AS 2885 supporting documents

We have added to some links to potentially important background information, with the relevant page copied verbatim below. The documents were originally published over 10 years ago and became unavailable for a while but remain important.

This is not exactly bedtime reading. In fact parts of it can be quite dense and difficult to digest. But sometimes if you are grappling with the interpretation of AS 2885, or trying to understand why it says what it does, you might find this useful. In fact, you might as well download the two documents right now and file them somewhere handy.

In preparing each revision of AS 2885 the committees have often prepared Issue Papers that discuss a topic in detail and conclude with recommended changes to the Standard. These are working papers that tend to be abandoned when sufficient work has been done to reach a recommendation, even though the document may in some ways be incomplete or unpolished. For this reason most are not suitable for publication. However for the revision of Part 1 in 2007 nearly 80 Issue Papers were prepared and later edited for publication in 2010.

Since 2010 all Parts of AS 2885 have been revised, in some cases very substantially. However each revision of a Standard tends to build on the work of the previous revision. Hence much of the 2010 background documents remains valid as an explanation and justification for current content of Part 1 and to some extent Part 6 (which was split out from Part 1 in 2018). Users who refer to these documents must form their own judgement about the applicability to the current revision of the Standard. Note that the clause numbers referred to in the Issue Papers are for AS 2885.1-2007 and will be different for the 2018 Standards.

This Issue Paper publication project resulted in two large PDF documents:

  • “The APIA Guide to AS 2885”, August 2010
  • Appendix 2 to the Guide, “Issue Papers Prepared as Basis for AS 2885.1, Revision 2007”

APGA members can download them from the APGA Knowledgebase. Due to idiosyncrasies in the Knowledgebase metadata they are best found by searching for the date on which they were added to the Knowledgebase: 12/07/2021.

Some pages in this wiki refer to specific Issue Papers from the 2010 suite.

Over 60 Issue Papers were prepared prior to the 2018 revisions of Parts 1 and 6 but remain in their incomplete and unpolished state. The intellectual property of these papers lies with APGA. They may or may not be made publicly available in future. Requests for background information or copies of particular Issue Papers will be considered and may be granted depending on circumstances.