What can augers do?

(I still intend to complete the series of posts on ALARP by making suggestions about estimating likelihood, but one or two other things first.)

Almost any safety management study needs to consider the threat of pipe damage by augers, either vertical (for power poles etc) or horizontal (bores and HDDs).  I’ve run numerous workshops where there has been little argument against the suggestion that while an auger might penetrate a pipe it is highly unlikely to result in rupture.  This is because penetration will take place slowly (unlike an excavator or ripper impact) and once high pressure gas (or oil) emerges the rig operator will stop drilling rather than continue until the hole exceeds the critical defect length (resulting in rupture).  We usually assume a maximum hole size equivalent to a 30-50 mm orifice.

Penetration by an auger seems to be a very unlikely event anyway.  Unless the auger hits the pipe square on or is in extremely hard ground it will almost certainly veer off and skid around the side of the pipe, possibly causing horrible gouging but not penetrating.  It also assumes that the operator would persevere (perversely?) after hitting a hard obstacle, notwithstanding the allegedly distinctive noise of auger on metal.

But then there are events like this:

Ruptured pipe and pole

Ruptured pipe and pole

Drill rig

Drill rig

The fire dying down

The fire dying down

That’s near Cleburne in Texas on 7 June this year.  It didn’t get extensive media coverage because “only” one person was killed.

The damage was caused by a very large auger preparing to erect very large concrete poles.  The man in the first picture gives a sense of the scale.  (Incidentally, that first picture also shows a lovely fracture propagation and arrest.)  But although the auger was large, so was the pipe.  I don’t have enough details to work out the critical defect length, but it’s a fair guess that it would be a lot bigger than the pilot bit of the auger.

So I’m interested to hear other views on the potential for augers to cause serious damage to pipelines.  Do you think my hand-waving arguments above are valid?  But what about the Cleburne incident?

(I’d like to develop a research proposal for the Energy Pipelines CRC to look seriously at the scope for augers to damage pipelines, but even if I get that together and it’s approved it will be quite some time before results are available.  Anyone interested in working with me on that?)

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15 Responses to What can augers do?

  1. Colin Symonds says:

    Peter,
    By the looks of it the Cleburne drilling rig is more than you standard pole auger – this type has drill guides so it is unlikey to slip off the pipe and has a lot of grunt – I suspect in addition to this the critical defect length was shorter than the diameter of the pilot – but that is only speculation – also unknown to us is the material spec, wall thickness and condition of the pipe.
    With regard to the operator smelling the escaping hydrocarbon fluid this would be expected to be almost immediate for vertical bored holes but ceratinly not so for horizontal bores partiuclarly when drilling mud is being employed.

    • petertuft says:

      Interesting point about drilling mud restricting release of pipeline fluid. I can only speculate, but suspect that while the mud might delay the appearance of gas or oil at the borehole entrance the delay would only be slight if the pipeline is operating at typical transmission pressures (a few MPa or higher). I’m guessing that would push the mud out pretty quickly.

      I just don’t know about the small HDD rigs that are used for installing minor services in suburban streets. Do they use drilling mud? Mud could be quite difficult to handle in an urban street environment, especially since they bore at shallow depth and hence have high risk of frac-out.

      These rigs are a worry because any small to medium contractor can buy one for little jobs. I’ve heard rumour that the NBN fibre optic cables are being installed along suburban streets using small HDDs, and if that’s generally true it will mean many thousands of km of boring through suburbia, guaranteeing quite a few hits on all sorts of things! (One hopes mostly not transmission-pressure pipelines.)

  2. Liz Brierley says:

    Peter,
    SEA Gas would be interested in getting involved in a EPCRC project that looks at potential damage from augers. We are in the process of carrying out a survey of landowners, contractors and utilities etc. to update our knowledge of the equipment being used around the pipeline. We then intend to look at carrying out some field tests using SEA Gas pipe.
    Liz

  3. Adrian Amey says:

    Peter
    Not sure if you remember the 2002 EGP incident at Wetherill Park in Sydney’s west. An auger drilling a hole for a concrete pier to support a road way hit the Horsley Park to Smithfiled section of the pipeline top dead centre putting a 50mm dia hole in the pipe.

    It did not “slip off” and just drilled straight through the pipe. Fortunatly the operator stopped the rig immedialty and shut it off with the auger bit still in the hole.

    There was no ignition and no rupture but it took a few hours to blow down all the gas. One other interesting fact the pipe was over 10 metres deep so “cover” was not an effective protection measure in this case.

    Adrian

    • petertuft says:

      I remember it well. There were a number of unique conditions, and it seemed to be such an unusual circumstance that it isn’t something one would need to consider in most safety management studies. In fact it illustrates my point about the auger slipping off UNLESS it is well guided by the ground conditions (10 m depth of 1 m diameter hole is not going to go sideways very easily).

      I also agree that cover usually is no protection against augers, and sometimes wall thickness isn’t either, which makes it rather difficult to comply with the AS 2885 requirement for two physical protection in urban areas.

      All of which reinforces the need for some investigation of this threat.

      • Chris Hughes says:

        I totally agree that, when dealing with drilling equipment (and HDD equipment is likely to be an even greater threat than augers) it is impossible to comply with the one or two physical protection measures requirement. Perhaps the amendment of AS2885.1 which is being prepared for issue in 2011 should recognise this.

  4. Chris Hughes says:

    With regard to Colin’s response, the majority of transmission pipelines do not contain odourised gas and so the auger operator is likely to notice the sound and visual effects of the gas leak rather than the smell.

    At SMS workshops that I facilitate I always ensure a difference is noted between a “pendulum” type auger (the sort that hangs off the back of a tractor for digging fence post holes) and a guided auger as shown in the Texas photos and frequently used for power pole installation, water well drilling, etc. The third type which needs to be considered is the core drill used for mineral exploration – since these cut a circle rather than having a pilot point they are more likely to create a large (critical?) defect before the gas release is detected and the machinery stopped.

  5. Chris Hughes says:

    When assessing the threat of puncture by any sort of drilling equipment I always make the point that there is no form of physical protection that can be guaranteed to give 100% mitigation from the threat (with the possible exception of depth of cover against a pendulum auger installing fence posts) and so any drilling threat has to proceed to an assessment of frequency/severity.

    When carrying out such an assessment it may be worth looking at it twice: once for gas release without ignition and once for gas release with ignition. This is because the European statistics indicate that the frequency of gas release with ignition is at least an order of magnitude less than that of gas release without ignition, and this is likely to affect the frequency assessment of the threat on the AS2885 matrix: the severity of an ignited gas release is always going to be greater than that of an unignited release.

    The point is well made that in many (if not most) cases the operator of the drilling equipment is likely to notice that he has hit an unexpected object before he has reached the point of penetration: our assessment has to assume that despite this he continues to drill until penetration is achieved. We are however allowed to take the probability of him continuing to penetration into account when assessing the frquency of the event.

  6. Geoff Callar says:

    Peter
    APA will obviously have a big interest in this.

    Jemena might still have some abandoned pipe that you could ‘borrow’, which was previously used for some of Phil Venton’s impact tests.

  7. Pingback: More on augers | Pipelines OZ

  8. Stephen Dykes says:

    I am not a good blogger but yesterday was asked to comment on the Smithfield incident – as Operations Manager at the time for Duke I can confirm the following:

    The pipe in the HDD section was DN200, 5L X65, 9.1mm line pipe.

    The auger was drilling at a depth of approximately 10m when the auger pilot tip (approximately 1 inch in diameter) penetrated the pipeline that was operating with a gas pressure of approximately 3900kPa. The hole was top dead centre – you could not be more accurate. The auger operator immediately shut down the plant when he heard the hiss and then smelt the gas.

    some comments……

    There was no ignition at the source because of water down the hole. Most drilling operations use water/mud.
    The leak rate was less than what would flow out of a 1 inch hole at 3900 KPa because the auger machine pilot drill was not pulled out of the hole so the pilot drill remained blocking the hole in the pipe restricting the flow. Once the pipeline was blown down the auger was extricated and there was a clean 1 inch hole bang on centreline of the pipe.
    Ignition could occur at the surface if spark available (smoking, exhaust) but did not occur in this incident
    Restricted flow if ignited unlikely to cause fatality but could result in burns
    Unlikely to be an explosion because initial air in the hole displaced by boring equipment and then gas release results in rapid acceleration of air/gas mix beyond explosive limit
    Unlikely that the operator will continue drilling because of the sound and smell of gas.
    Probably a good thing to provide induction to all auger/boring/drilling plant operators to immediately shut down plant if safe to do so and NOT move drill head at all and get out of there up wind and report.
    Don’t allow augers anywhere near the pipeline!!!!
    Make sure that as-builts are accurate
    If you must allow an auger near the pipeline, always have a pilot drill on the auger but restrict the size of the pilot drill. Certainly do not want to cause damage to the pipe that is greater than the critical defect length. This is almost certainly what happened in the Texas pipeline rupture case Peter has included photos of – look at the design of the auger and the fracture nature of the resultant full bore rupture..
    There are various arguments about augers deviating away from pipe – Murphy says NO – it will hit centreline and not deviate at all… I do agree that this is totally dependent upon auger assembly design.
    The only controls you have are procedural and ultimately the fracture toughness and penetration resistance of the pipe. For most drilling gear, the penetration resistance is useless as the tip of the pilot drill is designed to penetrate!!!!
    If the drill diameter is less than critical defect length and it penetrates you will have a leak and a restricted leak if the drill is not removed.
    If it is greater than critical defect length then Boom, Boom, Boom.

    • Adrian Amey says:

      Hi Steve
      Two more items to the list of things to do.
      1 – When using a pipe locator do a sanity check on the outcome if overhead power lines cross the pipe nearby.
      2 – Dont belive marker signs.
      Adrian Amey

      • petertuft says:

        Relying on pipe detectors or marker signs is too uncertain. Before any excavation very near a pipeline the pipeline operator should use tangible means of locating the pipe – potholing, vacuum excavation, water lancing, etc. Of course, that might be relaxed if the proposed excavation is only in the general vicinity of the pipe rather than right next to it. I guess each licensee has their own rules for this sort of thing.

      • Adrian Amey says:

        Peter

        Agree totally. Have a couple of digital photos of the event which show it but couldn’t load them.

        Adrian

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