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Failures of concrete pump delivery pipeline end fittings and hoses

Issued: 15/04/2021
Last Updated: 20/04/2021

Purpose

This  safety alert highlights the risk of failure of concrete pump delivery lines including  failures of end fittings.

Businesses  that fit end fittings to concrete delivery hoses and pipes should follow and  document sound engineering practices and provide information on inspection  methods to customers.

Concrete  pump owners should obtain information from suppliers of pipes and hoses on the  manufacturing methods used and appropriate inspection methods.

Background

There have been incidents in Queensland where delivery lines  have failed and sprayed concrete under pressure.

Failures included a:

  • rubber  delivery hose failure
  • coupling  stem cracking with the end breaking away (refer Photograph 1)
  • end  fitting starting to separate from the rubber hose (refer Photograph 2) with the  concrete spraying out of the gap
  • flange  cracking and breaking away from a steel 90-degree, 6-inch to 5-inch reducer  bend, located at the hopper (refer Photographs 3 and 4).

Concrete  pumping pressure can be in excess of 85 bar, especially when blockages occur. All  of these incidents had the potential for serious injuries if workers had been near  to where the failure occurred. In one incident, a car’s windscreen was broken  approximately 15 metres away.

Photograph 1 - Cracked and failed part of a hose stem.

Photograph 1: Cracked and failed part of a hose stem.

Photograph 2: Swaged end fitting that has separated from the hose.

Photograph 2: Swaged end fitting that has separated from the hose.

Photograph 3 - Failed flange on steel reducer bend.

Photograph 3: Failed flange on steel reducer bend.

Photograph 4 - Location of steel reducer bend.

Photograph 4: Location of steel reducer bend.

Contributing factors

Hoses and end fittings can  fail due to:

  • the  pressure rating of the concrete pump exceeding that of the rubber hose or end  fittings
  • incorrect  tolerances on the inner and outer parts of the coupling
  • the  swaging or crimping procedure does not comply with the manufacturer’s  specifications
  • incorrect  specifications for the rubber hose
  • excessive  wear—especially on the internal part of the fitting from concrete flow.

Flanges on steel pipes can  fail due to:

  • poor  welding due to incorrect electrodes, incorrect preparation, lack of  penetration, or other welding irregularities
  • flanges  and pipes being made from steel types that can be difficult to weld
  • poor  matching of flanges to pipes (i.e. the flange doesn’t fit well on the pipe end)
  • mishandling  of the pipe flange (i.e. bashing the flange or pipe with a hammer when the  adjacent pipe and/or hose clamp isn’t aligned)
  • poorly  fitting hose clamps (e.g. incorrect size, concrete build up).

Action required

Concrete pump owners

Concrete pump owners need to ensure that the pressure rating  of the concrete pump does not exceed that of the pipeline. For example, if a  pump is rated at 85 Bar concrete pressure then it is unacceptable for steel  pipeline to be replaced with rubber hose with a maximum rating of 45 Bar. Owners  must also take reasonable steps to ensure that a quality assurance program is followed  while attaching the end fittings so that failure of the end fittings is avoided.  It is generally easier to obtain certification from a local supplier when  purchasing equipment.

If a concrete pump owner imports components from overseas, it  may be more difficult to obtain trustworthy information on the manufacturing  process. This is the case when the overseas supplier is unknown or there is no  manufacturer's mark. Unscrupulous manufacturers have also been known to copy  manufacturers' names and trademarks, so marking of products alone may not  provide adequate evidence that the product is fit for purpose.

A concrete pump owner who imports equipment from overseas  takes on the duties of an importer under the Work Health and Safety Act 2011 (WHS Act). The importer must carry out, or arrange to have carried out, any  calculations, analysis, testing, or examination of the equipment to control safety  risks.

Suppliers of pipes and hoses

Suppliers of hoses and pipes with end fittings should ensure  a quality assurance program is followed while attaching the end fittings and  that information on this program is available for the purchaser.

Suppliers should also provide documented instructions on the  operating parameters of the product along with inspection methods to be used.

If the supplier attaches end fittings to pipes or hoses, the  supplier takes on the duties for manufacturers under the WHS Act in addition to  those duties for suppliers.

Fitting end fittings to hoses

End fittings are attached  to rubber hoses using two methods, crimping and swaging. With the  crimping method, compressive forces are  applied radially to the outside part (ferrule) of the end fitting with the  inner stem inserted inside the end of the hose. A crimped end fitting can be  clearly recognised by obvious indentations on the outside of the end fitting  (refer Photograph 5). With the swaging method, the end fitting is attached to  the hose when the end fitting is pushed onto the end of the hose under  hydraulic pressure. Although there will be some marking on the end fitting from  the manufacturing process, swaged end fittings do not have obvious indentations  like a crimped end fitting. Photograph 2 is an example of a swaged end fitting  that is partly separated from the hose.

Although crimping and  swaging are fundamentally different, both methods rely heavily on using quality  components of the correct tolerances along with ensuring a stringent process  for attaching the end fittings is followed.

Hose manufacturers will typically  only certify that their hose is capable of withstanding specified concrete  pressures when high quality hose ends are fitted. Some hose manufacturers operate  under the concept of a matched pair where they will only guarantee their  hose for a maximum pressure, when end fittings from a particular manufacturer using  a verifiable crimping or swaging method are used.

Photograph 5 - Crimped end fitting clearly showing crimping indentations.

Photograph 5 – Crimped end fitting clearly showing crimping indentations.

When assembling end  fittings on hoses ensure:

  • compliance  with all of the conditions specified by the hose and/or end fitting  manufacturer
  • the  hose material and dimensions are suitable for concrete pumping and for fitting  of the specific type of end fitting
  • the  size of the external and internal parts of the fitting must be within the  tolerances specified by the hose manufacturer or fitting manufacturer for the  dimensions of the hose used
  • the  method of attaching the end fitting must comply with the specifications of the  manufacturer (information from the hose manufacturer may also be needed).

Testing of the end fitting is one way to help  demonstrate the integrity of the connection. Proof testing of all fittings or destructive  testing of samples are methods that can be used. If proof testing is carried  out, the test method needs to ensure the fitting and hose are not damaged.

Following attachment of the end fitting to the hose,  the fitting should be permanently marked with information on the batch number  and an identification mark of the company attaching the end fitting. This will assist  with traceability and authentication of the assembly procedure. The method of  marking must not adversely affect the integrity of the hose assembly.

If there is any  doubt about the manufacturing criteria or testing relating to the end fitting,  the advice of the original equipment manufacturer (OEM) should be obtained. If  this is unavailable, the advice of a suitably qualified professional engineer should  be obtained.

Documented  information on the method of attaching the end fitting should be maintained by  the business attaching the end fitting and should be available on request.

Welding flanges to steel pipe

Welding flanges  to steel piping used for concrete pumping is a complex issue and requires high  levels of technical input and skill to ensure the welding process will result  in a quality product.

The following  should be ensured:

  • Only  pipe specifically intended for concrete pumping should be used. Prior to  welding, there should be some reliable method of verifying that the pipe and flanges  are the actual type ordered.
  • The  weld specifications are to be compatible for the pipe and flange material  characteristics and pressure specifications of the pipe being welded.  Information should be obtained from the pipe manufacturer on this issue.
  • Welding  should be in accordance with a detailed weld procedure that includes electrode  selection, pre-heating instructions (where required) and the use of a welding method  that is recommended by the pipe manufacturer.
  • Carrying  out destructive testing on a test sample to verify the welding method is fit  for purpose.

Inspection of hoses and pipes

Owners and  operators of concrete pumping equipment need to ensure ongoing inspection of pipes  and hoses is carried out. Inspection methods and intervals for measuring pipe  thickness are outlined in the Concrete Pumping Code of Practice 2019 (PDF, 1.97 MB). However, in addition, an inspection  program should be applied to end fittings on rubber hoses and flanges on steel  pipes.

Inspection of hoses

Documented information  on inspection of hoses (i.e. from the OEM), should be provided by the business who  fits the end fitting and this should be passed on by the hose supplier to the  end user.

The inspection  program should include an inspection before use and a periodical inspection  with the interval based on the frequency of use and the operating environment.

The inspection program should  include:

  • an internal inspection with sufficient  light levels checking hose tubes are of reasonable thickness, there is no  textile fabric or steel reinforcing exposed, there are no blockages, rips, cuts  or tears of the liner tube, and there are no collapsed sections of the inner  tube or hose
  • an external inspection checking for cover  damage including cuts, tears, abrasion exposing the reinforcing material, chemical  attack, kinks or collapsed areas, soft spots, cracking or weathering
  • inspection of end fittings for  excessive wear and thinning of the wall thickness
  • visual  inspection of end fittings for cracks. If there’s any doubt or there is a  history of cracking, non-destructive examination may be required
  • checking end fittings are intact and  not slipping from the hose due to old age or from mechanical pulling loads.

Inspecting welded flanges on steel pipe

In addition to  thickness testing of steel pipeline (specified in the Code of practice) and  checking the pipeline for damage, it is important to check flanges on concrete  pumping pipe.

The inspection program should  include inspection of:

  • welds  for cracks, missing weld, weld undercut and weld consistency
  • flanges  to check they are not deformed and do not have hammer marks
  • pipe  ends internally for uneven wear and cracking
  • flanges  to ensure they are free from concrete build-up and other foreign material.

Further information