Failures of concrete pump fittings and hoses.

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.

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.