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.
