Clamp bolts used to connect the pipe work had failed for no apparent reason after recent pipe installation work, according to the Construction, Forestry, Mining & Energy Union (Mining & Energy Division).
A safety alert issued by the Union said the tensile overload type fracture of the clamp bolt occurred at a change of section approximately 10mm from the underside of the bolt head.
“The fracture was considered to have occurred as a result of hydrogen embrittlement from the pickling process prior to galvanising,” the alert said.
“The root cause of the hydrogen embrittlement was attributed to the bolt having a hardness level that complied with the requirements of property class 12.9 bolts rather than the specified property class 8.8 bolts.
“Property class 8.8 bolts (as specified) are suitable for galvanizing and are not susceptible to hydrogen embrittlement from the pickling process. Delayed fracture of the bolt after installation/tensioning was also indicative of hydrogen embrittlement.
“Further to the investigation the mine have sent away a selection of bolts from different types of clamps utilised on site and the problem was found to exist with only the Minquip type clamps.”
Industry Safety and Health Representative
District Union Inspector
Construction, Forestry, Mining & Energy Union (Mining & Energy Division)