Background
Under regulation 6.33 of Mines Safety and Inspection Regulations 1995 (MSIR), pressure vessels are required to be designed to Australian Standard AS 1210 Pressure vessels. This includes designing for all possible loading, as stated in section 3.2.3 of AS 1210, which includes horizontal forces such as wind, earthquake and external pipe loads.
To remain stable pressure vessel supports require resistance to uplift and sliding. It is unlikely that connecting pipework would have been designed to act as restraining members under these circumstances, unless it has been clearly stated on a design drawing.
The stability of pressure vessels also relies on a supporting structure which is designed by a competent person, applying the referenced standards in section 3.24.2 of AS 1210.
Inspectors have observed that the anchorage and vessel support information on some pressure vessel drawings is inadequate. There were also numerous instances where the support conditions for pressure vessels were not satisfactory.
Supports were observed:
- not anchored securely (no hold-down bolts)
- not anchored to a structural member
- with significant loss of material due to corrosion.
Some of these vessels had previously been inspected by a classified plant inspector. These inspections, recorded in the classified plant record book, noted no defects.
Potential defects of support condition cannot be remedied unless it is noted or recognised. Correct defect identification and subsequent remedial works will ensure conformity with the design intent and the ongoing integrity of the pressure vessels.
Summary of hazard
If pressure vessels are not anchored, or have inadequate support, horizontal forces can tip them over or cause uncontrolled movement. This can overstress the nozzle connections, pull flanges apart or result in other unexpected responses from the vessel, exposing personnel around the vessel to an increased risk of harm.
Contributory factors
- Support information is not documented in the pressure vessel design drawings.
- Poor condition of supports is not identified as a potential defect or hazard.
- Inspection personnel may not appreciate the scope of their responsibilities as required by the applicable Australian Standards.