Safety relief valve failure: autoclaves boiler-pressure system

The purpose of the safety relief valve is to open automatically at a predetermined pressure to prevent equipment failure and for the protection of persons. They are fitted as a backup safety measure to hot water pressure systems.

In a recent incident, an autoclave's boiler electrical contact failed, causing the temperature of the boiler to increase uncontrollably. The safety relief valve, which failed to open, was designed to release at an operating pressure of 630 kPa. The boiler was found to be operating off the scale of the gauge - indicating an operating pressure in excess of 900 kPa.

In addition, several pressure relief valves have failed their inspection due to seizure of the manual pressure release lever not being operable and therefore non-operative in an automatic capacity (as a safety device) to release pressure when required.

Boiler and pressure vessels are inspected annually, but should be maintained throughout the year as per the manufacturer's recommendations, and all records of maintenance recorded in the vessel's logbook or on MAXIMO.

The brass safety relief valves, the type that failed, require more frequent maintenance than the stainless steel insert variety. Both types/models of pressure relief valves require ongoing routine maintenance. However, the stainless steel valve as quoted in the manufacturer's recommended service advice, indicates less frequent maintenance is required, and with increased resistance to corrosion, they are less prone to suffer from seizer. The lifespan of the stainless steel valve is also longer.

When a pressure relief valve needs replacing, it is advisable to consider the quality and maintenance issues.

Budget Unit management are reminded to ensure that they comply with all of the manufacturer's recommendations in regard to the maintenance and operational use of safety relief valves on boilers and pressure vessels under their control.

Potential gas leak from poorly seating gas regulators on cylinders

There are apparently some older style inert gas cylinders still around campus (and the region) being circulated. These inert gas cylinders (eg argon) have a MULLER cylinder value (see photo below), with a 11 mm star shaped hole. A large leak may develop because the regulator 'o'-ring fails to cover the hole, thus allowing gas to escape around the thread.

BOC gases is aware of the problem (poor design), and all such cylinders were supposed to have been withdrawn from service.

All gas cylinders fitted with a MULLER value (with large star shaped hole) should be returned to the supplier.

Use of these gas cylinders may lead to an asphyxiation hazard, and rapid consumption of gas.

Moving gas cylinders safely

The recent introduction of new valves to many inert gas cylinders has highlighted the importance of moving the gas cylinders in a safe way. The new valves, which are in line with the Australian Standard (AS2473), have the outlet to the side, and valve wheel/handle on top.

There have been several reports of 'near misses' [1] associated with the plastic dust plug being fired out of the outlet under pressure if the user inadvertently moves the cylinder by holding the valve handle. Of particular concern are 'G' sized cylinders, as these outlets are around eye level of many users, with the potential for blindness or brain damage.

Part of this problem is poor handling practice, and design. To minimise the risks, the correct handling technique is outlined below.

Handling a gas cylinder correctly over short distances

(eg moving a cylinder on or off a trolley or into a gas cage or manifold) Note: large gas cylinders (like the 'G' size) are heavy. If you are not comfortable controlling this weight, ask for assistance. Lifting a gas cylinder should not be attempted.

Gas cylinders must always be moved without a regulator or gas fixture.

a) Always wear good footwear, like safety boots, to prevent foot injuries.

b) Always wear leather gloves, like riggers gloves - this will give you better grip, prevent cuts to the hand, or discomfort due to hot or cold cylinders.

c) Ensure you have space to move the cylinder safely, being able to control its movement without sustaining awkward postures or risk tripping/falling over.

d) Firmly grip the cylinder neck (the space between the cylinder body and the valve, not the valve handle) with your thumb and fingers in a 'C' fashion. This is your support hand.

e) Position your feet shoulder width apart and with one foot behind the other, for greater stability.

f) Tilt the cylinder slightly (2-5°) towards you. Keep your support hand close to your body while moving the cylinder.

g) With your free hand, rotate the gas cylinder.  It should move easily in the direction you want it to go.

h) Position the cylinder in its desired location.

i) Return the cylinder to an upright position, maintaining a firm grip on the cylinder to prevent it toppling over.

j) Ensure the gas cylinder is securely restrained.

Handling a gas cylinder correctly over distances

Use a gas cylinder trolley.

a) Correspondence within Commonwealth OHS Officers, December 2004.

b) ANU Hazard Alert. Gas cylinder valve change for Air and Nitrogen compressed gases (2004)

Note: this issue also relates to other gas suppliers conforming to the Australian Standards and members of the Australian and New Zealand Industrial Gas Association (ANZIGA).

For further information email: OHS Officer