12 June 2012

Don't use valves with brazed-in nozzles on ammonia systems, says IoR

UK: THE Institute of Refrigeration has recommended that valves, where the valve nozzles are brazed into the main body, should not be used on ammonia refrigeration plant.
This latest safety alert comes as an update to a guidance note issued in May last year. It follows an incident in 2010 when a refrigeration engineer received severe burns from an unexpected ammonia release at a food distribution warehouse.

While the original guidance note blamed the incident on corrosion, further recent failures of this type of valve suggest that this is not the only cause. The IoR reports that the assembly of the valve is susceptible to lack of complete fusion of the brazing filler ring, which in turn weakens the joint of the side port to the valve body.

'The Institute of Refrigeration recommends that all such valves, where the valve nozzles are brazed into the main body, should not be used on ammonia refrigeration plant,' says the update.

It further says that any valves fitted to existing systems should be carefully examined. If there is any doubt as to their integrity they should be replaced immediately with a suitable valve manufactured with a one-piece body, and should be treated with extreme care until they are replaced.

'This should include clearly labelling the valve with a warning, protecting it from accidental mechanical impact and using appropriate PPE when working on the system in the vicinity of the valve,' it concludes.

In the original incident at a distribution warehouse in 2010, the refrigeration engineer received severe burn injuries when a significant amount of refrigerant was suddenly released while he was in the process of removing a valve cap from a DN 15 (½') charging valve. The valve was installed on the low pressure side of an ammonia system.

The engineer was using a check spanner to hold the body of the valve whilst undoing the cap with another spanner but even so the valve connection to the plant failed.

It was concluded that the failure was due to corrosion under the preformed brazing filler metal thus weakening the joint on to the valve parent metal. The corrosion had started externally and that forces exerted in fitting the valves, removing caps or fitting charging lines etc, may have damaged the valve.

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