Innovative safety solution for valve change-over
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Smith Flow Control product story
Edited by the Engineeringtalk editorial team
Apr 20, 2000
Process safety specialist Smith Flow Control has designed an innovative interlocking system for the change-over sequence between relief valves.
Process safety specialist Smith Flow Control has designed an innovative interlocking system for the change-over sequence between relief valves at Norsk Hydro's Rafnes Petrochemical Refinery in southern Norway.
At the refinery, the change-over of relief valves for the cooling water system is achieved using handwheel-operated 3-way diverter globe valves, which divert the process flow from one relief valve to another.
Under these conditions, partial valve operation to its mid-position must be strictly controlled.
Previously, the two diverter valves were linked by a chain wheel operator, which meant that operation of one valve caused simultaneous operation of the other.
The drawback of this system, however, was that it was liable to failure if the chain on the wheel slipped or broke.
The consequences of such a failure were potentially very serious and could have resulted in fugitive emissions or even an explosion.
In this closed system - with diverter valves located both upstream and downstream of the relief valves - it was decided to install a safety interlocking system which would ensure the downstream valve was always operated first.
Following a site inspection, Smith Flow Control engineers devised a process which utilised a custom-designed hybrid GLM/QLA interlock on the downstream valve and a standard GLM interlock on the upstream valve.
The system works as follows: a key is issued from the permit control authority to initiate the sequence.
When inserted into the GLM unit of the hybrid interlock on the downstream valve, it allows the valve to be operated, but only to a mid-position.
This releases a second key from the QLA unit, which is used to unlock the GLM interlock on the upstream valve, allowing its full operation.
This in turn releases a third key, which is returned to the QLA unit of the downstream valve, enabling further operation to complete the changeover.
This fool-proof system ensures a safe operating mode at all times and eliminates any scope for operator error.
Manufactured from 316 stainless steel, Smith Flow Control interlocks are certified to the highest international standards and can withstand the most arduous conditions, both on and offshore.
Depending on the process or required level of sophistication, they can be customised with switches, sensors or microchips to interface with stand-alone or mainframe process management systems.
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