Valve safety is boosted
15 Jan 2000
Offshore safety is compromised by the low usage of coded key interlocking systems in process valve applications. Many operators prefer the low cost and simplicity of a padlock and chain to, what they perceive as, a complicated key interlocking unit.
Sigma has introduced the Prosafe MTV 3, which combines the simplicity of padlock systems with the enhanced safety of coded key interlocks. The system, claims Sigma, overcomes many objections associated with previous key interlock systems and is a contribution to increased safety.
The importance of fail-safe interlocking in offshore safety procedures was highlighted in the Cullen report following the Piper Alpha disaster. In his report Lord Cullen said: 'A physical locking off system should be an integral part of PTW procedures because of the security it provides against inadvertent unauthorised de-isolation.'
The report continues: 'all permit to work systems should incorporate a mechanical isolation procedure which involves, wherever practicable, the physical locking off and tagging of isolation valves to prevent their accidental or unauthorised opening...'
The MTV3 is a handwheel operated 'one size fits all' interlocking device which prevents unauthorised or accidental mis-operation of gate and globe valves up to 14in diameter, and gear operated valves of virtually any size. An even simpler design has also been developed for lever operated ball and butterfly valves.
With the MTV3 fitted, a valve may be locked closed and/or open, and may be operated only when the correctly coded key is inserted and trapped. It has a patented self setting and adjusting counting mechanism which automatically adjusts to suit valves within any number of turns up to 500 revolutions. An automatic self setting mechanism is activated the first time the lock is operated
Auto Slack Adjustment allows the MTV3 to overcome the problem experienced with many existing designs, where worn seals and/or gearbox backlash cause the fully closed position of a valve seat to change over time.
