Valve Safety and Mechanical Valve Interlocking
Introduction
It is essential that the processing industries take a disciplined approach to design and operating practice. Valve operating procedures can be potentially dangerous if executed incorrectly or in unsafe conditions. The scope for injury and/or damage is also significantly increased when high temperature, high pressure or a toxic/flammable product is present. While good practice begins with good design – both are inevitably hostage to the ‘human factor’. 70% of reported incidents in the oil and gas industry worldwide are attributable to human error, accounting for in excess of 90% of the financial loss to the industry.
SFC mechanical valve interlocks
Modern processes are often highly automated yet still require human intervention during essential maintenance procedures such as loading or unloading pig traps or the changeover of pressure relief valves. Distributed control systems (DCS) cannot effectively regulate such procedures, but mechanical key interlocking system can.
Smith Flow Control is responsible for introducing the coded-card linear-key concept in a range of modular key-operated interlocks which regulate operator execution of work procedures on any form of host process equipment. These can be used on every form of valve (including motorised and instrument valves) as well as access hatches/doors and electrical isolating switchgear.
What are key interlocks?
Mechanical key interlocks work by controlling the sequence of events in which valve process activities are conducted.
Key interlocks are dual-keyed mechanical locking devices designed as integral-fit attachments to the host equipment and operate on a ‘key transfer’ principle. This limits actions to only those that produce a safe and desired outcome – for example preventing a tanker from departing a loading/discharge station until the cargo hoses have been disconnected.
Typically key interlock systems are applied to valves, closures, switches or any form of equipment which is operated by human intervention. The ‘OPEN’ or ‘CLOSED’ status of an interlocked valve, or the ‘ON’ or ‘OFF’ status of an interlocked switch, can only be changed by inserting a unique coded key. Inserting the key unlocks the operating mechanism (e.g. hand wheel or push-button) enabling operation of the valve or switch. Operating the unlocked equipment immediately traps the initial (i.e. inserted) key.
When this operation is complete, a secondary (previously trapped) key may be released, thereby locking the equipment in the new position. This secondary key will be coded in common with the next lock (item of equipment) in the sequence. By this simple coded-key transfer principle, a ‘mechanical logic’ system is created which denies the scope for operator error.
In addition, keys may be customized to intelligent format by electronic tagging of individual keys and managed by system software that interfaces with the mainframe DCS system.
While popular Permit to Work (PtW), Lockout/Tagout procedures provide a ‘lock-off’ capability, they do not provide any control of the sequence of operations, nor do they assure or confirm the status of the equipment to which they are fixed which can generate dangerous conditions through error or negligence. Interlocks are ideally suited for integration with PtW procedures and provide an effective front-line safety management tool that mitigates the risk of human error.
For more information please contact:
Mr Lakshmanan Venkateswaran
Smith Flow Control Sales Manager for India
Halma Trading and Services India Pvt. Ltd.
201 Hyde Park, Saki Vihar Road
Powai, Mumbai, Maharashtra, 400 072
Tel: 022 4200 0700; Fax: 022 6708 0415
E-mail : V.Lakshmanan@smithflowcontrol.com
Website : www.smithflowcontrol.com
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