Combining Mechanical Interlocks with Process Safety Sensors
In the process industry, mechanical interlocks guarantee strict adherence to procedures and help avoid human error. They are particularly useful for highly dangerous operations such as pigging and valve changeover procedures.
While interlocks ensure extremely high safety levels, they usually function as stand-alone safety systems. New digital technologies are now emerging that enable traditional nterlocking to be combined with digital process control and instrumentation systems.
Smith Flow Control is the first company to combine these mutually beneficial technologies in the development of the SmartTrap+, which incorporates signals from sensors into the interlocking sequence.
During a pigging operation certain safety conditions need to be met: the vessel pressure should be at a safe level and all dangerous gases and residue must be removed before opening the pig door. Mechanical interlocking guarantees that all required valve operations are performed, but cannot guarantee the outcomes of these operations.
For example, opening and closing a vent valve does not give real time information that the vessel pressure has actually reached a safe level; while opening and closing a drain valve does not guarantee that all residue has been removed.
By incorporating signals from other field devices like pressure or H2S/CO2 sensors into the interlocking sequence, the SmartTrap+ ensures interlock keys can only be released if particular process conditions have been met. So, for example, this could mean that the key for opening the vessel closure door will only be released when the pressure inside the vessel is acceptable and no dangerous gases or residue are detected.
SmartTrap+ incorporates permissive signals and a door lock proximity switch (4- 20mA) as standard. The signals can include (but are not limited to) pressure detection, gas detection, flow/ level and pig detection.
Some of the factors contributing to pipeline pigging incidents include:
• Lack of training or complacency
• Lack of hazard awareness
• False sense of security and reliance only on pressure gauges
• SmartTrap+ effectively deals with these factors, making pigging a safer operation and grants full traceability in real time.
The process industry's standard preventive actions include:
• Hazard identification and risk assessment including management of changes
• Awareness, training and competencies of personnel
• Procedures that address normal and upset conditions
SmartTrap+ reinforces these actions and implements genuine physical control on any pigging operation.
For operators needing to ensure higher levels of process safety, the SmartTrap+ is an ideal solution. By incorporating the best of traditional mechanical interlocking with process sensor information to ensure all vessels are safe to access, it will help to reduce accidents and reduce downtime.
Smith Flow Control Ltd
Tel: 01376 517901
Published in Valve User Magazine Issue 33
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