Posted on 29 January 2016

The Emerging Use of Digital Technologies to Support Mechanical Interlocking Valve Processes

Single Point Control

Eni Norge, part of the globally operating ENI group,  is an energy company in oil & gas production and one of the major operators on the Norwegian continental shelf. To enhance safety and protect its operators, Eni Norge looked to simplify its valve processes by moving the control and operation of its large number of valves to a single, safe location. Eni Norge approached us to solve the problem and this led to the development of the custom-built operating panel.

The electronic operating panel aggregates all single valve control points away from the local site into one graphical system. The panel works as a communication and verification system and enables an operator to control a sequence of actuated valves directly from the panel. Although the operating panel can be used in a wide variety of applications, in this case the panel was specifically designed for use with a pigging procedure, and two panels were installed on an FPSO built for use in the Goliat Field, the first oilfield to be developed in the Barents Sea. Each panel controlled four valves.

Designed around the requirement to isolate power to the panel, the operating panel incorporated two interlocked key units to ensure a specific sequence of operation:

  • The operator selects to close the valves as required
  • Red LED lights verify that the valves have reached their fully closed position
  • When all valves are closed, the operator can isolate the panel by removing the ‘A’ Key
  • The ‘A’ key is then entered into the solenoid key unit and only when the safety and automation system also confirms all valves are closed, a permissive signal is sent to energise the solenoid and release the ‘B’ key
  • This allows the operator to safely continue the mechanical interlocking sequence and, in this instance, only after the panel has been isolated and all the valves have been closed and locked, will the final key be available to manually unlock the pig trap door to load or unload a pig.

Valve Operating Panel

Two-Tier Safety System

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.

Risk factors that contribute to pipeline pigging incidents include a lack of operator training or complacency, a lack of hazard awareness or workers relying solely on pressure gauges creating a false sense of security.

Interlocks ensure extremely high levels of safety by guaranteeing that valve operation sequence occur in the correct, safe order. However, they usually function as stand-alone safety systems. A serious incident during a pipeline pigging process highlights the importance of moving towards the integration of digital technology into traditional safety systems for a two-tier safety system.

Two workers were attempting to remove a pig from a line launched the previous day but found the pig stuck in the reducer section of the pipe. It had passed the main block valve so the valve could be closed but remain wedged in the entrance. The workers depressurised the pig receiver in standard, safe working practice and opened the vessel door to the atmosphere. It was assumed that the energy has been removed. However, when the workers attempted to remove the pig by attaching a length of stainless steel tubing, the pig shot out and struck one worker on the nose, resulting in major facial injuries. On review, it was found that the pig had created a temporary seal with a weld in the reducer section and created a pressure trap behind the pig. Once the operator attempted to manually move the pig, the pressure blasted the pig out of the receiver at high speed.

During such a pigging operation certain safety conditions need to be met: as the example above shows, 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 guaranteed that all required valve operations were performed as outlined, but the accident still occurred. The process industry’s preventative actions outline that along with risk assessment and hazard identification and the proper training of personnel, there must be procedures in place to address both the normal and upset conditions on the ground.

This has led to the development of SmartTrap+, which combines digital technologies with traditional interlocking. SmartTrap+ incorporates signals from other field devices like pressure or H2S/CO2 sensors into the interlocking sequence, and only releases keys for mechanical interlocking if all conditions in the process have been met. It offers the highest level of process safety by offering proof.

SmartTrap for Pig Trap Interlocking

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 pressure signals and SmartTrap+ into the interlocking sequence, interlock keys can only be released if the pressure in the pigging system has been equalised. This would mean that SmartTrap+ would detect pressure build up in the pig receiver and refuse access to  vessel closure door; the key to the vessel door will only be released when the pressure inside the vessel is acceptable and no dangerous gases or residue are detected. SmartTrap+ provides electronic confirmation of sensors across the process; it reduces the need for operators to climb up and down ladders across the site to manually confirm all signals and reduces the scope for operator error.

SmartTrap+ has taken the single-point control concept a step further by delivering real-time information into the process. SmartTrap+ can work in conjunction with the operating panel to offer full, safe control over dangerous processes.

Real-time Management

The implementation of RFID (radio-frequency identification) technology is an increasing trend in the oil & gas industry. RFID tagging gives the ability for real-time monitoring of processes as tagging pipeline components can register faults and deliver maintenance history to keep processes moving. RFID technology allows the track and trace of products and this has been utilised by operating companies to ensure safe interlocking sequences.

Using a key management system with RFID provides an enhanced level of system security for mechanical interlocking keys. Statoil, the largest oil and gas operator on the Norwegian continental shelf, includes a requirement for electronic key cabinets in its governing document that covers the technical requirements for valve position securing systems for safeguarding and maintenance. It states that an electronic key cabinet system will include key panels and key tag readers, electronic ID tags and system software. It is important that such a system is ‘future-proofed’, allowing for the expansion of systems without overhauling the current installation.

A huge benefit in using RFID in this way promotes operator accountability and improves worker performance. For example, with SFC’s SmartKey+ management system, all keys are trapped in the cabinet and only authorised personnel are able to gain access to the keys appropriate to them. This system again reduces the burden from the worker at the local site. Keys can be tracked in real time, providing the operator and control room personnel with information on interlocked processes and their statuses; a full transaction history is available. This can ease maintenance work by providing a reviewable process of key activity and frequency of use. It also uses license-free software that enables systems to be expanded without significant expense. Also, the ability to retrofit RFID tags into existing key systems already in use means that safety systems can be quickly brought up to date.

SmartKey+ Key Management

The user is identified by a unique access code and once authorised, selects and removes the appropriate ‘initiating’ key from the panel as the selected key position is indicated and unlocked. The worker can then use this key to start the mechanically interlocked process in the pre-defined sequence. Once completed, the user scans the key in front of the scanner and returns it to the appropriate, highlighted section.


Operating companies have recognised that the integration of digital technology with mechanical interlocking provides multiple benefits.

Firstly, the safety of the operator is paramount, and integrating digital technology reduces the burden from the operator at the local site. It enhances safety by providing umbrella control over dangerous and complex processes. This extra layer supports the traditional use of mechanical interlocking by providing communication and proof of ongoing valve operations.

In addition, complex processes often benefit from incorporating digital technologies by boosting efficiency. The single-point control can streamline a process that often includes multiple valves and hazardous manoeuvres. Workers can feel supported by the two-tier safety system and, as in the case of SmartTrap+, no longer need to seek out manual confirmation of sensors and signals around an interlocked process, which can lead to human error.

RFID technology offers real-time monitoring of key movements during dangerous valve processes. It leads to improved inspection and maintenance by offering reviewable data that reduces downtime and associated costs. This has the knock on effect of increasing worker accountability and improving operator performance.

The emergence of electronic technology is the natural progression of the industry. It works to support the traditional method of interlocking valve operations and together they enhance safety and streamline processes, a win-win.

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