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

29 January 2016

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.

Pipeline Safety and Security – the Role of Key Interlocks

18 August 2015


Pipeline operations in the oil and gas industry are safe if carried out correctly but can have catastrophic consequences if performed incorrectly, particularly if high temperature, high pressure or toxic/flammable product is present.

The industry generally has a disciplined approach to pipeline design and operating practice, governed by recognized international standards and enforced by regulators and certification authorities. While good practice begins with good design, both are inevitably hostage to the ‘human factor,’ which is responsible for 70 percent of all reported incidents and accounts for 90 percent of financial loss.

Human Factors Engineering (HFE) is the design of work processes and systems to ensure the safe and efficient functioning of workers by taking into account human capabilities, limitations and requirements.

Pipeline valve systems must be designed for safety rather than placing sole responsibility on the operator. Distractions, misunderstandings, shift changes or simple accidents can all lead the operator to make catastrophic errors. Simply relying on operator adherence is not enough – safety must be applied to the process itself. The focus then becomes accident prevention, not accident management.

Mechanical Interlocks

Mechanical interlocks remove the ‘human factor’ by ensuring dangerous processes happen only in a designated sequence. They are simple mechanical locks designed as integral-fit attachments to the host equipment such as valves and pig traps – any equipment needing human intervention. Workers transfer specific keys from lock to lock (equipment to equipment) in a particular sequence. Each step in the process is only possible after the previous step has been completed and the sequence must be followed in the exact order to completion.

An interlock is essentially a dual key device that locks the host process equipment in one or more conditions. The standard condition is with one key trapped in the interlock and the valve is locked in status ‘1’ with the second key elsewhere. To operate the valve to status ‘2’ the second key is obtained from a control room and inserted into the interlock. The valve is then operated to status ‘2’, releasing the initial key and trapping the second one. The released key can then be used to operate the next valve in the sequence or returned to the control room if this is the end of the sequence.

When not in use the initiating key for each system should be kept in a locked key cabinet in a control room, with visual status indication at all times.

Mechanical interlocks are ideally suited to integrate with permit-to-work procedures. The Cullen Report on the Public Inquiry into the Piper Alpha Disaster (1990) strongly recommended the use of locking systems integrated with permit-to-work procedures, especially where routine procedures cannot be accomplished in the time-scale of a single work shift. They ensure safety, rather than place responsibility on the operator. Well-designed key interlock systems are always operator-friendly – they require no additional effort than normal procedures would require and, most importantly, should never permit more than one key to be free (available) at any one time.

Primary and Secondary Safety Systems

Whether a pipeline or process module is of simple design, with basic functions controlled by manually-operated valves, or of complex design controlled by sophisticated mainframe Distributed Logic Control (DLC) systems; key interlocks can provide a totally reliable mechanical assurance of safe operating practice in which the operator’s scope for error is eliminated.

Within DLC controlled systems, which invariably incorporate electrical interlocking (‘trips’), these are usually limited to governing only the operation of high-criticality motorized valves. Associated miscellaneous services valves (e.g. for venting) may be manually-operated valves and will therefore not be recognized by the DLC management system. Correct operation of these valves may still be critical or semi-critical and may be dependent solely on the operator following written operating instructions.

In DLC-managed systems, key interlocks can form a vital link between managed and unmanaged valves. In these circumstances, the key interlocks are not intended as the primary safety system but as a secondary back-up system to the primary (DLC) system. Designs have been developed in recent years to provide key interlocks that offer the only total form of interdependent control over the operation of motorized and manually operated valves in one fully integrated system. When applied to motorized valves, the interlock design ensures that the failsafe function of the valve is never compromised.

In process systems where the valving and/or control components are all manually-operated (i.e. not DLC controlled), key interlocks become the primary safety system. They are particularly suitable as the primary safety system for remote locations where power is unavailable.

Typical Specifications for Valve Interlocks

Valve interlocks should be used in the following situations:

  • Where it’s possible to isolate a relief valve by means of a block valve
  • Where it’s possible to isolate the flare system
  • To ensure that a pig launcher or receiver is properly depressurized, vented and drained before the closure is opened and that no line valve can be opened when the closure is open
  • For process reasons

All interlocks should adhere to the following:

  • They must be suitable for use in external, industrial environments that also may be a corrosive, tropical, desert or marine location
  • They must be durable, robust and easy to operate with gloves
  • They should be 316 stainless steel for strength and corrosion resistance
  • The internal mechanism should be free from galling and lubricated for life
  • All key entry points should contain a device to prevent the ingress of dirt and water
  • They must be fitted to the valve manufacturer’s standard supply valve without any alteration to the valve except to remove or modify the valve handwheel or lever
  • They should be suitable for installing on an inline valve
  • All special tools for installing, commissioning or adjustment of interlocks should be supplied with the interlocks, along with simple graphical installation instructions
  • They should be maintenance-free and tamperproof
  • The interlock body must be stamped with the appropriate tag number and tagged with the applicable key codes and reference letter
  • As the interlock replaces the original valve operating lever or handwheel, it should be supplied with the nearest available lever or handwheel size to suit the interlock
  • They must be coded to provide the operating sequences specified in the material


  • Operating keys should have a colored key tag bearing the system tag number and the key code reference
  • The key should be 316 grade stainless steel or better
  • It should be impossible for an interlock to be inadvertently operated by a key not coded for use with that interlock
  • The key shall be easy to use even with gloves.
  • With the exception of the system initiating key, which is held in the control room key cabinet, all other system operating keys will be trapped in their respective interlocks
  • At the owner’s discretion, spare or duplicate keys can be provided. These should have strikingly different colored key tags to any other keys on site

Key Cabinet

  • The control room initiating key cabinet should be lockable and fitted with a synthetic glass window to allow easy visual assessment of the status of all of the interlock systems
  • Each interlock system should have its own dedicated position, bearing the system tag number and revealing “Work in Progress” when the key is removed
  • The color of the cabinet tags should contrast with those of the key tags
  • Key cabinets should be made from mild steel suitable for a protected indoor environment
  • If spare or master keys are required they should be housed in separate, lockable key cabinets with solid doors and contrasting cabinet tags

Smart Key Cabinets 

Pigging operations are particularly dangerous, as opening a pig trap closure while there is pressure in the barrel can shoot the pig out of the launcher at high speeds. Attempting to pass a pig through a partially open outlet valve, or prematurely opening the pig trap in the presence of high levels of toxic hydrogen sulfide, can cause fatal consequences. There are a few simple steps to launch a pig safely using key interlocks. Each step traps and releases a key and can only be performed in a particular order. To begin with, keys are used to unlock and open the vent and drain valve respectively. These actions release a key that can then be used to open the vessel door safely and load the pig. Once the pig is loaded and the vessel door is closed and locked, a key is released to close the drain and vent. This action releases the key that opens the kicker valve and launches the pig. Once the pig is launched, the trap is re-isolated by closing and locking the mainline valve. This releases a sequence of keys that depressurize the trap by closing the kicker and opening the vent and drain. The final steps involve closing all valves; the final key is returned to the control room key cabinet where is it kept until the process starts again. No steps can be by-passed in this sequence, nor can steps be taken out of order. This simple, failsafe process ensures accidents cannot happen.


The global trend of contracting out site operations inevitably translates into the ‘casualization’ of labor, which in turn leads to an increased risk of accidents through human error or deliberate violations.

Well-designed interlocking systems can mitigate these risks – either by eliminating error or by greatly inhibiting the potential for violations. They should always be operator-friendly,require no additional work effort from the operator than normal procedures would require and, most importantly, should never permit more than one key to be free at any one time. The message is, ‘keep it simple.’

A common sense approach to valve safety

7 August 2014

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Working on location in the oil and gas industry is a stressful environment. Workers operating valves are exposed to constant noise and activity and undertake dangerous, repetitive tasks that often require intensive labour. Contractual staffing arrangements combined with hazardous working conditions can result in physical injury and an increased risk of accidents and loss of product. A significant 70% of accidents in the oil and gas industry are attributed to the ‘human factor’. Human Factors Engineering (HFE) is the design of work processes and systems to ensure the safe and efficient functioning of human beings, by taking into account human capabilities, limitations and requirements.

System safety

In the oil and gas industry, valve systems must be designed for safety, rather than placing sole responsibility on the operator. Distractions, misunderstandings, shift changeovers or simple blunders can all lead the operator to make catastrophic errors. Simply relying on operator adherence is not enough in such a dangerous, fast paced environment. Safety must be applied to the process itself. The focus then becomes accident prevention, not accident management. work systems provide a way of controlling potentially dangerous tasks. They outline necessary steps, such as maintenance procedures, that require isolating particular machinery. Padlocks or chains work procedures require clarity, accurate identification of hazards, thorough checking, and adherence by operators. This process places responsibility on the employee without system support.

In contrast, using mechanical interlocks removes the ‘human factor’ by ensuring dangerous processes happen only in a designated sequence. Interlocks are relatively simple, specialised, mechanical fit attachments to the host equipment. These interlocks are attached to the host equipment (any valve, closures, equipment needing human intervention) and compose of a simple lock and key design. Workers transfer specific keys from lock to lock (equipment to equipment) in a particular sequence. The next step in the process is only allowed once the previous step has been completed. The sequence must be followed  in the exact order to completion. Mechanical interlocks are ideally suited to integrate with work procedures. Indeed, the Cullen Report on scale of a single work shift. They ensure safety, rather than place responsibility on the operator.

For example, mechanical interlocks are a suitable safety system in the operation of pig traps. Pigging operations are inherently dangerous and written safety procedures are not enough to ensure operator safety. Opening a pig trap closure while there is pressure in the barrel can shoot the pig out of the launcher at high speeds. Attempting to pass a pig through a partially open outlet valve, or prematurely opening the pig trap in the presence of high levels of toxic H2S, can have fatal consequences. Using a sequence of interlocks on the pig trap vessel ensures an operator can only unlock and open the vessel door to retrieve the pig after the vent has been opened. This makes sure that the system is depressurised and protects the operator from exposure to dangerous H2S or the pig shooting out of the vessel.

mechanical interlocks fitted to pig trap door

Figure 1. This is an example of a mechanical interlock on a vessel closure, such as one used in pig traps. The door is locked but when the key on the right is inserted, the locking arm is released, allowing the door to open. 


Mechanical interlocks make  sense from a productivity standpoint too. Interlocks can ensure the safe transfer of product. For example, Smith Flow Control’s (SFC) valve interlocking system was installed on a Malaysian LNG installation at Bintulu in Sarawak,  East Malaysia, to prevent accidental product spillage while tankers are loading. By integrating a safety system into the process it eliminated the risk of human error or negligence when loading the tanker, which could lead to a vessel leaving the transfer area, still connected to the onshore facilities via a loading arm. This would result in damage to equipment, product spillage and a potential fire hazard to plant and personnel.

The LNG installation at Bintulu is one of the largest LNG facilities in the world; the loading site features hydraulically actuated loading arms, which are manoeuvred into place from a control station. Once connected, the supply valve is opened up allowing product transfer to the tanker. Two interlock units were integrated into the system; one in the control station and a small valve lock was fitted to, the hydraulic supply line on the LNG supply valve. Only a single key is used between the two units. When the single, interlock key is in place in the control station switch panel lock, the hydraulic loading arm can be manoeuvred into place. Once the arm is connected to the ship, the key is released from the lock and used to unlock and open the valve in the supply valve actuator. The supply valve can now be opened in the usual way, allowing safe and efficient product transfer. While the transfer takes place, the key remains trapped in the valve lock, preventing operation of the loading arm. Once transfer is complete, the supply valve is closed, enabling release of the key, which is then returned to the control station, reinstating controls of the loading arm and allowing it to be retracted. Using Smith Flow Control’s interlocks, the system can only operate in this defined sequence. Well‑designed key interlock systems are always operator‑friendly – they require no additional work effort from the operator than normal procedures would require – and, most importantly, should never permit more than one key to be free (available) at any one time.

Malaysian LNG












Figure 3. This is an example of an LNG facility, discussed in the case study example (Malaysian LNG installation).

Valve operation

Principles of HFE can be applied to the physical operation of valves onsite. An increase in the diversity of the workforce age, gender, and physical strength requires consideration. Operating valves can expose operators to risk of musculoskeletal injury through repetitive twisting and stretching. Valves can vary in size and can require over a hundred turns using excessive, sustained force by several operators at once. Using a portable valve operating system can reduce the stress on workers and improve productivity.

Figure 2. A portable valve actuator.

portable valve actuator - EasiDrive

SFC supplied a number of portable, pneumatic valve actuators called EasiDrive to energy and chemical company Sasol in South Africa to ease operation and improve efficiencies. Prior to EasiDrive, manual operation of valves at Sasol created safety concerns. Worker fatigue meant that not all the valves were opened or closed fully, resulting in potential safety hazards. Emergency shut off valves were not operated as efficiently as expected, again causing safety issues. Operators needed to carry out more frequent maintenance and servicing on the valves to ensure that operation effort was kept as low as possible which, in turn, reduced productivity. The new valve actuators at Sasol eliminated these concerns.

Valve operating systems can offer reduced operation time and fewer health problems for personnel. They offer improved emergency response through fast operation and status feedback of critical valves. In addition, they are ideal where severe weather conditions can make operations more challenging.

Occasionally, valves may be located in dangerous or inaccessible areas and require permanent access. However, unavoidable constraints on accessibility mean that operators have difficulty ensuring valves in critical service are properly open or closed. Remote valve operating systems are the common sense approach to these valves, ensuring that operators are kept at a safe distance while valves are actuated efficiently. Remote valve operators, such as FlexiDrive, can pass through walls and floors and operate valves via a drive cable at distances up to 30 m. It allows workers to stay in safe designated areas while critical valves are operated remotely.


Many routine procedures are potentially dangerous if executed incorrectly or in unsafe conditions, with the scope for injury and/or damage significantly increased when high temperature, high pressure or toxic/flammable product is present. By taking simple steps to integrate safety into valve operating systems, workers are protected and work processes flow in a designated, safe way. Interlocks are versatile building blocks that can be configured to meet almost any simple or complex procedure. And drive systems are cost‑effective ways to operate difficult to open and/or hard to reach valves, protecting personnel while increasing efficiency.