The processing and transportation of oil and gas presents many safety challenges. While pipelines are the most viable means of transport over long distances, measures are always necessary to eliminate any possibility of error – either accidental or through deliberate sabotage.
The oil and gas industries generally have a disciplined approach to pipeline design and operating practice, governed by interna¬tional standards and enforced by regulators and cer¬tification authorities. While good practice begins with good design, both are inevitably hostage to the ‘human factor’. It is estimated that up to 70% of reported incidents in the oil and gas industry worldwide are attributable to human error and account for in excess of 90% of the financial loss to the industry.
The contracting out of key functions inevitably increases the risk of accidents through human error. Reliance on written safety procedures is an act of faith in the alertness and goodwill of the worker. Accident prevention and violation reduction requires physical systems that compel compliance.
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. Mechanical interlocks play a role in HFE by adding an additional safety element to the process.
Mechanical key interlocks
Key interlock systems are single or dual-keyed mechanical locking devices which operate on a ‘key transfer’ principle, controlling the sequence in which process equipment is operated. Interlocks are now widely accepted as an effective safety management tool and used by every major operating company across the world to adhere to HFE.
Typically they 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. handwheel or push-button) enabling operation of the valve or switch.
The interlocking process starts with the use of an initiating key, which unlocks the equipment. When the operation is complete, a secondary (previously trapped) key may then be released, locking the equipment in the new position. This secondary key will be coded to operate the next interlock in the sequence, and so on. Using this extremely simple coded-key transfer principle, a ‘mechanical logic’ system is created which minimises the risk of operator error and ensures safe plant operation.
Mechanical key interlock systems are ideally suited for integration with Permit-to-Work (PtW) procedures; indeed, the Cullen Report on the public inquiry into the Piper Alpha offshore rig disaster (1990) strongly recommends the use of locking systems integrated with PtW procedures, especially where routine procedures cannot be accomplished in the time-scale of a single work shift.
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.
Much of the world’s hydrocarbon reserves are situated in or under some of the most inhospitable regions, including deserts, the Arctic, tropical jungles and oceans. Finding, accessing and extracting these reserves takes a monumental effort and is a multi-trillion dollar industry.
Ensuring the safety of plant and personnel in these conditions can be a real challenge for operators. Extreme weather or physical conditions not only contribute to the wear and tear of pipelines and process equipment – they also make the maintenance and operation of valves and interlocks much more challenging.
Working in extremely hot, humid or cold environments each presents its own challenges, but they can all make the work tiring and stressful. In the Persian Gulf, for example, where temperatures can reach 50°C, workers are exposed to constant heat while undertaking dangerous, repetitive tasks that often require intensive labour. In extreme cold environments such as Prudhoe Bay in Alaska, where temperatures can reach the opposite extreme of -50°C, the challenges are different but just as demanding. Workers may need to wear bulky clothing and gloves, for example, making the operation of equipment more difficult. Contractual staffing arrangements in most projects, combined with hazardous working conditions, can also result in an increased risk of accidents.
In these and other extreme environments, valve systems must be designed for safety rather than placing sole responsibility on the operator. Simple blunders can lead the operator to make catastrophic errors, so simply relying on operator adherence is not enough – safety must be built into the process itself. The focus then becomes accident prevention, not accident management.
The principles of HFE can easily be applied to the physical operation of valves in extreme environments. Some valves can require over a hundred turns using excessive, sustained force by several operators at once. Under these circumstances, portable valve actuators can reduce the stress on workers and improve productivity, especially with valves that require a high number of turns or are otherwise difficult to operate because of high torque. With the tool, one operator can efficiently work banks of valves, dramatically reducing fatigue and the risk of injury.
Valves may also be located in dangerous or inaccessible areas but still require permanent access. In these circumstances operators may have difficulty ensuring valves 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 operating systems can pass through walls and floors and operate valves at some distance away. In this way they allow workers to stay in safe, designated areas while critical valves are operated remotely.
Case Study – Ichthys LNG Project, Australia
The Ichthys LNG Project, currently under construction 220 kilometres off the coast of Western Australia, is one of the most significant oil and gas projects in the world, involving some of the largest offshore facilities in the industry, a state-of-the-art onshore processing facility and an 889 km pipeline uniting them. The project’s onshore processing facility is located in Darwin, the capital of Australia’s Northern Territory, where daytime temperatures rarely fall below 30°C, with high humidity.
The project owners place great emphasis on the safety and wellbeing of its operators, adhering to best practice HFE principles to ensure quality, safety and fit for purpose equipment and facilities. HFE includes all those considerations that enhance or improve human performance in the workplace and minimise the possibility of human error. Consideration is given to all work processes and systems, ensuring the safe and efficient functioning of workers by taking into account human capabilities, limitations and requirements.
Smith Flow Control’s interlocks are used throughout the facility to provide protection for over-pressurisation of vessels and other valves across the plant. A twin or multiple relief system enables a relief valve to be removed for service without the need to shut-down the system. Interlocks guarantee an open path to pressure relief is maintained at all times during maintenance or other work exercises on process equipment, removing the possibility of both or all relief valves being simultaneously isolated. A simple mechanical valve interlock system ensures that no relief valve can be isolated until the spare relief valve has been brought on-stream. A spare relief capacity enables continuous production while maintenance procedures take place, eliminating the need to isolate and shut down the whole process, maintaining efficiencies at all times. In total, over 2,500 interlocks were supplied to the Ichthys onshore processing facilities.
As an additional layer of safety, interlocks were specified on the facility’s main pig trap, serving the main line from offshore. The vessel closure interlock was fitted to a 42” pig trap receiver, connecting to the large subsea pipeline.
Pig traps are launching and receiving stations that allow operators to insert and remove pigs (pipeline tools) without interruption to the pipeline product flow. The greatest danger occurs when opening the pig launcher or receiver door; during this part of the process, the launcher/receiver vessel can be under pressure if there is nothing to prove its status. Opening the vessel without correctly isolating, venting and draining can cause the trap door to fly open and the pig to shoot out at high speed, with potentially fatal consequences. Key interlocks negate this risk by mechanically proving the ‘closed and isolated’ status that enables venting and draining of pig trap vessels before loading or unloading operations.
Over 1,000 of Smith Flow Control’s EasiDrive portable valve actuators were also supplied to the Ichthys project to help ease valve operating problems.
Many routine pipeline operations are potentially dangerous if executed incorrectly or in unsafe conditions and this is exacerbated in extreme environments. By taking simple steps to integrate safety into valve operating systems, workers are protected and operations proceed in a designated, safe way. Interlocks are versatile building blocks that can be configured to meet almost any simple or complex procedure. In addition, portable or remote valve drive systems are cost-effective ways to operate difficult to open and/or hard to reach valves, protecting personnel while increasing efficiency.
For more information, contact Ms. Louise Cracknell at +44 (0) 1376 517901, Email: firstname.lastname@example.org, or email@example.com ; or visit www.smithflowcontrol.com
About Smith Flow Control
Smith Flow Control Ltd is a British company specialising in mechanical valve control equipment. This includes procedural control using mechanical valve Interlocks and activity management systems, EasiDrive portable valve actuators, and FlexiDrive mechanical valve linkage systems for remote and/or simultaneous valve operation.