Stringent Anti-Surge Valve specifications can pose challenges for larger valves on LNG liquefaction trains. But Severn’s bespoke Anti-Surge Control Valves ensure efficiency and compliance, delivering high‑performance surge protection for LNG, petrochemical and industrial gas compression systems.
LNG compressor manufactures are placing increasingly stringent performance requirements on Anti-Surge valves, and specifications are often written without considering valve size. Yet while the standards are easily achievable for smaller valves, they become significantly more difficult as valve travel (the distance the plug moves) increases. Since specifications are primarily based on safety and efficiency requirements, any deviations introduce risk; concessions are not generally accepted.
Looking for Anti‑Surge Valve expertise?
Technical challenges for large Anti-Surge Valves
Fundamental principles of physics make it harder for larger valves to achieve the optimised, highly efficient control required in Anti-Surge applications. The weight of the valve plug and the long linear stroke of the actuator introduce mechanical inertia and lag, which can result in a slower or more erratic valve response. Consequently, to ensure safety, end users have traditionally had to tolerate a conservative approach to surge control when using larger valves. This compromises overall system efficiency.
Severn’s Anti-Surge Control Valves are engineered to overcome these challenges, and we recently put a 30” test specimen through its paces with dynamic testing. Results prove that even large valves commonly found on LNG mega trains can fully comply with rigorous compressor manufacturer specifications. This demonstrates our capability in designing large‑diameter anti‑surge valves for severe‑service applications, LNG mega‑train operations, and high‑capacity centrifugal compressors.
Dynamic testing for Anti-Surge Valve
Dynamic testing for Anti-Surge valves determines how a valve performs when subjected to operational parameters that will be encountered on the liquefaction train. Speed, precision and stability are the critical features evaluated, especially for mission‑critical surge prevention applications in LNG and gas processing plants.
Assessing speed of response
Anti-Surge valves must react quickly via automatic control when an imminent surge event is detected, and the control signal is activated.
Compressor manufacturers’ dynamic testing parameters specify a maximum time from cut off (i.e. when the valve is fully closed) to fully open. This is typically around 2 seconds. Another specified parameter is the time taken for the valve to move from cut off to 80% open. The target timeframe for this is generally 1.5 seconds.
Opening time specifications are inclusive of dead time (the delay between the control signal being sent to the valve and the beginning of the valve response). It’s common for dead time to be allocated its own required value. For instance, the preferred time might be 0.3 seconds and the maximum allowable time 0.5 seconds.
Validating precision control
When a valve’s ability to quickly achieve the ‘fully open’ position is critical for safety, it is only necessary in emergency surge prevention situations. Much of the time a surge event can be avoided via carefully modulated control of the Anti-Surge Valve. In fact, opening too far may result in an excessive amount of compressed gas being recycled, which is wasteful and harms efficiency.
That’s why dynamic testing also assesses a valve’s ability to achieve precise movements without too much overshoot (when the valve moves more than required) or stiction (when plug travel is jerky due to friction). Proving that any overshoot or stiction are minimal provides assurance that the valve can achieve accurate, precision control in high‑speed surge prevention scenarios.
Take the Baker Hughes dynamic testing specification. This compressor manufacturer describes one test for valve moment involving continuous changes in the control signal from ‘98% opening’ to ‘2% opening’ over a five-minute period. Stiction of less than 1% is preferred, and the maximum allowable stiction is 1.5%. In other words, the test looks to identify whether friction causes any significant deviation between input signal and the valve’s position.
Need support selecting or sizing an Anti‑Surge Valve?
Demonstrating Stability
As well as maximising efficiency, smooth operation of Anti-Surge Control Valves is vital to avoid compressor surge being caused inadvertently.
Oscillation (repeated overshoot and correction), or the use of extra force to overcome stiction, can destabilise the compressor, pushing it into surge rather than avoiding it. What’s more, a valve that responds too aggressively to small, high-frequency signal variations may be overly sensitive to noise and mechanical vibrations in nearby equipment, including the compressor. If the valve moves unexpectedly and unintentionally due to environmental factors, resultant pressure fluctuations could be hugely detrimental to compressor performance and the wider liquefaction process.
Frequency response testing plays a critical role here. It shows how quickly the valve opens and closes in response to control signals at different frequencies, identifying whether it overshoots or oscillates. Tests demonstrate the sensitivity and linearity of the valve and actuator assembly, showing whether they respond accurately to small control inputs.
Bigger valves, better control
The 30” Anti-Surge Control Valve demonstrated exceptional speed, precision, and stability in dynamic testing. Results show that our bespoke valve design coupled with sophisticated actuation allows large valves to operate reliably and safely within a centrifugal compressor’s maximum efficiency zone.
Severn’s experience supplying technically challenging control valves for critical equipment enables us to meet customers’ safety and efficiency requirements without compromise. Our engineering team specialises in custom anti‑surge valve solutions for LNG, FPSO units, gas pipelines, compressor stations, petrochemical facilities and power generation plants.
Check out our previous articles which look specifically at the customisation of valve trims and control optimisation to facilitate this high level of performance. Or contact us to find out how valve engineering expertise can benefit your LNG project.
Large LNG compressor problems require large Anti-Surge Valves which in turn present complex engineering challenges. Valves with shorter travel (the distance the plug moves) and suboptimal control compromise the efficiency and reliability of the compressor. But traditionally, it’s difficult to control valves with a long stroke involving more than 12” of travel.
With extensive experience developing Anti-Surge Valves, Severn Valves resolves these challenges. Our expert valve selection, integration, setup and calibration enable large valves with up to 24” of travel to meet stringent performance and safety specifications.
Severn’s Anti-Surge control valves act extremely fast – within a two-second window – when process upset is detected on an LNG liquefaction train.
To facilitate a rapid inflow of surge gas, these valves typically have an oversized capacity of 1.8-2.2 times the maximum volume they are likely to handle. However, this important safety feature has implications for valve size, weight, and travel.
It is harder for large Anti-Surge valves to achieve the balance of speed and precise control required for compressor protection and optimal flow management. To compensate for this, LNG surge management systems involving large valves are often configured so that valves are activated at a lower threshold. This approach ensures plant safety, but it can compromise plant efficiency.
The whole valve package: focusing on the trim, actuator, and positioner improves operability
Severn’s proven Anti-Surge Control Valve technology takes a complete, highly engineered approach to overcome performance challenges for optimally selected valves where travel exceeds 12”.
Our bespoke valve trims for precise pressure let down, are integrated with sophisticated, carefully selected actuators and positioners. The impressive power and controllability of the actuation package is an integral feature of our valves. Precision control is enabled using high-power piston actuators which ensure a rigid and robust instrumentation setup. This enables us to implement a longer stroke – giving better control of the surge management process – while meeting the application’s exacting requirements for speed and accuracy.
The entire valve assembly is expertly integrated and calibrated as a complete system to deliver optimum performance. Valves are tested using a Profiler tool which measures and validates performance according to the specific Anti-Surge specifications. The tool is independently calibrated, ensuring valve performance is verified against end user standards without concession.
Our experienced valve engineers leverage test outcomes to fine-tune the actuator, positioner and boosters. Treating the Anti-Surge solution as a system of carefully selected, finely orchestrated components facilitates optimised, compliant valve performance.
Control optimisation boosts LNG productivity and efficiency by reducing the LNG Compressor Problems
As the below graph indicates, when compressor Anti-Surge Valves are primed for speed, accuracy, and reliability, liquefaction trains can operate within the compressor’s maximum efficiency zone. The entire LNG plant benefits from this. Controlling surge quickly and safely without it escalating into a major event allows operators to maintain higher liquefaction flow/pressure rates which boost overall productivity.
Severn’s Anti-Surge Control Valve technology enables this balance of speed and accuracy to be achieved consistently, even with large valves. With our ongoing commitment to R&D, Severn carried out stringent Anti-Surge specification testing on a valve with a nominal bore of 30” and a linear stroke of 24”. It performed the full 24” stroke in less than two seconds and achieved incredibly precise positional control ensuring specifications can be met without concessions on all valve sizes.
Bespoke trim designs optimise compressor Anti-Surge valves for the specific application demands of the LNG plant where they’re installed.
Internal components of a valve that come into contract with process media is collectively known as the trim. They are critical to its reliable operation. This is especially true of Control Valves that protect centrifugal compressors from surge events on LNG liquefaction trains.
Compressor Anti-Surge Control Valves are often exposed to high flow velocities. Severn’s Repair Intelligence data (based on our engineers’ analysis of historic OEM valve products) shows this can lead to severe operational issues including high noise levels, vibration, erosion, and premature failure. These problems bring the risk of safety issues, production loss, and unscheduled shutdowns. Spiralling costs can be incurred too, due to frequent maintenance and replacement of damaged parts.
Since process conditions vary considerably between LNG projects, tailoring compressor Anti-Surge Valve trims to handle specific gas flow characteristics is highly advantageous. As well as facilitating precise and reliable control, this enhances valves’ ability to endure the operating conditions, improving longevity and reducing potential maintenance and safety concerns.
Customising Compressor Anti – Surge Valves for Endurance and Performance
To enable the release of process gas, Anti-Surge Valves are sized (as per specification) to have 1.8-2.2 times the required capacity for the process conditions. This ensures enough gas is supplied to the compressor to prevent surge and avoid a trip situation. Due to the high velocities created by the process, the gas must be carefully controlled, and the trim fulfils two main duties. The first is to enable the controlled release of the process gas that can cause the compressor to go into surge. The second is to control the velocity of the gas passing through the valve.
As well as having potential to cause erosion, the velocity of the gas can result in high aerodynamic noise levels which may exceed acceptable plant limits. High noise levels are also indicative of vibration within the trim which may affect the valve and downstream equipment, potentially inducing various modes of failure. Lagging the pipework is often seen as a solution, but this does not address the root cause. It is more effective to optimise the valve trim for the process conditions.
Severn’s bespoke trims optimise surge gas control
Severn’s Anti-Surge Control Valves benefit from engineered solutions to address the high capacity and velocity control requirements of the application. Trim components that benefit most from engineer-led customisation are the plug and the cage.
Precision engineering of cage geometry, informed by Severn’s expert analysis of flow conditions and Repair Intelligence insights, improves valve responsiveness and overall control. For instance, the 3D flow path of the cage can be engineered to reduce deadband and improve controllability. Our Multi Labyrinth Trim (MLT) can handle up to 48 stages of velocity reduction and our 1CC trim offers a high-capacity option which maximises throughput. To balance the need for high capacity and precise velocity control, we have also developed the Vari-Stage Trim which can be configured to meet end users’ exact process requirements.
A valve’s cage helps to balance pressure and reduce turbulence as the plug lifts and surge gas enters. Even so, there can be a delay in the equalisation of pressure in the area above the plug with the changes below it. This can lead to severe vibration and instability if the system does not respond in adequate time.
Severn’s Repair Intelligence has identified that process forces acting on a valve plug can severely detract from valve performance in operation. To combat this, we have developed a ‘Waggon Wheel’ plug design, in addition to our standard options, which can be implemented where conditions dictate. The design ensures process forces are equalised across the plug allowing for rapid movement and accurate control.
All these solutions are designed and engineered using Severn’s robust sizing and selection process, technical expertise, and years of Repair Intelligence.
Valve engineering expertise
Severn’s Anti-Surge Control Valve Technology is rooted in an adaptive design process led by experienced engineers. Applying our valve engineering expertise to compressor Anti-Surge challenges on an application-by-application basis results in durable, highly functional valves which ensure reliability, efficiency and safety.
Contact us to find out more.
Severn Glocon UK Valves Ltd is a world leader in the design and manufacture of severe service Control, Choke and Butterfly valves. For clients in Scotland and operating in the North Sea, Severn Aberdeen based in Portlethen, serves as the regional hub for both OEM valves sales and service support whilst also offering comprehensive third-party valve support for the energy sector, oil & gas operations, and critical industrial applications.
OEM Control, Choke and Butterfly valve Support
As an integral part of Severn Glocon UK Valves, Severn Aberdeen specialises in sales and service support for Severn’s Control, Choke and Butterfly valves. These valves are specifically designed for severe service conditions, ensuring reliability, precision performance and longevity. The engineering expertise that Severn Glocon UK and the Aberdeen facility has allows the team to tackle the most challenging environments, providing clients with performance and reliability they can trust for offshore platforms, marine environments, and high‑pressure systems.
Third-Party Support
Beyond OEM support capabilities, Severn Aberdeen extends its capabilities to third-party manufacturers. Whether you’re dealing with Control, Isolation, Pressure safety (PSV’s) or Pressure Relief Valves (PRVs), the Severn Aberdeen team provides expert sales and service. This ensures our clients has a one-stop facility for their complete valve management, from procurement to servicing, across a wide range of valve types for asset integrity, regulatory compliance, maintenance optimisation, and reliability improvement.
Engineering Expertise at Your Fingertips
Severn Aberdeen’s unique advantage comes from being part of an Original Equipment Manufacturer (OEM). This allows the team to offer unparalleled engineering support to operators and EPCs. Clients can witness their valves and actuators being stripped, tested, and reported onsite while consulting directing with Severn’s expert engineering team for immediate problem diagnosis and resolution. This hands-on approach ensures transparency and rapid decision-making, keeping projects on track for clients seeking fast turnaround, reduced downtime, and specialist valve engineering support.
Complete Testing, Overhaul, and Offshore Support
Severn Aberdeen offers a full suite of testing and overhaul services at the Aberdeen facility. In addition, there is a team of certified valve technicians and offshore containers for offshore TARs (Turnarounds) and onshore shutdowns. This ensures smooth, seamless operations with minimal downtime, reducing the impact on your product schedules and maximising efficiency for shutdown planning, maintenance campaigns, North Sea operations, and complex valve lifecycle management.
Why Choose Severn Aberdeen?
- Expertise across extensive valve product types.
- Unmatched engineering support.
- Comprehensive service capabilities.
- Local support for Scotland and North Sea region.
Partner with Aberdeen for all your valve needs – OEM or third-party – backed by world class engineering and service support trusted by major operators, EPC contractors, and energy companies worldwide.
Contact the Aberdeen team today to discuss how we can optimise your operations and help you achieve your core imperatives of safe operations and minimum downtime: sales@severnvalve.com