Stringent Anti-Surge Valves specifications can pose challenges for larger valves on LNG liquefaction trains. But Severn’s bespoke Anti-Surge Control Valves ensure efficiency and compliance.
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.
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.
Dynamic testing explained
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.
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.
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.
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. 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 compressors 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 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.
Anti-Surge control valves must 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
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.
GRAPH IMAGE
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.
Contact us to find out more.
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 – collectively known as the trim – 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 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.
Sophisticated Anti-Surge valve technology from Severn leverages advanced actuation capabilities to deliver precision control, maximising LNG plant efficiency, safety, and productivity.
Controlling centrifugal compressor surge is a fundamental aspect of efficient LNG production, and Anti-Surge Control Valves play a vital role.
Surge events can damage critical rotating equipment, harm plant performance, and result in costly unplanned downtime. Yet a conservative approach to surge risk management compromises plant efficiency and productivity by constraining the compressor’s operating envelope. Identifying an acceptable trade-off between these two extremes is increasingly difficult as trends in LNG production evolve.
The escalating challenge of LNG surge control
Challenges surrounding compressor surge control have become significantly more difficult in the quest for optimised efficiency. With global demand for LNG growing, the capacity of existing and future ‘mega trains’ is increasing. This requires larger valves sizes, which makes it harder to achieve fast, accurate control in anti-surge applications.
Surge events can occur within milliseconds and without warning, meaning Anti-Surge Control Valves must operate with exceptional speed and precision. However, fundamental principles of physics and engineering make it harder to achieve critical performance parameters as valve size increases. The mass of larger valves introduces greater mechanical inertia, so more force is required to control the travel of the plug (the main moving part). Handling larger volumes of gas also introduces significant dynamic inertia and pressure delays, further impeding valve response times.
On LNG plants where Anti-Surge Control Valve travel exceeds 18”, operators traditionally had to tolerate conservative surge control measures, compromising overall plant efficiency. Until now…
Raise the surge control line, boost efficiency
Severn’s latest innovation addresses issues associated with larger Anti-Surge Control Valves head on. Our engineers have applied their technical expertise to the development of a robust, highly engineered solution.
Benefits include fast operability, high controllability, excellent reliability, and extremely accurate valve control. This means the valves respond very quickly (in less than two seconds, including any deadband), without compromising controllability when surge is imminent. As the below diagram shows, these superior performance characteristics enable centrifugal compressors to operate closer to the surge control line, optimising performance and efficiency.
Severn recently completed testing on a proof-of-concept Anti-Surge Control Valve with a nominal bore of 30” and a linear stroke (the distance the actuator travels) of 24”. The valve specimen’s pressure rating was ANSI 150, and it was designed with a flow coefficient (Cv) exceeding 7700, in line with the process conditions of a typical Anti-Surge application.
Testing showed that the valve meets all required parameters of the world’s most stringent Anti-Surge specifications. A significant highlight was its ability to perform the full 24” stroke in less than two seconds while simultaneously achieving incredibly precise positional control. The exceptional performance enables accurate and reliable control close to the compressor surge control line, striking an effective balance between safety and efficiency without concession or compromise.
There is a great variation in centrifugal compressor process conditions, in terms of feed gas properties and operating parameters such as flow rate, pressure, and temperature. It follows that Anti-Surge Control Valves must be individually specified and designed to optimise compressor performance and, in turn, maximise LNG plant performance and efficiency. Future articles in this series will explain how technical aspects of our Anti-Surge Control Valve technology, such as control optimisation and trim design, are customised to meet specific application needs and requirements.
Meanwhile, if you’re looking for expert technical input on centrifugal compressor surge control or other severe or critical service LNG valve applications, contact us at sales@severnvalve.com
Severn has a strong track record in the design and manufacture of valves that overcome the most challenging technical issues. LNG projects we’ve supplied in the past include Ichthys and Gorgon.
With their direct influence on safe, economical plant performance, compressors are a vital component of the LNG liquefaction train. Protecting them from the ‘surge phenomenon’ helps avoid costly damage and unplanned downtime.
Centrifugal compressors are critical to LNG production, raising the pressure of feed gas so it meets the thermodynamic requirements of liquefaction. Highly engineered and complex in nature, they are also expensive – typically costing millions of dollars.
Under normal process conditions, the impeller within a centrifugal compressor rotates at high speed accelerating the flow of the feed gas. It’s important that the inlet flow rate is sufficient to maintain this forward movement and keep the gas flowing along the liquefaction train. However, changing process demands across the wider system can cause fluctuations, bringing the need for extremely fast and accurate mitigation measures.
What is ‘compressor surge’ and why must it be controlled?
The surge phenomenon occurs when inlet flow stalls because it is insufficient to overcome the high pressure at the compressor’s discharge point. This results in a reversal of flow which can trigger a surge cycle: compressed gas rushes backwards through the impeller, reversing the flow direction of the gas and thus reducing discharge pressure and potentially stalling the compressor. As discharge pressure lowers, forward flow resumes, only to be reversed again.
Compressor stall and surge events happen within a 20 – to 50-millisecond window without warning and, if left unchecked, a surge cycle will continue indefinitely. The extent and immediacy of any consequences depends on the frequency and power of the surge force, the vibrations it generates, and the temperature of the surging gas. Associated risks range from short-term performance issues to catastrophic failure of the compressor and lengthy, costly unplanned downtime.
LNG project owners and engineering, procurement, and contractors (EPCs) need to consider the following factors when making decisions about surge control:
- Surge damages the compressor, compromising performance
A surge can damage compressor seals, with their replacement costing tens of thousands of dollars. Surges can also cause significant mechanical damage to bearings, the impellers or the shaft, and other critical components. As well as hindering the plant’s operational efficiency, a damaged compressor is more prone to leakage, posing a serious risk to safety and the environment.
- Consequences of compressor surge can lead to LNG plant shutdown
Stable operation is vital to the safety and efficiency of an LNG liquefaction train. Flow reversal can lead to major process-related problems requiring emergency shutdown. The repair or replacement of damaged compressor components can also necessitate downtime. Unplanned LNG plant shutdown has a major impact on production. It can lead to significant financial losses, possibly up to tens of millions of dollars, further highlighting the critical importance of a fast, accurate solution.
- Minimising the gap between ‘surge’ and ‘surge control’ maximises plant performance
Reducing the likelihood of compressor surge is critical. Yet, while a surge event can have serious consequences, an overly conservative approach to surge risk management constrains the compressor’s operating envelope, limiting overall plant efficiency. Effectively balancing risk requires a range of measures, from fast, accurate, dynamic control systems to predictive analytics and regular maintenance.
Severn has the solution to the enduring surge control challenge
Severn has engineered a sophisticated Anti-Surge Control Valve solution with advanced actuation capabilities to overcome this enduring challenge of LNG production.
Severn brings extensive experience in the design and manufacture of LNG valves for both the cryogenic and liquefaction phases of production. Previously, we’ve supplied severe and critical service valves for LNG liquefaction projects such as Gorgon and Icthys.
Contact us to find out how we can support your LNG development goals.
With a few weeks until IEW 25, Severn, a renowned leader in fluid control solutions, is thrilled to introduce the dynamic team of valve experts who will be representing the company at IEW 25 in Delhi from the 11-14 February.
As the world gears up for one of the most significant gatherings in the energy sector, Severn’s selection of experts promises to elevate the discourse on cutting-edge valve technology and innovation.
Join us as we unveil the names and expertise behind Severn’s delegation, offering a glimpse into the exceptional insights and knowledge they will be bringing to IEW 25.
Malathy – GM – Application Engineering – Oil & Gas, Offshore, FLNG, FPSO, FSRU
With over 19 Years of experience in the Oil and Gas Industry (specialising in Upstream & FPSO), Control Valves and Chokes with broad and specialised technical knowledge. Malathy brings a whole range of skills to the IEW team such as professional approach, decision-making, problem-solving, interpersonal skills, etc.
Alongside technical expertise, Malathy also has fantastic commercial acumen, winning large project orders, handling complex projects that involve new design and developments, special materials, quality, validation testing, etc., and possesses good exposure to International Standards (API, ASME, ISA, ASTM, and other relevant standards).
Malathy is currently working to expand the supply base of Severn products globally, especially in Southeast Asia, the Middle East Market, South America, Africa, etc., and is a fantastic addition to the Severn IEW 2025 team.
Kannan – GM – Application Engineering- LN, Hydrogen Power, Fertilizers, ASU & CCU
With 29 years of experience in the valve industry, Kannan’s knowledge expertise, and global awareness from working in multiple functions such as sales, application engineering, and project management have made him a respected figure in the Control Valve market with clients, earning him a reputation as a reliable and dynamic leader.
Kannan’s ability to anticipate market trends, build lasting relationships, and inspire his team is a testament to his unparalleled expertise and unwavering dedication to Severn, thus making him a valuable member of the IEW 2025 team.
Rajendran – Industry Manager – Application Engineering – LNG & Industrial Gas
Rajendran is a key account manager, focussing on enhancing the customer experience with key customers.
With 20 years of experience in the field of Control Valve Application Engineering and Project management, he is in charge of business growth from key account customers of the Oil & Gas and Industrial Gas segments. He established credibility in handling small to large size Project & OEM orders from other industry segments such as Refining, Fertilizers, and Water.
He is into leveraging Severn’s strength with core customers by establishing frame agreements and driving projects for process improvements, value stream mapping, and lead time reduction.
He is further assigned to diversify the business in new geographical segments by posturing collaboration and value proposition. His expertise in Oxygen service and Cryogenic Valve applications supports customers in their emerging process control and automation requirements.
Chandru – Manager – Application Engineering – Oil & Gas, Onshore, Refinery & Petrochemical
A seasoned Control Valve professional with a decade of expertise in the Oil and Gas Industry (specialising in Oil & Gas – Onshore, Refinery & Petrochemicals).
Chandru excels in delivering optimised Control Valve solutions to our customers (EPC’s and OEM’s) and is recognised by our customers for 24×7 consultation on any unique challenges / services related to control valves in their projects.
Alongside technical expertise, Chandru is adept at identifying market trends, commercial aspects and customer pain points, translating these insights into customised Control Valve solutions that enhance customer satisfaction and expand Severn Products’ Global supply base.
RK – Director – India Sales
RK joined Severn in 2017 as General Manager of Sales & Marketing to develop Domestic & Indian Subcontinent business.
With over 35 years total sales experience in process industries including Projects & MRO business, now as Sales Director of India region, RK identifies and captures new business opportunities with his strategic skillset and has delivered outstanding results, catapulting Severn to new heights in the Indian market.
With a proven track record of achievements in the Indian market, RK has become instrumental in driving revenue growth and expanding market share whilst forging lasting partnerships with clients and collaborators.
Gaurav – DGM – India Sales
Gaurav comes with a rich experience of two decades in the field of Sales & Business Development of Mission Critical Flow Control Products which play an important role in improving Process Efficiency, Uptime, Asset Management of an End User Process Plant together with Product Life-Cycle Management, New Market Developments thereby contributing to Organizations growth.
With Severn he is entrusted with developing the Project Business for our Severe Service Control Valves from Indian customers for both Domestic and International Projects through support of Field Sales Team with Severn’s values of Customer First, Integrity, Accountability & Excellence at the core of all the activities conducted.
Its our pleasure to invite you for a engaging discussion on business association, collaboration, emerging trends and flow control industry as a whole for a win-win relationship.
Sivakumar – Commercial Manager – MRO – Application Engineering
A seasoned leader in Valve Solutions bringing over 18+ years of experience in delivering top-tier solutions to industrial clients worldwide. My Journey in this field has been shaped by a strong foundation of technical expertise, customer-focused strategies, and innovative problem-solving. Comprehensive knowledge of valve industry processes systems, spares, and replacement strategies to optimize performance and reliability. Has a proven track record of diagnosing complex operational challenges and delivering efficient, cost-effective solutions. Deep understanding of client needs, ensuring tailored solutions that align with operational goals.
Leading a team committed to excellence in providing world-class on valves aftersales solutions. Our focus is on enhancing system performance, minimizing downtime, and ensuring our clients’ operations run seamlessly.
Sanjeev – Senior Manager – MRO – India Sales
With 17+ yrs of experience in Flow control industry, Sanjeev provides the techno-commercial expertise, clients relationship management, enhancing overall customer experience with after sales support, valves solutions for various customers within Oil & Gas Industry.
Sanjeev is overseeing MRO opportunities in India region, he is a trusted & well-versed with Severn’s core Control Valves products range & solution driven approach supporting end-customers to find solutions, enhance their efficiency, reliability and productivity, especially in severe services & challenging applications in process industries.
