Discover how engineering excellence, and offshore flow control innovation have driven Severn’s OCT TOV Butterfly Valve to deliver unmatched reliability in seawater service valve applications and harsh offshore environments.

Severn’s research & development team has designed a Butterfly Valve for Seawater Applications that solves the problem of galvanic corrosion in offshore systems and meets strict firesafe valve standards. Utilising over 65 years of engineering excellence in industrial valve design, the team of technical valve specialists achieved this by using Severn’s patented Oblique Cone Technology (OCT). The OCT‑SW Butterfly Valve takes this proven control and isolation valve technology to the next level by eliminating the need for graphite in the seal while maintaining full firesafe performance required for critical offshore safety systems.

What is galvanic corrosion and its costly effects?

The impact of galvanic corrosion in seawater valve systems on critical offshore assets due to marine process conditions is an enduring problem for offshore oil & gas installations, FPSOs, and sealine infrastructure. At best, it increases maintenance workload and repair activity during planned shutdowns. At worst, it can result in rapid or unexpected valve failure, leading to unplanned production downtime or emergency shutdowns.

Either way, galvanic corrosion presents a significant lifecycle cost risk that negatively impacts plant efficiency, operational reliability, and total cost of ownership. However, Severn has utilised its engineering heritage, in‑house R&D capability, and valve repair intelligence to develop a seawater butterfly valve solution that tackles galvanic corrosion head‑on.

Why does galvanic corrosion occur?

The cause of galvanic corrosion (also referred to as dissimilar metal corrosion or bimetallic corrosion) is an electrochemical reaction between two different conductive materials in close proximity within an electrolyte, such as seawater processing systems. One material – typically the least noble – is preferentially corroded.

In offshore valve design, the classic rule of “do not mix metals” is difficult to achieve due to extreme environmental conditions, fire safety requirements, and stringent materials specifications.

Modern offshore safety systems, such as firewater systems, must withstand continuous exposure to corrosive seawater, while delivering reliable isolation and control valve performance during normal operation and emergency conditions. Seawater service valves therefore play a critical safety role, making the elimination of galvanic corrosion while maintaining firesafe valve certification a long‑standing industry challenge.

The graphite challenge in seawater valve applications

In recent years, graphite sealing technology has become widespread in industrial valve manufacture due to its excellent thermal resistance, chemical stability, and flexibility. However, graphite is also the only non‑metallic electrical conductor and is more noble than many metals commonly used in offshore valve construction, including stainless steel, bronze, and titanium.

As a result, when graphite is exposed to seawater in contact with these metals, it can accelerate galvanic corrosion, particularly within seawater butterfly valves, control valves, and firewater isolation valves.

Traditionally, Severn’s Triple Offset Butterfly Valves utilised graphite in parts of their construction, which in seawater service applications could contribute to galvanic corrosion. Over time, this may compromise sealing integrity, valve reliability, and plant safety, potentially leading to costly unplanned outages.

Engineering a long‑term seawater valve solution

By working closely with offshore operators, EPC contractors, and end users, Severn identified this challenge and applied its extensive engineering heritage and technical valve design expertise to develop a long‑term solution.

The Severn engineering team designed a valve that either eliminates graphite entirely or isolates it completely from the line media, significantly reducing the risk of galvanic corrosion during normal operation. This ensures the highest levels of operational safety, asset protection, and system reliability, supporting the industry’s requirement for safe operations and minimal downtime.

OCT‑SW Triple Offset Butterfly Valve for Seawater & Firewater Systems

Severn’s OCT‑SW Triple Offset Butterfly Valve is a high‑performance seawater valve solution developed specifically for offshore sealine applications, firewater systems, and marine utility services.

These valves play a pivotal role in offshore safety systems, particularly where rapid isolation, reliable shut‑off, and firesafe operation are mandatory. Leveraging over 65 years of oil & gas valve engineering experience, the OCT‑SW valve has been designed to help operators meet their core objectives of safety, reliability, and reduced downtime.

Hybrid metallic‑polymer sealing technology

Severn has developed a hybrid polymer‑metallic sealing arrangement that removes the need for graphite laminates. By combining a primary metallic seal with a secondary polymer seal, Severn has:

• Eliminated graphite exposure to seawater
  Increased isolation valve sealing performance
  Maintained full firesafe valve certification

Furthermore, by ensuring that any remaining graphite gaskets and packings are fully isolated from the process media, the design prevents graphite and seawater from ever coming into contact. This eliminates galvanic corrosion risk, protecting production uptime, asset integrity, and operating efficiency.

Certified firesafe and ATEX‑compliant valve design

In addition to mitigating corrosion, Severn’s Butterfly Valves for Seawater Applications meet key firesafe testing standards, including:

• API 6FA
• API 607
• ISO 10497

This confirms the OCT‑SW valve as a certified fire‑safe valve, suitable for critical emergency scenarios.

The design also complies with ISO/IEC 80079‑36:2018 (ATEX) requirements, ensuring that static charge build‑up is eliminated and preventing any risk of spark generation. This makes the valve suitable for a broader range of hazardous area applications, extending beyond seawater service and reinforcing its versatility.

Materials, retrofitting & offshore suitability

The Severn OCT‑SW Butterfly Valve can be manufactured in a range of corrosion‑resistant materials, including:

• Aluminium Bronze
• Super Duplex Stainless Steel
• Titanium

Anti‑blowout protection is provided as standard. Available in standard and non‑standard face‑to‑face dimensions, with lugged and double‑flanged body styles, the valve can be easily retrofitted into existing offshore pipeline systems. This makes it an ideal upgrade solution for operators experiencing galvanic corrosion issues in seawater valve systems.

Operators are under increasing pressure to reduce fugitive emissions for both onshore and offshore assets in order to achieve their core imperatives of safe operations and minimum downtime. Severn realises the role they play in today’s climate conscious world to help reduce and eliminate fugitive emissions from valves. Utilising the engineering heritage and extensive knowledge in severe service applications, Severn ensures it can offer the most suitable product for the end user.

Through Severn’s ‘Repair Intelligence’ and close operating relationships with end user operators, Severn has been able to understand the difficulties facing operations in the specification, purchasing and servicing of Control, Choke and Butterfly valves that are critical to reducing fugitive emissions across industrial facilities. Severn prides itself in offering technical solutions that perform no matter how severe or critical the application is. Ensuring that the end user gains the best valve performance and reduced maintenance costs over the lifecycle of the valve.

It has long been understood that approximately 60% of fugitive emissions come from valves. Even more so 80% of those emissions are related to the stem/shaft seal. Naturally, the focus is on this area with the relative fugitive emissions standards such as API 622 and ISO 15848. What is often misunderstood is the requirement for the standards to be applicable across varying temperature and pressure differentials. For this reason, Severn has 43 different certificates for sealing systems in valves based on their application requirements, up to 10,000 Psi and 425ºC. By utilising a range of materials from filled graphite through to custom PTEE-based compounds, Severn has, coupled with novel packing designs, been able to achieve tighter leakage rates that had previously been achieved with standard packing sets.

It is vital for the end user to understand the leakage class requirements when fugitive emissions are concerned to prevent over or underspecifying the solution. We often see “fugitive emissions” specified without clarification of the requirements. The various requirements from TUV through API and ISO specifications require different testing methodologies and even different testing mediums. This means that the testing standards are not directly comparable to each other. Severn often see the specification of “Low-e” or “Low emission” packing without reference to the specification. In some instances, these packing sets can have allowable leakage of up to 500ppm, many times that of systems tested to the ISO 15848-1 standard and potentially resulting in detrimental reduced on-site performance and / or higher maintenance costs.

Severn understands the ongoing challenges operators face with reducing and eliminating fugitive emissions and have created a technical solution with the design of its Oblique Cone Technology Triple Offset Butterfly Valve.

Severn has focused and will continue to focus its testing efforts on ISO 15848 standards as it is understood that these offer the widest range of qualification options whilst not utilising harmful greenhouse gases that can be emitted using some API methodology. The fact that sealing systems are tested on the valves they are designed for and not a standard test fixture ensures maximum customer confidence in our products performance and reliability.

Severn have focused on passing some of the most stringent testing with class A leakage classes and up to 40,000 operations available for some applications. Ensuring that performance is at the heart of our product range, and you achieve your core remit of safe operations and minimum downtime.

To further the commitment to reducing fugitive emissions and reduce the burden on end users to meet tightening specifications, Severns OCT Triple Offset Butterfly Valve offers the fugitive emissions packing sets as standard fitment on all standard valves in the range. Ensuring that the end user experiences maximum valve performance in all applications.

Severn’s engineering heritage and technical expertise have led to the OCT TOV Butterfly Valve being future-proof for changes in the process conditions to provide increased versatility for the end user seeking reliable high‑performance triple offset butterfly valves, industrial isolation valves, and severe‑service valve solutions.

From the outset, Severn made flexibility a key driving force in the design of the Oblique Cone Technology (OCT) Triple Offset (TOV) Butterfly Valve. Due to Severns extensive diverse engineering heritage and excellence, our expert team of engineers understand that processes and application product demands change over time, whether it is the process conditions or the overall requirements of the valve for the end user. Due to this understanding, the Oblique Cone Technology Triple Offset Butterfly Valve has been designed to incorporate multiple seal options, all fully interchangeable with each other, providing maximum application diversity and usability to ensure safe operations and minimum downtime making it ideal for oil & gas isolation, refinery valve applications, petrochemical process valves, and critical shutdown and control operations.

The Laminate seal is the “traditional” Triple Offset Valve seal and consists of multiple metal and graphite layers providing isolation sealing for high‑temperature, high‑pressure, and severe‑service applications.

The OCT HS seal is a hybrid polymer metallic seal, this seal benefits from a primary metal seal and secondary polymer seal, this provides a reliable and repeatable bubble tight seal time after time. This can also be paired with PTFE packings when graphite being in contact with the line media is a concern. The polymer seal is fully compliant with EN ISO 80079-36 (ATEX) making it an excellent choice for ATEX‑rated butterfly valves, hydrocarbon service valves, and zero‑leakage industrial valves.

The OCT SW Valve takes the hybrid sealing to the next level with its versatile high performance. Severn utilises the OCT-HS seal and has designed a valve that ensure there is no graphite in contact with the line media to remove the risk of costly galvanic effects such as internal corrosion leading to valve failure. Whilst doing so the OCT-SW also maintains firesafe certification making it suitable for Firesafe Triple Offset Valves, API 607 certified valves, and critical isolation applications in hazardous environments.

Should the sealing requirement not become as critical, and process conditions become more arduous, the Laminate and Hybrid seals can be changed for the OCT-SS solid seal. As the name suggests it is a solid metallic seal, that can be made from hard-wearing alloys to add longevity to the sealing life of the valve in arduous conditions and can offer a control valve seat leakage ideal for erosion‑resistant valve applications, abrasive service, and high‑cycle industrial operations.

Based on Severns comprehensive history of severe service control, our team of engineering experts work closely with operators and end uses to identify the correct seal and material selection to provide the maximum reliability and productivity further ensuring minimum downtime supporting industries such as LNG, chemical processing, power generation, and midstream pipeline operations.

All the OCT seals are interchangeable and can be upgraded without the need for main valve components being replaced, further emphasising the OCT TOV Butterfly Valves versatility. The fully in field serviceable valve can be upgraded on-site without the need for specialist tools or knowledge, this further ensures that costly unplanned downtime and site waste is kept to a minimum, along with potential loss in production for the end user. All the seal options can be changed on site within a small space of time to ensure site maintenance costs are reduced by upgrading the existing valve rather than discarding and replacing with a commodity product each time making it a cost-efficient solution for industrial valve maintenance, asset lifecycle extension, and retrofit valve upgrades.

Each OCT valve is specially designed to be versatile and ensure it has multiple purposes for multiple conditions whilst still delivering maximum performance. With the introduction of the interchangeable seal, these can be easily swapped out to match the end users’ requirements, should they change ensuring adaptability for future process changes, sustainability improvements, and long-term operational efficiency.