A Technical Overview of Design, Safety, and Corrosion Considerations of Butterfly Valves Tackling Galvanic Corrosion in Fire Water Systems

Galvanic Corrosion: The hidden risk that provides costly challenges for operators

Thankfully strict safety protocols have been put in place by operators, meaning the greatest problem for these butterfly valves is failure due to corrosion rather than through heat. An increasing number of assets are seeing the failure of these critical valves after a few years. Up to now the solution has been to replace the valve like for like and implement a maintenance schedule as part of the planned TAR’s. This is not only inefficient but can be expensive. But, with the graphite isolated solution of Severn’s OCT-SW valve, there is now a superior solution.

What is Galvanic Corrosion?

Galvanic Corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte (e.g., seawater). The more active (less noble) metal corrodes preferentially.

• Graphite: Highly noble and acts as a cathode.
• Metallic Valve Components: Act as the anode and corrode.
• Result: Accelerated degradation of valve components, especially at sealing interfaces.

Nobility of materials

The term “nobility” of materials refers to a material’s resistance to corrosion, oxidation, and other forms of chemical degradation. Noble materials, like gold and platinum, are highly unreactive and do not easily combine with other elements. Conversely, “active” or “base” materials, such as iron and zinc, are more reactive and prone to corrosion. 

Galvanism can be traced back to the 18^th century when physician Luigi Galvani discovered that an electrical current could be created from a chemical reaction. His research laid the groundwork for the study of chemical electricity, or “galvanism”.

Following Galvani’s work, Alessandro Volta invented the first battery by stacking discs of two different metals separated by a salt-soaked material. This demonstrated that a sustained electric current could be created from the chemical interaction between dissimilar metals in an electrolyte. Scientists soon made the link and established this phenomenon to corrosion. They discovered that when two dissimilar metals were in electrical contact and exposed to an electrolyte (like saltwater), one metal would corrode more quickly than it normally would, while the other would be protected. 

The modern scientific concept of nobility is derived from centuries of practical human experience with different metals. 

The Galvanic Series

• Ranking by potential: The empirical observation of this galvanic effect led to the development of the galvanic series (or electro potential series). In this series, materials are ranked from “active” (most reactive and prone to corrosion) to “noble” (least reactive and most resistant to corrosion).
• Electrode potential: This ranking is based on a material’s electrode potential, which is a measure of its tendency to gain or lose electrons. More active metals have a lower (more negative) potential, while noble metals have a higher (more positive) potential.

 Today, engineers and scientists use the galvanic series to predict how different materials will interact in a corrosive environment. By understanding how this process works. Appropriate materials can be selected or ideally removed to stop the galvanic corrosion happening.

The Issue With Valves….

The use of graphite as a sealing mechanism is widespread across numerous industries due to its excellent sealing properties, chemical resistance, and ability to withstand extreme temperatures. However, in marine environments, particularly when exposed to seawater, its highly noble (cathodic) nature poses a significant risk of galvanic corrosion to the less noble (anodic) metallic components it contacts. This phenomenon is a major concern for offshore and maritime operators, as it can lead to compromised seal integrity, costly equipment damage, and unplanned downtime.

In a seawater-exposed assembly, a metallic component—for instance, a stainless-steel flange or valve stem—acts as the anode. The adjacent graphite gasket or packing acts as the cathode. The seawater completes the electrical circuit, drawing electrons from the less noble metal (the anode) and transferring them to the more noble graphite (the cathode). This leads to an accelerated dissolution of the anodic metal, concentrating the corrosion damage at or near the seal interface.

A particular concern is the combination of graphite with stainless steels. While austenitic stainless steels (e.g., 316L) are generally more resistant to corrosion, they are not immune. Some industry standards, such as NORSOK, even prohibit the use of graphite in sealing materials for offshore applications to eliminate this corrosion risk. Material selection is critical for valves on this duty. By utilising materials like Super Duplex or Aluminium Bronze, using hard facing on critical sealing faces and hard wearing seal materials, Service life for this critical application can be significantly increased.

Engineering Out Corrosion

The most definitive solution to prevent galvanic corrosion is to remove the graphite seal and replace it with a non-conductive alternative. Recent developments in sealing technology have introduced advanced materials specifically designed for demanding seawater applications where galvanic corrosion is a risk.

Modern valve designs, such as the Oblique Cone Technology (OCT-SW) Triple Offset Butterfly Valve, have been engineered to ensure graphite parts do not come into contact with the seawater, effectively isolating the corrosive elements from the line media and have solved this issue with patented and advanced Butterfly valve technology. The shift toward graphite-isolated technologies represents the most robust and sustainable solution for ensuring safety, extending equipment life, and reducing maintenance costs in demanding and safety critical seawater applications.

Initial Investment vs overall cost of ownership

It’s often a false economy with the old saying that “buy cheap, buy twice” but the cost and implications of buying cheap can be much worse. Greenfield sites can often be driven very much on cost, with the priority of building the new platform or vessel being that if it meets specification, lets buy the cheapest. But is the specification right and is the most cost effective to buy, the most cost effective overall?

Wrongly specified valves can often fail prematurely due to poor material selection or even be designed as throwaway items designed to last until the next TAR or service interval. But what happens if they don’t last and fail prematurely? What is the true cost unplanned downtime of replacing the valve on a critical safety system such as a fire water line.

Worst case scenario is that operations must stop, if it’s not safe to operate, production can be halted resulting in $millions in lost production until the valve can be replaced. If it’s deemed that it’s safe to operate, but the valve must be replaced urgently, mobilising costs, replacement valves, and the logistics of shipping valves offshore can run into hundreds of thousands of dollars.

All these costs and risks can be mitigated, by investing in the best solution initially, or for existing plants to upgrade to a better solution. By selecting a valve that’s been designed specifically for the application and materials that have been optimised for the media, unplanned downtime can be a thing of the past.

Severn’s OCT valve has been designed to be repaired and not replaced. The highest cost of the valve is often the main components such as the body and disc, often the best material for seawater service is exotic materials such as Super Duplex, Aluminium Bronze or can even extend to Hastelloy’s and Titanium for more severe applications where issues are known. By protecting the critical sealing surfaces by hard facing, it means that when the valves do need to be serviced, it can be done by replacing soft goods only, not just once, but time after time.

The engineered design of the OCT-SW means that valves can be overhauled on site with only basic tools, valves can be removed from line, overhauled and re-installed within hours. By repairing the valve, it also reduces waste and helps the operators meet ESG targets. It also further reduces costs associated with waste management and shipping waste back onshore. In summary, investing in the correct and most appropriate solution from the outset, may cost a little more that the “off the Shelf one size fits all” solution, but the overall savings could be millions.

Conclusion

Firewater systems are mission-critical safety assets. Every component must perform under extreme conditions—especially Isolation valves. Specifying fire-safe certified and corrosion-resistant valves is essential for:

• Personnel Safety
• Asset Protection
• Regulatory Compliance
• Operational Continuity
• Reduced Downtime
• Managing Environmental Risks

Severn Glocon’s OCT-SW valve exemplifies how advanced engineering can deliver robust, long-term solutions for offshore & coastal facility firewater systems. This solution can not only significantly reduce the overall cost on ownership and increase service life, but more importantly increase plant safety and reduce risk.

Fireproof Assurance: Severn’s OCT TOV Butterfly Valves Exceptional Fire Safety Design and Testing Credentials

As part of a safety-first approach Severn incorporates into its innovative Oblique Cone Technology (OCT) Triple Offset (TOV) Butterfly valve, fire safety is a critical part of that safety first objective. Fire testing standards state the minimum requirements the valve must achieve in order to receive fire safe certification. The standards dictate the setup & parameters required to simulate the conditions a valve may be subjected to during a fire, and test to ensure the valve can operate satisfactorily afterwards.

To summarise, the test consists of a valve being mounted in a fire test rig to flow water through the valve, and measure leakage both internally past the seal as well as externally through the packings and gaskets. The valves are then pressure tested at ambient temperature, once the valve has passed this element of the test, any leakage is recorded. The valve is then subject to a simulated fire by use of gas burners, with average temperatures of between 750°C & 1000°C recorded by thermocouples for the 30-minute burn time. Once complete, the flames are extinguished, and the valve is subjected to a forced cooldown using water to simulate the fire being extinguished on site.

The leakage during fire is measured and recorded. The valve is then subject to a re-ambient temperature and operational test, with the maximum leakage requirements being defined within the relevant standard. The tests are carried out in both the preferred and reverse directions and are witnessed by a 3^rd party approval body to give added confidence that the valve will perform as required in either flow direction.

By investing in and developing their own on-site fire test facility, Severn can understand and interpret the results to re-design & develop the fire safe valve technology for the OCT TOV Butterfly Valve, to further exceed the requirements set out in the standard. By doing this, Severn have been able to achieve up to Zero seat leakage, even after fire testing, giving further confidence to the capabilities of the valves when installed and further ensuring safety first is achieved for the end user and their operations.

The key to Severn’s success lies in their patented Oblique Cone Technology (OCT), which received approval from the UK Intellectual Property Office in 2018. This innovative design uses an ‘infinite circle’ geometry that allowed the research and development team to develop the circular sealing geometry, which gives the flexibility to use the valve for both isolation and control duties with the option of interchangeable seals and control trims.

Utilising its over 60 years of engineering heritage, Severn have designed and developed the innovative OCT TOV Butterfly Valve, a valve that meets the requirements of API 6FA, API 607, and ISO 10497 fire testing standards. These bi-directional isolation & control valves offer repeatable zero leakage, providing peace of mind for operators while ensuring safety is at the forefront.

Severn’s certification for fire test covers the OCT Laminate, Hybrid (OCT-HS) and Seawater (OCT-SW) seals, achieving the required leakage rates in accordance with the relevant international standards. By designing, developing, and testing the hybrid seal (OCT-HS) Severn have been able to understand how the hybrid polymer metallic seal acts under extreme temperatures, which has enabled them to develop a graphite free, firesafe seal, that works even after being exposed to the extremes of a fire test. By using this knowledge, the OCT-SW utilises the hybrid seal technology and prevents any graphite from contacting with the line media, therefore on seawater service eliminates galvanic effects and extends the service life of the valve.

By meeting stringent fire test standards, they have provided customers with a reliable and efficient solution to fire safety. With their patented oblique cone technology, Severn have set a new benchmark for future valve designs and innovative technology and further ensure the end user achieves its core remit of safe operations and reduced downtime.

Exploring the innovative features and engineering principles of Severn’s OCT TOV Butterfly Valve that puts safety first.

At Severn, safety is paramount in the design of our products. With our background in safety-critical industries, Severn understands the importance of safety first for both our customers and employees.  

As well as adhering to the strictest industry standards, Severn have identified that shaft blowout prevention was paramount to our end users and the wider industrial and process industries for improved valve performance and reduced operational downtime.  

Butterfly Valve shafts are designed to connect to the disc with either dowel pins, taper pins, or keyways. The separation of the shaft and disc in service can be catastrophically dangerous. If any of these parts fail, the shaft may be ejected from the valve body. Shaft blowouts can occur when a coupling mechanism fails, therefore, disconnecting the shaft from the disc. With the pressures in the system, it may eject the unrestrained drive shaft through either end of the valve.  

Not only is this projectile a huge safety concern but has the potential to compromise the pressure envelope of the valve allowing process to escape into the atmosphere.   

Severn has designed all their Triple Offset Butterfly Valves as standard with anti-blowout incorporated at both ends of the valve. This negates any chance of the shaft blowing out if the pins were to fail. The reduced shaft diameter at the drive end ensures the shaft cannot blow out through the packing follower.

On the blank end of the valve, Severn have multiple features which prevents shaft blowout. The anti-blowout ring on the threaded shaft end ensures positive engagement without the need for additional fasteners. The blank end plate is locked in place and is designed to withstand full rated test pressures.  

Dual anti-blowout devices are standard on the OCT TOV Butterfly Valve, meaning that even if the gland is removed, the secondary internal anti-blowout device will stop ejection of the shaft under the pressure, thus increasing both operator and plant safety. 

Severn have designed their Triple Offset Valves to exceed the minimum wall thicknesses stated in ASME B16.34. Instead of just using the minimum allowance, Severn have gone above and beyond to ensure the safety of our products in the field for our customers.  

Within Severn’s Triple Offset Butterfly Valve is a corrosion allowance. This means that the valve can afford to concede material to corrosion over time without affecting the pressure containing integrity or safety of the valve. The amount of corrosion may vary depending on the environment the valve is working in, but due to Severn’s engineering heritage and excellence, the OCT TOV Butterfly Valve has been designed to withstand changes in working environments and process conditions.  

High MAST figures and safety factors are key when designing the Triple Offset Butterfly Valve. MAST is the Maximum Allowable Shaft Torque a quarter turn valve shaft can withstand during operation without mechanical failure. With Severn using higher MAST figures on their Triple Offset shafts, this helps maintain the structural integrity of the valve.  

Sizing actuators correctly is a credit to Severn’s engineering excellence. Actuators, gearboxes, or any form of obturator that drives a quarter turn valve must be sized correctly by using the correct input and output torques. By torque testing the physical products prior to final inspection, we can compare the physical torques against our theoretical torques to maintain accuracy and consistency across the range.  

Safety has always been at the forefront of Severn’s designs, and this is paramount in the 8500 Butterfly Valve range.