Oil & Gas

Is it time to re-visit using perfluoroelastomer seals in your valves? First developed by DuPont™ in the late 1960s, perfluoroelastomers (or FFKMs), are now widely known and understood in a variety of markets. But for those that may be less familiar with these high performance materials, here is a quick recap…

What are perfluoroelastomers (FFKMs)?

They are essentially highly or fully fluorinated compounds with a fluorine content above 75%, and they offer outstanding chemical resistance. Generally better than all other elastomer types, FFKMs are often referred to as having the resistance of PTFE but in elastomer form. The term “universal” chemical resistance is commonly used; although it’s not strictly true as we will learn shortly.

Unlike PTFE, the molecular make-up of FFKM includes crosslinks (or spring-like elements). This is contrast to just a backbone of carbon-carbon atoms surrounded by protective fluorine atoms. These crosslinks are what give the FFKMs their crucial elastic behaviour (in other words returning quickly to their original shape after being deformed). But the crosslinks are also a drawback as they can be a weak point for a chemical attack.

Different crosslinking systems can be used when developing FFKMs and the choice will determine the high and low-temperature capabilities. Compounds developed for extreme high-temperatures (up to around 325oC) generally have a less broad chemical resistance. This is in comparison to the lower temperature grades (up to 225oC). Similarly, FFKMs developed to have excellent resistance to specific fluids (such as amines or high-temperature steam) can have limitations of low-temperature capability or compression set. As a result, there is no universal material that covers all application criteria bases.

A variety of grades

Previously the number of perfluoroelastomer grades was less prolific than other elastomer types such as FKM, EPDM, and NBR. However more than 50 years of technical developments have created a range of FFKM grades for specific and challenging applications. These are particularly in chemical process, oil and gas, semiconductor, and aerospace industries.

Additionly, options with a hardness range of 65 to 90 durometer, and versions that meet international standards or specifications for food, medical, CPI, and oil & gas applications means the portfolio of FFKM-based compounds available to engineers is now substantial.

In addition to technical developments, manufacturers and compounders have also been addressing the only real drawback of FFKM materials; the cost. They are difficult and time-consuming base polymers to manufacture.

With a relatively low volume production base and sometimes lengthy processing times, FFKM seals carry a high financial premium over FKM seals. Even several times greater than FKM itself has over NBR.

In recent years, there’s been more focus on making general-purpose grade FFKMs with broader temperature and chemical resistance capabilities more financially attainable. The initial procurement costs remain high compared to less capable elastomer bases. The overall cost of ownership may now be more appealing than it was twenty or even ten years ago. The ability of FFKM seals to survive for much longer in applications where exposure to a variety of fluids (perhaps wider than originally specified) is possible. This considerably reduces unplanned costs associated with maintenance and downtime.

Focus on dry coatings

The cost of unscheduled maintenance and repair in pump and valve equipment can be high in any industry, but exceptionally so in petrochemical, oil & gas, and semiconductor. When these costs are fully considered in the overall lifetime of a product, the initial price of seals in a valve is considered relatively minor, but it can still be a barrier in the material selection process.

With both technical and commercial developments in recent times FFKM materials now compare more favourably against other materials for static, or low-duty dynamic applications in valves. In applications where persistent and sporadic issues keep coming back to cause problems, they are now a more financially attainable choice of material to avoid re-work, overhaul, downtime, customer dissatisfaction, and ultimately, more costs.

Read more about FFKM as a suitable sealing material HERE

Our customer designs and manufactures a leading range of unique downhole technology and drilling solutions that contribute to a net zero energy industry.

The Application

A seal was required for the rod of a downhole drilling tool – a hydraulic dynamic (rotary) application. Our solution is a PTFE rotary seal. Read on to find out about more.

The application has a normal operating pressure of 500 PSI at 60 RPM, but maximum pressure can reach 6,500 PSI in static operation. Reverse pressure was unlikely in this application but the engineers wanted to ensure some level of resistance.

Two single acting seals were considered, but groove space is limited. Keeping the grooves closed is preferable for bearing strength.

The maximum operating temperature reaches 200°C and the application media drills mud and completion fluids (with wiper arrangement already installed).

Our Sealing Solution

Due to the pressure, temperature and chemical media parameters of this application, an elastomer seal selection was not suitable.

Our engineers selected our standard FTOR profile PTFE seal This is a double acting slipper seal ideally suited to hydraulic applications and capable of sealing under alternating pressure directions.

It’s ideal for sealing high pressure loads with slow to moderate rotational speeds. The PTFE rotary seal has side wall notches equally spaced, so the part can be fitted symmetrically either way.

The initial sealing force is provided by the elastomer O-ring. This is seated within a machined saddle and activated by system pressure to perform under high pressure demands. The central lubricating channel design ensures low friction and wear.

Additionally, the sealing set has been designed with a scarf cut PEEK back-up ring. This is to ensure stability and seal performance at maximum working pressure of 6,500 PSI.

Customer Satisfaction

Our customer tested the sealing arrangement at higher pressure (up to 10,000 PSI). Consequently, our customer is pleased it seals successfully over and above the application requirements. They have adopted this seal design for other sizes of parts in similar equipment.

Read more about our rotary seals HERE

With diverse applications in harsh environments, the Oil & Gas industry presents some of the most challenging demands on engineered sealing solutions. Our collaboration with Parker Seal Group allows us to integrate their materials and sealing expertise to meet our customer demands.

Characteristics of Oil & Gas sealing

Regardless of where seals are used in oil & gas applications, they are without doubt critical to the safe, reliable and efficient operation of a huge range of onshore and offshore equipment. There are many challenges involved in oil & gas application sealing; conditions typically include low and high temperature extremes, very high pressure conditions and most seals need to withstand aggressive fluids and media such as sour gas, salt water and super-heated steam.

There are three main sectors within  the Oil & Gas industry, with different processes and equipment requiring sealing solutions. Upstream; commonly known as exploration and production – this refers to the recovery of hydrocarbon reserves in the form of natural gas and crude oil. Midstream; refers to the processes involved in the transportation and storage of natural gas and crude oil, from production site to refinery location. Downstream; includes the processing of natural gas and crude oil at oil plants and petrochemical plants.

Well Drilling

This is the process of extracting oil and gas from beneath the ground, in both onshore and offshore environments. Seals used in these applications have to cope with increasingly harsh environments (with wells becoming deeper and deeper). System pressures up to 30,000 PSI and operating temperatures between -50°C and +220°C are common, and seals have to demonstrate excellent fluid compatibility and resistance against aggressive media – all with longer service life expectations.

Applications include; drilling and tool bits, blow-out preventers, drilling mud systems, LWD and MWD test equipment, casing and pipe connections, subsea risers and connector systems, control valves, compressors and pumps.

Seals need; high temperature and high pressure capabilities, sour gas and abrasive drilling fluids resistance, extrusion resistance and compatibility with well bore fluids.

Well Completion

This is the process of making a well ready for production after drilling. Similiar to well drilling, seals used in well completion must withstand increasingly harsh condition such as deeper wells and more diverse geographical areas with extreme hot and cold weather conditions. System pressures up to 30,000 PSI and operating temperatures between -45°C and +220°C are common, and seals have to demonstrate excellent fluid compatibility and resistance against aggressive media.

Applications include; tubing heads and hangars, packer assemblies, well controls, Christmas trees, cementing equipment, well head completion assemblies, well service.

Seals need; high temperature and high pressure capabilities, chemical compatibility (including H2S resistance), RGD & extrusion resistance and steam resistance.

Distribution

Following on from the production stage, petroleum products are transported to processing facilities and to end users in pipelines. Seals used in midstream distribution sector applications often operate in low temperatures, down to -196°C (required to liquify gas) as well as high temperatures of 480°C (to meet fire test requirements). System pressures can be as high as 10,000 PSI.

Applications include; marine and offshore loading swivels and turrets, railcar loading systems, pipeline service equipment (pigs and spheres), pipeline valves & actuators, pumps & compressors, tank & loading systems.

Seals need; Extrusion, corrosion and abrasion resistance, extreme temperature and pressure capabilities, chemical compatibility (including H₂S), RGD resistance, compliance with NORSOK, ISO and API specifications.

API 6A, NORSOK M-710, ISO 23936-2 and TOTAL material qualifications

The Oil & Gas industry has specific testing and qualification standards to ensure that materials used in harsh drilling and production environments meet the critical demands of these applications.

ISO 23936-2:2011 describes the requirements and procedures for the qualification of elastomeric materials in accordance with media related to oil and gas production. H2S testing in accordance with this specification enables the lifetime prediction of compounds.

NORSOK M-710 defines the requirements for critical non-metallic (polymer) sealing, seat and anti-extrusion ring materials for permanent subsea use. This includes well completion, christmas trees, control systems and valves as well as topside valves in critical gas systems.
API 6A is the specification for drilling and production, wellhead and christmas tree equipment.

Total GS EP PVV142 defines the requirements for non-metallic sealing materials concerning elastomers within pipeline valve applications.

In conjunction with Parker Seals we offer a range of products in materials that are qualified to these specifications.

We work closely with our oil & gas customers, read more HERE

Valves are imperative for isolation and control functions, and can be found in a broad range of industries such as Oil & Gas, Water & Wastewater, Food & Beverage and Hydraulics & Pneumatics. We supply seal products into valve applications in a variety of styles including ball, gate, flap, plug, butterfly, spool, check and solenoid valves.

Characteristics of valve sealing

There are many challenges involved in valve application sealing. Conditions and application parameters can vary with temperature extremes from cryogenic up to 325°C, and pressures up to 1000+ bar. We need to carefully consider the materials to suit all fluid compatibility required. Often the seal design requires low breakout friction and offers no stick-slip following prolonged static periods when the valve is not used.  Alongside this, customers require long service life and minimal maintenance.

Valve styles include ball, gate, flap, butterfly, spool, check and solenoid valves. Also different types of actuation include manual, pneumatic, hydraulic and electro-mechanical.

Different areas of the valve demonstrate different sealing requirements.

Valve sealing areas

Actuation

There are a range of sealing solutions to suit the variety of actuation types employed with valves. This includes diaphragms for pneumatic actuation, rotary and linear hydraulic and pneumatic seals, and gaskets and O-rings. Seal materials are available to suit all ranges of temperatures and media associated with the actuator and any external contaminants it encounters.

Body bonnet joint

This is a static sealing location that can often be sealed with an O-ring (a wide range of materials are available to satisfy fluid compatibility). However dependent on the fluid, pressures and temperatures, metal seals can be more suited to the application. Additionally, housing deflection under pulsating system pressures may worsen compression set sealing issues. Therefore, a custom gasket design could be potentially more suitable than an O-ring. For subsea valves, a sealing solution capable of handling alternating pressure regimes and multiple media types may be required.

Stem

A critical and dynamic sealing location with often demanding requirements. Depending on the application of the valve, the seals used here may see frequent dynamic operation and will require a long wear life. In other cases, the valve may be static for long periods and then require operation with minimal break-out friction forces. In all cases, reliable sealing is paramount.

Seat body

Valve seats are often mounted in a housing or carrier which has a sealed interface within the valve body and in these cases it can be a critical location to seal correctly. Dependent on the design, the seal location may be subject to upstream or downstream pressures at various points. In some cases fluid flow through the valve can pull or wash-out seals from their grooves if they are not designed to prevent this. As pressure conditions change with valve operation, the seals here may be required to withstand small (but sometimes frequent) movements of the carrier without sticking or wearing.

Valve Seat

A wide variety of elastomers and engineered polymer materials can be moulded or machined to suit valve seat components. Bonded rubber to metal or rubber to plastic seals can provide bespoke solutions. These offer benefits in terms of space envelope, component count or ease of assembly.

Design & Development for valve sealing applications

Our engineering team understand the application demands associated with valve sealing and can support our customers with the design of seals for every position within the valves.

We provide a complete design service; from initial seal geometry and profile choice, to material selection and prototyping, through to final production. This is utilised with our seal design experience and materials expertise, alongside technology such as 2D/3D CAD and FEA analysis. These simulate performance before finalising each individual seal design.

We are familiar with the requirements of individual markets and their valve applications. Our seals are manufactured in materials with approval requirements such as NORSOK M-710, ISO23936-2, NACE, WRAS and FDA.

For more on our design and engineering service, see our dedicated page HERE

The use of metal seals as an engineered sealing solution is appropriate where it is not possible to use elastomeric or polymer seals due to extremely demanding application requirements. For example, these could include applications with extremely high temperatures (300°C upwards) and pressures, intense radiation, cryogenic conditions or highly aggressive chemicals.

How do metal seals work?

The metal seal concept is based on plastic and elastic deformation of the seal during compression which creates a sealing interface. The metal seal is compressed in the cavity on average about 20% of its original free height. The force generated through compression of the ring produces a high contact stress at the seal/cavity interface. This force is then supplemented by the pressure-energisation force which rises in proportion to the increase in differential pressure inside the seal cavity.

What types of metal seal are there?

There are three types of seal energisation; self, spring and pressure energisation.  By design metal C-rings are self-energising due to the good spring back characteristic of the C-shaped profile. Additionally, they can be used in internal, external and axial pressure conditions.

The different base material characteristics and heat treatments, along with material thickness, and cross section of the seal also determine the compressive load. This is directly related to the sealing level achieved and is known as “self-energisation”. Spring energised seals have excellent spring back properties and are typically used to improve leakage rates by increasing the load on the sealing interface.

All metal seals can use system pressure to generate a hydrostatic load to obtain the highest level of sealing possible; this is known as pressure energisation. At high pressures this becomes an advantage and allows the design of metal seals for applications of 25,000 PSI and above.

Ultimate seal performance

Once the metal seal profile and material has been selected depending on the application, there are a variety of platings and coatings available. These can  modify the surface properties of the seal to create a malleable outer surface layer. Typically precious metals such as gold and silver are used for plating, but many other options are available with two common ones also being Tin or PTFE. This layer ensures optimum sealing despite any mating surface imperfections. The plated or coated layer also reduces coefficient of friction so the seal can slide and bed down during initial compression. Consequently, this prevents galling. As well as providing better physical properties to the seal, coatings and platings are chosen to withstand high temperatures and aggressive (often corrosive or oxidizing) environments.

There are ever changing industry demands and fast paced technology developments – particularly from customers in the Oil & Gas, Aerospace & Defence and Automotive markets. Therefore, we are challenged daily with applications where the boundaries are being pushed to the absolute limit. We have designed metal seals into F1 car exhaust systems, subsea repeaters, oil and gas production valves as a few examples; the capabilities of high performance metal seals is endless. Working with the latest developments in materials, platings and manufacturing technology; our engineering team design the sealing solutions to meet the complex specifications these types of application demand.

Learn more about metal seals HERE

Polytetrafluoroethylene (PTFE) is a thermoplastic polymer that can be used in a variety of sealing applications; it is particularly suitable where the application conditions exceed the parameters of elastomeric seal use, but are not as highly demanding as applications that require the use of metal seals.

What is PTFE?

Discovered accidentally in the DuPont™ laboratory in Jackson, New Jersey, USA in in 1938. The molecular structure of PTFE is based on a linear chain of carbon atoms which are completely surrounded by fluorine atoms. The carbon-fluorine bonds are among the strongest occurring in organic compounds. As a result PTFE has thermal stability across a wide temperature range.

It’s high melting point (342 °C) and morphological characteristics allow seal components made from virgin PTFE to be used continuously at service temperatures of up to 260 °C, and with the addition of fillers – up to 300°C. It has the unique ability to resist material degradation, heat-aging and alteration in its physical properties during temperature cycling. Alongside this rare combination of material characteristics PTFE also has unlimited shelf life.

Why use PTFE seals?

Notably PTFE demonstrates extraordinary chemical resistance: the intrapolymer chain bond strengths preclude reactions with most chemicals, thereby making it chemically inert at elevated temperatures and pressures with virtually all industrial chemicals and solvents. Only a few media (some molten alkalis) are known to react with PTFE seals making them the perfect sealing solution for highly aggressive chemical applications.

PTFE also has the lowest friction coefficient of any known solid; it has self-lubricating capabilities which offers continuous dry running ability in dynamic sealing applications and has superb stick/slip capabilities.

Focus on dry coatings

The advantages of using PTFE in sealing applications are; functionality at high and low temperatures, dynamic sealing with high wear capabilities, high pressure sealing (using combinations of PEEK back-up rings) and compatibility with highly aggressive chemical combinations.

Our range of PTFE seal products include back-up rings, rod and piston seals, slipper seals and spring energised seals in a wide variety of sizes. Materials depend on application requirements but we offer a wide range from Virgin PTFE or including filler combinations of MoS2, glass, carbon, carbon fibre, graphite, and bronze.

These characteristics make PTFE seals perfect for the demanding applications involved in Oil & Gas, Aerospace, Automotive and Chemical Process markets (to name but a few) and Ceetak’s engineering team are experienced in the design of PTFE sealing solutions to meet the complex specifications these types of application demand.

Read our overview and more detail about PTFE seals HERE