Triad offers a wide choice of soft seats and metal seated ball valves for a variety of industrial applications. Below is a general guide. When selecting seats, always consult the pressure / temperature charts and corrosion resistant guide or contact the factory for engineering help. Not all seats are available for use in all our valves.
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Made from Virgin Teflon, this is the most common sealing material; its chemical compatibility is excellent for almost all media. Temperature -50°F to 400°F.
PTFE Cavity filled Seats Available on request (CF), suitable for filling the void between the body and ball eliminating product build up. Cavity filled seats are standard on our sanitary line of ball valves in both two and three way.
15% glass reinforced PTFE, suitable for temperature -50°F to 450°F, chemical resistance is compatible to virgin PTFE with better wear factor. The standard in most all of our ball valves.
25% Carbon Graphite with 75% PTFE, this material offers a wide temperature range with better wear resistance than standard RPTFE. Good for steam service -50°F to 450°F.
A proprietary highly filled polymer seat. Offers abrasion resistance of metal with significantly higher pressure and temperature than RTFE. Temperature -50°F to 470°F.
For service with severe flashing, hydraulic shock, high temperature or abrasive media. Typically we hard face a stainless steel seat with Stellite then lap the ball to the seat for tight shut-off. Depending on the valve and trim we can achieve temperatures in excess of °F for metal seated ball valves.
Triad&#;s high performance seat. Offers better creep resistance, lower coefficient of friction than that of PTFE, ideal for semi-conductor, hi-purity service.
75% PTFE +20% Glass Fiber +5% Graphite, good for temperatures from -50°F to 450°F, this material offers a wide temperature range with better life than RPTFE.
This material is very rigid, suitable for high pressure up to psi dependant on valve size and temperature range of -50°F to 180°F.
Best suited for high temperature and pressure service, suitable for tobacco and nuclear service. Temperature -70°F to 550°F.
Ultra-high molecular weight polyethylene, ideal for use in low-level radiation service, this material also meets the requirements of the tobacco industry where PTFE is prohibited and it offers an excellent resistance to abrasive media. Temperature -70°F to 200°F.
Produces the rigidity of Delrin or Nylon in a high pressure valve but provides for smooth lower operating torques.
As a manufacturer of high performance and engineered ball valves, we are often asked about what industry standards affect ball valve products and what should be referenced when specifying and ordering. The answer to that question is not nearly as straightforward as with the gate, globe, and check valves that have historically been the primary go-to valves in refining. With the more common &#;rising stem&#; valve types, standards such as API 600, API 602, API 603, etc. have taken a lot of the guesswork out because much of the design and sealing methods are well defined. However, as ball valves become more prevalent due to better sealing and reduced emissions, reliance on standards alone is not sufficient. Assurance that the installed product meets process requirements relies on much more.
There are several standards that influence the design and performance of ball valves. At a basic level, ASME B16.34, ASME 16.10 and others govern the dimensions and wall thickness (among other things) of most all valves used in the refining and chemical industries. Standards like API 641 (emissions for quarter-turn valves), API 607 (fire testing for both &#;soft&#; and metal seated quarter-turn valves), and API 608 (requirements for metal ball valves generally up to NPS 24 and class 600 rating) guide the industry.
However, none of these standards address the suitability of sealing materials for individual processes. Since these valves are typically used in applications where sealing is critical to the process, there are several open questions that must be addressed when specifying ball valves.
Guideline Considerations for &#;Soft Seated&#; Ball Valves
By at least a 10:1 ratio, &#;soft seated&#; ball valves dominate the refining and chemical markets. Although this is evolving as the costs of metal seated valves come down, soft seated ball valves will likely continue to be the most cost-effective solution in relatively clean services under 450ºF.
There are a wide array of options for seating material in these valves. The vast majority used in the refining and chemical industry are based on a form of Teflon &#; / PTFE. Apart from the base material, there are molecularly enhanced versions and compounds filled with glass, carbon fiber and/or graphite. One problem that exists in many specifications for these types of valves is the vague term &#;RPTFE&#; which (not so simply) indicates reinforced PTFE. Without information on the type of reinforcement, this can be misleading. For example, if a request is made for RPTFE in a plant with HF Acid (which dissolves glass) and a valve with glass-filled PTFE is installed, the results will be very undesirable.
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In addition, manufacturers offer seat and seal materials like PEEK, Nylon, PCTFE, etc. for specific process requirements. All have certain properties that, when combined with specific seat designs, create allowable maximum (and minimum) temperature ranges and differential pressure.
It is well past the scope of this article to provide an application guide to all these seat types, but if you&#;re involved with selection or specification of these seat and seal materials, here are some guidelines to consider:
A very common question asked in the valve and automation industry is: what is considered a severe or critical service valve application? There are several groups, MSS in particular, that are working on a more objective standard to provide guidance on this question.
As it pertains to ball valves in the refining and chemical industry, the question becomes: when should a severe or critical service metal seated ball valve be considered? This is a rapidly expanding segment of the market that is widely misunderstood. The correct answer to this question is: when process requirements exist calling for ball valves that operate and seal in conditions outside the range of typical products, test protocols and industry standards. This can mean many things to many people, and one must take care to not simply throw money at a problem hoping it goes away.
In the petrochemical, chemical, and refining industries, some examples of applications where metal seats would be the preferred choice are:
It is important to understand that metal- to-metal sealing in ball valves is a misnomer. If uncoated metal balls and seats are in direct contact, they would be damaged due to galling when operated and would never seal well. In reality, it is the ball and seat coatings that provide the sealing and allow the valve to cycle without galling. These coatings are generally lapped for tight shut-off and must resist chemical and thermal attack from the process in which the valve is installed.
The key to reliability of &#;metal seated&#; valves in any process application is the selection of the right coating, and the lapping / grinding process to &#;mate&#; the sealing surfaces.
There is simply no &#;one size fits all&#; for &#;metal-to-metal&#; sealing. Coatings are extremely application dependent. There are literally hundreds of material options and combinations, although certain technologies are more common.
Some of the more standard coating options are:
All have their positives and negatives in terms of performance in given applications and cost. The Cobalt overlays (commonly referred to as Stellite&#;) and Chrome Plating are still widely used in ball valves, as well as other valve types.
The most common ball and seat coating in severe service is the HP-HVOF process in which the coating mechanically bonds to the substrate material. In this process, a robotically controlled &#;gun&#; creates high kinetic energy allowing the coatings to be applied in a compressive state. The mechanical bond created is > 12,000 PSI bond strength for carbides, 5,000 &#; 7,000 PSI for chrome oxide ceramic. Some downsides to this process are that even at the lowest porosity, there is still poor sealing on gas applications. In addition, any carbon content makes these coatings susceptible to oxidation.
In the spray & fused process, the ball and seat surfaces are coated with a relatively thick layer of hardening material, then the part is heated to &#;fuse&#; (similar to welding) the coating to the base material for the highest possible bond strength and lowest porosity. This process is best for small molecule gas and particles.
Finally, is the plasma coating process where the specialty coatings are brought to a very high temperature prior to being robotically applied to the metal. This again creates a good bond strength, and coupled with the ceramic-like materials applied, creates a very corrosion resistant surface.
Ball valves have been around for many years and represent a very large portion of our industry, but they still require attention to detail and an understanding of the applications in which they will be installed. While there is no such thing as &#;zero leakage&#; in valves, by clearly defining the process objectives and properly specifying these products, the greatest reliability can be achieved.
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About the Author
Barry Hoeffner, Director of Quarter Turn Products at Ladish Valves has over 30 years experience in the Chemical and Refining Industries. As a Chemical Engineer, Barry brings a unique perspective to the Flow Control space. His focus for the years in the Valve Industry has been in application engineering and development of severe service and engineered ball valves
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