Ball valves are versatile flow control devices suitable for extensive industrial applications. They are available in different sizes and designs, making them adaptable to diverse sanitary, petrochemical, and cryogenic applications.
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These valves control the flow of fluids through a hollow, pivoting ball that is either a full or reduced port. The dimensions of full port valves are equal to the internal diameters of the adjacent pipelines. The dimension of a reduced port (standard port) valve diameter is one pipe size less than the internal size of the adjacent pipe. For example, a 1” reduced port valve will actually use a ball with a ¾” port diameter.
Ball valves have several advantages over other industrial valves, with the most notable being:
They provide leak-tight seals.
They can open and close quickly.
They are more durable than most other industrial valves.
There are several ways to categorize valves. Each category or design determines the performance characteristics of the valve. The categories include:
Valve design based on ball movement: Floating and trunnion mounted
Port design: full port, standard, or V-port valve.
Body style: single body, split, top-entry, 3-piece or welded body.
There are a few questions that industrial engineers must ask before choosing ball valves. Finding answers to these questions guides the experts through the challenging valve selection process and helps select reliable ball valves that satisfy the requirements of the piping system. What are these questions?
1. What type of media will flow through the ball valve?
The first question that the engineers must address is the type of fluid that passes through the pipeline. Is it a liquid, gas or semi-solid (slurry)? Understanding the physical and chemical characteristics of the fluid helps analyze its behavior as it flows past the valve. Understanding the nature of the service fluid is vital for making decisions about valve materials, port designs and valve sizes. For example, when choosing a gas ball valve we must take into account its performance and reliability issues when working with combustible gases, like hydrocarbons, liquified natural gas or chemical vapors.
2. Which actuation methods will you use?
Pipeline designers must specify the type of valve actuation that will complement flow control operations. There are piping systems that require frequent valve operation and high precision levels. Other flow operations require a one-off activation of the ball valve. When choosing ball valves, the designer needs to quantify the frequency of valve operations. They also need to evaluate the energy requirements and complexity of actuation technologies. The available actuation methods for ball valves include:
Pneumatic actuation
Electric actuation
Manual operation
Hydraulic actuation
Evaluate additional actuation options like spring return or double-acting actuators as well. Understand the impact of add-ons like limit switches or pilot valves on the reliability of valves.
In processes that demand fast cycle times, pneumatic actuation for ball valves seems to be the most suitable choice. Engineers can install manually-operated ball valves in strategic pipe locations to facilitate pipeline isolation for maintenance or inspection. These low-cycle valves require operation a few times a year.
3. What are the temperature and pressure ratings of the pipeline?
Specifying the pressure and temperature conditions of the service fluid and the working environment is critical when selecting ball valves. The temperature ranges of the service fluid can alter the mechanical strength of the valve. If the temperature fluctuations are too high, the valve experiences non-uniform expansion and contraction that may lead to surface fractures with time.
Ball valves should sustain the pressure of the service fluid. Exceeding the designed pressure limits affects sealing quality and can cause premature wear. Select a ball valve with temperature and pressure ratings equal or higher to the ratings of the pipeline.
4. What are the estimated annual cycles?
The frequency of valve cycling affects the durability of a ball valve. Engineers should estimate annual operating cycles to determine the durability of different ball valves in the piping system. Other factors like maintenance and media abrasion affect the reliability of valves throughout their lifecycle.
The designers should estimate life expectancy of ball valves before choosing the actuation mechanism. If properly specified, ball valves can survive several tens of thousands of operations without failure. After understanding the cycling requirements, the engineers may settle on pneumatically actuated valves that guarantee better durability and reliability than electrically actuated counterparts.
5. How do you intend to use the ball valve?
While there are different types and brands of ball valves in the market, each has a definite application area. For instance, a steel ball valve for a chemical processing facility may not meet the specifications for use in a sanitary application. Ball valves provide shut-off for pipelines and can also provide directional control of fluids. When making selections for application-specific valves, the designer should understand whether:
The valve exclusively shuts off the flow.
The valve switches flow between sources.
Splits flow from one source to two different destinations (applies to 3-way ball valves).
Industrial applications operate under different pressure and temperature conditions. There are strict emission and leakage control requirements attached to diverse classes of ball valves. When selecting the ball valve, ensure that it meets minimum system requirements and regulatory specifications.
7. Which materials are used to manufacture the valve?
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Featured content:A Comprehensive Guide to Wafer Check ValvesThe type of valve materials comes down to the properties of the service fluid. When evaluating valve materials, engineers should verify:
The most common materials for ball valve bodies are brass, stainless steel, plastic, Monel, Inconel, Molybdenum, Chromium alloys, nickel alloys or copper. Severe service ball valves require materials with better strength and corrosion resistance values like Monel or Inconel.
When examining valve materials, the designers should pay attention to the composition of seal materials. Soft-seated ball valves may use rubber seals or PTFE seals. For extreme fluid service, the ball valves feature metal-to-metal seats.
Which testing and quality assurance procedures does your valve vendor use?
When working with vendors or manufacturers, the company should request information about testing protocols and quality assurance measures that they use. Testing procedures analyze the performances of different ball valves, leak and emission tests and pressure tests to ensure valves are safe for specific applications.
Do not purchase ball valves because they are the cheapest in the market. Take an extra step to evaluate the quality assurance criteria and standardization marks on the valve body or packaging. There is no point in purchasing ball valves in bulk, only for them to fail after a few working cycles.
8. What certifications should the valve have?
The application of ball valves spans different industries. In each sector, appointed organizations certify products to verify compliance with health and safety regulations. Depending on the type of application, ball valves and their actuators are subject to the following certifications:
ANSI certifications: Determines the pressure and temperature ratings for pipe flanges.
NEMA certifications: Sets the standards for the design of electrically actuated ball valves.
NSF certifications: Provide guidelines for selecting ball valves in food, beverage and drug production facilities.
Ball valves should have certifications relevant to the fluid applications you are running within the facility.
9. What are the maintenance requirements for ball valves?
Ball valves do not typically require a high volume of maintenance interventions. They have simple flow control mechanisms and are less likely to fail. However, that does not preempt the fact that industrial valves, at times, will require maintenance. When selecting valves, establish a plan for inspection and maintenance. Maintain a lean inventory of repair and replacement parts like seals for valves and consumables for actuators. Manual ball valves may require fewer maintenance interventions than actuated valves.
Conclusion
Selecting ball valves for different industrial applications is not a simple process. It requires a careful review of the technical specifications of the pipeline, a balanced selection of manufacturing materials, and research on the different valve industry codes and standards. By answering the above questions, engineers and pipeline designers can make informed decisions and select reliable ball valves that provide long-term service.
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Gilbert Welsford, a renowned valve industry expert and third-generation owner of FS Welsford Company, is the visionary behind ValveMan.com, a leading platform for valve-related products. Gilbert's profound understanding of fluid dynamics and precision engineering plays a pivotal role in designing and applying various valve types. Known for his collaborative approach and outstanding communication skills, he builds strong relationships across multiple sectors and consistently ensures successful project outcomes. Committed to innovation and excellence, Gilbert remains at the forefront of industry advancements, consistently delivering solutions that exceed expectations.
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.
- What is the pipe specification or process requirement?
This is almost always clearly stated and will help determine the body material of the valve.
- What is the valve process?
Valve “trim” material determined by valve process. Internal components must be compatible with the process to resist attack, and it must have the mechanical integrity to operate safely and reliably.
- What are the process conditions?
Because seat and seal material must be compatible with the process conditions, these must always be confirmed with the end user.
- What is the pressure / temperature?
Seat rating acceptability is determined by pressure & temperature.
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.
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:
- Always verify that the seat and seal materials are rated for the maximum or minimum design temperature, and the maximum differential pressure in the system where the valve is to be installed. All reputable manufacturers publish this information.
- If specifying reinforced PTFE seat material, note any material limitations or requirements around the ‘filler’.
- If automating, confirm the torque requirements of the specific seat material provided. This can vary greatly.
- Whenever possible, include the design temperatures and pressures in the specifications. This is especially important in cryogenic or other extreme conditions.
What is a Severe or Critical Service Application?
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.
Choose a Metal Seated Valve for These Applications
In the petrochemical, chemical, and refining industries, some examples of applications where metal seats would be the preferred choice are:
- Coking services
- High pressure hydrogen and gas isolation
- Catalyst handling
- Reactor isolation (manual and automated)
- ‘High cycle’ ball valves
- Heater isolation or…
- Places where reliable tight shut-off is important and soft seated’ valves will not function due to high temperature, pressure, wear, solids, etc. For example, ball valves that have a pressure rating Class 900 or above, or valves with a design temperature requirement exceeding 450ºF, could be considered a metal seat application.
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.
A Deep Dive into Modern Coating Technology
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:
- High Pressure-HVOF
- ‘Spray and Fuse’
- Cobalt Overlays
- Chrome Plating
- Surface treatments like Nitriding that are more of a surface hardening than a true coating.
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.
In Conclusion
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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