Valve World Americas Journal was happy to speak with Dustin Thompson, Engineering Supervisor of Franklin Valve, and John Brennan IV, Product Development Manager, to answer these low temperature valve questions.
By Brittani Schroeder
Applications Requiring Valves Constructed for Low Temperature
There are two different reasons an application might require a valve constructed for low temperatures; these being internal and external parameters. “Either your environment is very cold, or your processes are very cold. Sometimes, it can be both,” said John Brennan.
“The low temperature valves we work with are typically found where external temperatures dip as low as -50° Fahrenheit (F). For us, this means that most pipelines in the upper Northern hemisphere could require valves specified for low temperature applications,” said Dustin Thompson. “Other situations where low temperature valves are needed is in LNG and CNG pipelines; in this application the process is kept at cryogenic temperatures to keep the media in a liquid state.”
Meeting Parameters for Low Temperature Applications
To ensure that the valves will function correctly in a low temperature environment, certain parameters must be adhered to by the manufacturers. “When speaking about the applications our valves go into, the lowest temperature they experience is -50°F. For our products and applications, low temperature requirements are dictated within API 6D, which uses Charpy Impact Test acceptance criteria,” stated Dustin. “These requirements extend to the pressure containing components, and the bolting. When a user sees that Charpy Test report, they will be able to discern, based on the results, if the materials are compliant with process requirements.”
“For example, the standard bolting for our products is ASTM B7, and the low temperature would be L7. The material used for the production of L7 bolting undergoes additional testing to confirm the toughness of the material, and will be sufficient for the application,” explained John.
WHAT IS A CHARPY V-NOTCH TEST?
The Charpy V-Notch Test (also known as a Charpy Impact test) is a high strain-rate test that involves striking a standard notched specimen with a controlled weight pendulum swung from a set height.1
“The Charpy V-Notch Test is going to give you a toughness value. This value will essentially tell you how much energy that material can absorb at a specific temperature before it fractures,” explained Dustin. “So why is this important? For every metal, you are going to have a stress strain curve, which will dictate how much the metal will deform, and what type of deformation will occur at a given tensile load.
During the process of plastically deforming, the material also goes through strain hardening. This results in an increase in strength until it reaches its ultimate tensile strength, which is where the material would fail. Low temperatures have a direct impact on how much plastic deformation can be achieved prior to fracture. “So, essentially, you are doing this test to say, ‘At -50°F this material retains the ductility and toughness required to retain the published ultimate tensile strength that the application requires,’” Dustin continued.
Materials of Construction for Low Temperature Valves
When it comes to selecting the proper material of construction for a low temperature valve, it is best to look for a material with a high toughness or high ductility. “Toughness is a balance between ductility and strength. The more ductile the material is, the more it is going to be able to plastically deform before it ruptures,” said Dustin. For this reason, low carbon steels and austenitic stainless steels are a great choice when manufacturing valves for low temperature applications. “The austenitic stainless steels have inherently high ductility and a low carbon content.”
One of the greatest benefits of working with materials like austenitic stainless steels is the material’s corrosion resistance. Manufacturers can, however, run into difficulty with the machining process. “Machining a highly ductile material can be arduous due to their ability to deform past yield,” said Dustin.
“Another challenge that comes along with working with these materials is the cost. Often the high ductile materials, like austenitic stainless steels, are just more expensive than our standard materials,” John elaborated. “If you have a customer request a low temperature valve with an austenitic stainless steel body, that is a deviation from our off the shelf offering meaning the requested material is not kept in the regular inventory. That order will incur additional cost to get the appropriate materials, further increasing the cost.”
But where does this bump in cost come from? “Well, first, if you are looking for something with corrosion resistance, the cost is going to jump just from that requirement. Or the additional costs will come from the extra testing that needs to be done,” explained John. “As Dustin mentioned, the Charpy V-Notch Test needs to be performed, and that takes time and energy.”
Avoiding Failures with Proper Maintenance
When analyzing potential causes of failure in low temperature valves, Dustin and John believe it occurs in the style of a catastrophic fracture. “The most likely cause for a failure in low temperature applications is when materials are used that do not satisfy the Charpy acceptance criteria. The low temperatures will impact the material’s ability to distort prior to fracturing, thus reducing its ultimate strength,” said Dustin.
Another cause of failure could be that the materials of construction are not properly selected at the design phase for low temperature applications. Dustin continued, “If this happens, failure can occur when the metals contract or expand at different rates, causing components of a mechanism to no longer interact as designed for proper function. It is therefore imperative to look into the coefficient of thermal expansion when selecting materials.”
When speaking about failure in the valve materials, John stresses the importance of paying attention to the non-metal materials that can fail. “There is more than just metal in a valve. Our valves, for example, are soft-seated and have O-rings. You need to make sure your non-metal materials are rated for low temperatures too, because if the metal can get brittle, you better believe that rubber can get brittle. If it does get brittle, that is a guaranteed leak in the valve.”
As Dustin and John would say, “It is so important to ensure you are following the manufacturer’s IOM for scheduled maintenance and maintenance materials. If you are servicing a low temperature valve, ensure you are replacing components with the proper low temp rated replacement parts. If applicable, when regreasing components, ensure you are using grease rated for the operating temperatures.”
Important Considerations
When working with low temperature applications and valves, there are some important things to remember. “I think it is beneficial for both the end user and manufacturers to have a good understanding of what properties impact a material’s ability to perform in low temperatures, as well as the associated cost impact of obtaining and documenting these properties. In this way you can optimize spending while still ensuring safe operation,” stated Dustin.
“From the end user standpoint, I think it is really important to be aware of changes that can happen in various environments. If an end user is located where the weather forecast does not go below a standard valve’s operating range, they may not believe that they require a low temperature valve. This might not be necessarily true, and the end user needs to be aware of the different scenarios that can drive a valve to hit below -20°F,” explained John. “Factors like wind and moisture can have an effect on the temperature radiation. Many would be surprised by how much heat energy can be pulled away from a valve because of wind. So just being cognizant of that is crucial. If you can do that, your low temperature valve and application will perform well!”
REFERENCE
1. “What is a Charpy Impact Test?” Accessed at: https://www.twi-global.com/technical-knowledge/faqs/faq-what-is-charpy-testing#:~:text=The%20Charpy%20impact%20test%2C%20also,by%20the%20specimen%20during%20fracture.
ABOUT THE EXPERTS
Dustin Thompson is the Engineering Supervisor at Franklin Valve LP, Houston, TX. He Graduated Summa Cum Laude with a Bachelors in Mechanical Engineering Technology from the University of Houston, and has worked in valve design and manufacturing for Franklin for the past 6 years. His experience within those years includes dedicated product design, development of quality management processes, hands on research and development and project management.
John Brennan IV is the Product Development Manager at Franklin Valve, LP and has been working in product design and development at Franklin for the last 5 years. His focus has been on the improvement of existing product lines and development of new ones to address the needs of end users. He has a Bachelors in Mechanical Engineering from Auburn University and Masters in Business Administration from Rice University.