Valve MAST (Maximum Allowable Stem Torque): Its Relevance and Use in Valve Automation

One of the most important criteria when performing calculations for sizing of automated and manually-operated valves is considering the valve’s MAST value. The MAST value is the Maximum Allowable Stem Torque, defined as the greatest torque to which a valve stem can be subjected to during operation without mechanical failure.

Historically, its relevance was somewhat reduced in the valve and actuation industry, especially when it came to actuator sizing. Even today, you may be hard-pressed to find it included in sizing procedures in any manufacturer’s standard catalogue since this information is usually considered proprietary to design. However, as assets age and failure history is established, this value’s importance and demand for accuracy have adopted a more influential role in actuator sizing today.

Failure to identify, select, and size inclusive of the MAST value usually results in a partial or full shearing of the valve stem causing anything from valve leakage to complete loss of control. In some cases, it is not necessarily shearing that occurs but rather deflection during operation. The cause of this deflection originates from the selected stem material being too soft to withstand the applied forces to the disc, ball, or plug. Unfortunately, this discrepancy yields a chronological accelerated wear of the sealing surfaces which ultimately gives way to premature leakage and accelerated valve failure. The valve, and its level of importance in the application, determine the severity of the failure’s outcome. It is important to understand that there is currently no regulation by API (American Petroleum Institute) that requires manufacturers to publish their MAST values or “raw” torque values, despite mutual agreement throughout the industry by valve experts and engineers that such information is essential to actuator sizing and lifetime valve performance.

“Raw” torque values refer to the valve torques that have not been inflated by a manufacturer’s internal safety factor (which is usually added to account for manufacturing tolerances). In most cases this all boils down to the repeatability of each manufacturer’s manufacturing process and various checkpoints for quality control. Most manufacturers have very predictable manufacturing tolerances; however, they elect to omit the safety factor from published torque data. This exclusion is the primary reason why MAST values are exceeded. Excessive torque at the stem when sizing actuators will create a need to consider changing stem material. Specifying a higher yield stem material will prevent deflection or in the worst-case complete valve failure due to sheering. There are many different factors that can affect stem material selection and design in valves. Whether butterfly valves, ball valves, or plug valves, the customer or EPC provides the application conditions and, in turn, the valve manufacturer or automation supplier recommends a product that meets the provided conditions. Factors that may affect stem material selection are pressure class, process media, environmental factors, and client classification requirements.

Since valve manufacturers and distributors usually stock only the most popular valves to reduce inventory costs and maintain a high level of turnover, valves with uncommon body, disc, and stem materials are typically only produced on a machine-to-order basis. Therefore, delivery of these products can range anywhere from 26-48 weeks with cost variances of four to five times the average. If the manufacturer does not state the provided values are raw, it is imperative for one to seek clarification for this added multiplier. In short, ask questions! Ensuring that this base torque value for the valve excludes a safety factor is of the utmost importance for the following reasons: 1) preventing a multiplication of safety factors and oversizing of the actuator and 2) forcing an unnecessary upgrade to the stem and disc material.

Some of the most common stem materials are listed below in increasing order in terms of MAST as well as cost impact:

  • 316/316L SS
  • 17-4 PH SS
  • Monel K-500
  • Inconel 718

It is crucial to consider safety factors from both the client-driven requirements and the built-in margin from the manufacturer. In doing so there will be instances where combinations of the above must be utilized. Even when MAST values have been identified, failure to confirm the manufacturer’s published numbers can drive up costs and lead times exponentially due to misinterpreted data. Correctly interpreting manufacturer’s data, identifying red flags, partnering with experienced automation groups, and having strong relationships with valve suppliers are all keys to ensuring that an automated valve assembly’s configuration is mechanically correct and cost-effective.

For more information or if you need assistance with valve automation contact:

Supreme Integrated Technologies

Houston:              281 822 5000


Blog Authors: Chris Sarro & Jacob Shoesmith


My Intern Experience at SIT

Our Campus Ambassador Program allows interns to be hired on for the summer and gain hands-on experience. Learn what it’s like to intern at Supreme Integrated Technology through Tyler Foreman’s perspective, who concluded this program last month.

“During my summer as an engineering intern at Supreme Integrated Technology I learned so many useful skills that has propelled me forward in both my education as well as preparation for my career. I worked on a wide variety of projects in the fast-paced atmosphere of the office including designing parts, drawings and assembly of a items for hydraulic power applications. After speaking with many of my peers back at the University of Louisiana at Lafayette who are also doing summer internships at different companies it really gave me a sense of the realization of just how valuable of an experience that Supreme Integrated Technology has given me.

I really didn’t know what to expect when I showed up for my first day of my internship because I have never experienced a summer internship before. I figured that I would be doing minor projects around the office, mostly just tedious tasks that the other engineers just didn’t feel like doing. I was also skeptical because I have had no experience in school learning about hydraulic and fluid power experience because it is not taught in our curriculum. But when I showed up, I felt as though I was being treated as a new hire, not a summer intern. I had so many questions when I first showed up and I was greeted with more answers and support that I could have possibly expected. I was included on all the meetings to learn how projects are reviewed step by step as the design process goes from start to finish. This allows the Mechanical Engineers to receive needed feedback from each other, being that these are custom hydraulic systems, every project that they receive could be completely different from the last. This allows for an incredible learning experience in an engineer’s career and having this level of support from the team you work with provides better engineers and a successful company. After the first meeting that I sat in on, I had so many questions regarding many of the symbols as well as terms that they were using because they were very unfamiliar to me. Everyone present has a prompt answer to each question that I had and made sure that I knew it before they were done explaining. After the meeting one of the engineers sat me down and proceeded to give me a Hydraulics 101 course on all the basics in order to familiarize myself with the work that they did. I was amazed by how knowledgeable he was and so thankful for his willingness to take an hour and a half out of his day to teach me everything from common symbols that are used in the schematic to common equations that are used in hydraulic calculations.

Being a student for most of my life I have not been able to get a lot “real world” experience when it came to the field of engineering. It was nice to see all the technical studies that I learned in school come to life in the work place. Sometimes as a student it feels like we are in a constant cycle of tedious concepts that we are forced to learn and memorize, which I find makes it difficult to determine what is important and what is applicable in the workplace. As I was working my internship this summer, I really enjoyed seeing these classes come to life in my work. One of the most rewarding parts of this job was seeing a project go from the design phase, to the calculation phase, then to go out into the shop to witness these ideas and design become physical projects. I felt such a sense of excitement when I attended the Campus Ambassador Program in Houston. While we were there meeting with all the different companies in EOHI and was able to ask questions regarding what each company does. When we were on the tour of Supreme Integrated Technology in Houston, they brought us into the shop to see all of the current projects we had going on. I was looking around and I saw a familiar item that was in an opened box. It was a pinion that the engineers in New Orleans had me design and make a model of. This was the first time that I had seen a physical item that I designed sitting on the floor in front of me. I will always remember that moment because that was the first time that I felt like a true engineer.

Overall, I have cherished my summer internship experience here at Supreme Integrated Technology. I learned so many useful skills and experience that has molded me into a more confident student as well as a hungry engineer eager to graduate in December so that I can start my career. From life lessons given to me by my mentors, technical knowledge, industry experience and what it is like to work day-to-day as a Mechanical Engineer. As a student so close to graduation, I began to question whether the major I chose was the right pick for me. After working this summer, I know now that there is no other place that I want to be. I have such a renewed passion for my career choice, and I am so thankful for Supreme Integrated Technology simply putting me to work so that I could realize that.”

We appreciate all the hard work and fresh ideas Tyler brought to our team of engineers. We wish him the best of luck with his future endeavors!  

Supreme Integrated Technology Supplies over 100 Jacking Systems Worldwide

Birth of an Industry

The phrase “necessity is the mother of invention” can be attributed to many of the innovations across the world throughout time.  It is expressly apparent in the birth of the self-elevating vessel (liftboat) market that is a staple in the offshore oil and gas and windfarm industries.  With its roots in south Louisiana, the liftboat market started with the need for vessels not subject to the impulses of wave action.  Elevating above the water, these vessels could minimize the vast amount of downtime waiting for Mother Nature by providing a safe and stable working platform for a multitude of operations.  Traditionally, the liftboat market predominantly serviced the offshore oil and gas industry, but over the last few years there has been a shift toward utilization in the installation of offshore windfarms.  With the US targeting the development and installation of utility-scale windfarms in the next few years, the birth of a whole new US windfarm industry may be on the horizon.

Jack-Up Barge M.B. 1
Mutawa Marine Works.
Year Built: 1995

History of Excellence

Supreme Integrated Technology (SIT) has been engrained in the liftboat industry as a premier system provider for jacking systems used to elevate the vessels.  Huber Inc., a predecessor of SIT, provided its first jacking system in the 1980s. After completion of the first vessel, Huber would go on to provide jacking systems in varying capacities for over 50 vessels, all manufactured in the US.  SIT, a company formed by former members of the Huber leadership team, in 2013 successfully acquired the assets of Huber, Inc. to secure the knowledge base and market presence that the team had built previously while at Huber.  In 2016, SIT and its sister company Hydraquip Custom Systems Inc. (HCSI) successfully completed a merger with the assets of HCSI coming under SIT to more effectively take advantage of the existing synergies between the two companies.  With the merger of SIT and HCSI, many of the international vessels using HCSI-provided jacking systems would now be assisted by SIT.  Jacking systems have been provided collectively by SIT and its predecessors in numerous volumes, with many of these vessels operating today in the oil and gas and wind energy markets.

Liftboat Jill
Montco Offshore
Year Built: 2014

US Market Presence

According to market research, as of June of 2015, there were around 309 liftboats built or modified in US shipyards.  Of those 309 vessels, SIT and its legacies had supplied jacking systems in varying capacities for over 90 of these vessels, nearly a 29% market share of the entire US-built fleet of liftboats!  In addition to the jacking systems, SIT has expanded the scope of supply by also providing several vessels with various  systems for steering, ballasting, propulsion, thrusters, and more.

International Market Presence

SIT also boasts a considerable market share of the international liftboat market.  SIT estimates that of the over 100 vessels that have SIT-provided or legacy jacking systems onboard, between 25% and 45% are currently in service outside of the US.  With these vessels operating in the waters of the US, Mexico, Middle East and Northern Africa, South Africa, Southeast Asia, Europe, and the North Sea, SIT is truly a global system provider.  SIT has even developed a network of equipment providers and service specialists to continue to allow SIT to provide the highest quality support for its systems in nearly everywhere in the world.  SIT is very excited to see what the future will bring for liftboats in both the offshore oil and gas industry and the offshore renewable resources industry.