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Article: Purchase a Qualified Valve for Your Application

Qualification testing is beneficial but should never be the sole basis for a purchasing decision.

 By Jason Jablonski, Emerson

Jason Jablonski, Director of Engineering for Fisher Rotary Valves at Emerson Automation Solutions, wrote an article in the November 2019 issue of Chemical Engineering Progress titled Purchase a Qualified Valve for Your Operation. He writes that qualification testing or certification of valves gives the purchaser a degree of assurance, though this may be a false sense of security unless many other factors are considered in the purchasing decision.

 The qualification process depends on the standard to which the valve is being qualified.  In certain cases, testing can be done at the manufacturing facility, though most specifications require that a third-party witness attend, observe and document the tests. 

The test facilities must have valve-specific equipment and test fixtures to perform the required analysis.

Qualification testing can be done at the valve manufacturer’s test facility, such as the flow test facility at Emerson in Marshalltown, Iowa. 

Specific test equipment includes bunker and hydrostatic pumps, heat tape and insulation, thermocouples, torque and force meters, fluid leak meters, and mass spectrometers for evaluating fugitive emissions.

Typical tests include hydrostatic shell tests, and mechanical and thermal cycling of the valve while an operator measures seat leakage, fugitive emissions, and required actuator output.  Pressure retaining components may undergo non-destructive evaluation and sectioning to ensure that material strength and chemistry are acceptable.  

Valve Specifications

Valve specifications establish a minimum set of performance criteria. Common valve industry standards include ASME B16.5 and B16.10, which guarantee that valves of the same pressure class and size will have the same mating connection and end-to-end dimension. This allows a user to source and install equivalent replacements without converting mating piping and fittings. Table 1 lists many of the relevant U.S. valve standards.

Qualification Testing Concerns

Jablonski says these common qualification testing issues must be considered: 

Limited sample size. Qualification testing is conducted on just a few valves but it’s used to qualify an entire platform of products, assuming relatively consistent design. 

Most testing is done on only one device or a small batch, with tolerances and material strengths falling within a narrow band and not necessarily reflective of the variability allowed in production. 

Limited testing conditions. Valves are rarely tested at flowing conditions, where fluid dynamics may severely affect required torques or forces to close a valve.

For example, even if performance is confirmed at ambient conditions in a clean environment, the valve could fail where erosive or corrosive fluids are present. 

Erosion damage on the outlet of a separator inlet control valve in a coal seam gas application. Erosion was caused by the valve being oversized and operating barely open, coupled with poor material selection unable to withstand erosion from entrained particles.

 Variation and consistency. Seemingly minor variables can impact the valve capabilities. 

Where possible, controls should be put in place to vet any product changes. Periodic qualification testing can account for changes in people, processes and tools over time, though this risk can also be mitigated by testing each order.  

Production Testing

Consider other criteria to complement a qualification certificate. Testing valves as they are produced gives insight into their performance, Jablonski says. 

This may include non-destructive performance testing, such as detecting seat leakage, measuring stroke times, hydrostatic pressure testing or obtaining a valve signature pot to ensure operation is as expected. Alternatively, destructive testing can help determine the drivetrain failure force. Mechanical or metallurgical testing can determine the pressure and material strength limits. 

Valve signature plot showing a valve operating properly. 

Although measurements of key part characteristics such as stem surface finish may be important, it is more telling to measure performance characteristics—such as valve torques, seat leak rates, and fugitive emissions—to identify variations in the assembly before they become a problem

Mechanical cycles or flow erosion/corrosion can wear down seals and increase leakage. 

Live-loaded packing uses springs to account for packing consolidation, extrusion and oxidation. These springs are either placed on each gland packing stud or on the springs surrounding the stem.

 

 

Packing selection is critical for leak free valve operation. This image depicts the cross section of a live-loaded, low fugitive emission PTFE packing in an eccentric plug quarter-turn valve. 

Fugitive emissions continue to be of growing concern in the chemical processing industries, with much work being done in refining and chemical industries to set acceptable limits and test criteria. Jablonski says confusion is common, but valve manufacturers can help answer common questions. 

Standards committees are regularly updating the standards and criteria. The number of standards, variety of qualification levels, and frequency of changes have caused confusion for valve manufacturers and users alike.

 

 A lab technician measures leakage from the packing of a rising stem valve.

 Pressure and Cavitation Testing

The ASME B16.34 standard includes requirements and guidelines for valve pressure and seat leakage testing. However, pressure tests under this standard and others only verify that the valve does not fail during the testing—they do not assure the valve will be safe in operation.

 Cavitation, flashing and noise control are important in applications with high pressure drops. Special valve trims can be used to control noise and cavitation by breaking up the flow into smaller flow streams and reducing the pressure over multiple stages.

   

Cavitation and flashing may damage valve components but can be controlled with special valve trims. 

Design

ASME B16.34, considered the grandfather of valve design specifications, includes pressure and temperature ratings for common materials and dimensions, with specific emphasis on the calculation of wall thickness in different areas of the valve body. Even this venerable standard can cause confusion, but valve manufacturers can provide clarification. 

Determining the correct diameter based on bore and end connection dimensions and calculating the minimum required wall thickness can be confusing 

Reputable valve suppliers provide valves with thicker walls than the B16.34 calculations require. Finite Element Analysis (FEA) is commonly performed to determine where additional material is needed

 

 

Finite Element Analysis is commonly performed to determine where additional material is needed on a valve body. 

Summary

Qualification testing benefits the purchaser and manufacturer but should never be the sole basis for a purchasing decision, Jablonski warns. 

 It is only part of the information to consider, and must be evaluated in conjunction with other factors. The valve manufacturer’s reputation, design details, analysis of boundary conditions, quality management system, experience, production testing and product support should all be considered together with qualification testing when making a purchasing decision.

2 Replies

  • Hello Mark,

    I hope all is going well with you.

    I was wondering if I could ask you what is the reason for 70 to 80

    Psig lockup pressure of Fisher 627HM regulator with 240-500 Psig

    spring range. Please inform me has to do with this high lockup

    pressure failure of above-mentioned over-pressure protection

    regulator.

    Best Regards,

    Milan

    On 11/20/19, mark.nymeyer wrote:

    > [http://www.emersonexchange365.com/]

    > Update from Emerson Exchange 365 [http://www.emersonexchange365.com/]

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    > mark.nymeyer [http://www.emersonexchange365.com/members/mark.nymeyer]

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    > Qualification testing is beneficial but should never be the sole basis for a

    > purchasing decision.

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    > By Jason Jablonski, Emerson

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    > Jason Jablonski, Director of Engineering for Fisher Rotary Valves at Emerson

    > Automation Solutions, wrote an article i

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  • In reply to Mohammad Milan :

    Hello Mohammad, Try posting as a new thread in the

    Actuators, Regulators & Other Final Control

    forum so someone more familiar with that product can help answer.