At the recent Valve Industry Knowledge Forum, Stan Hale, senior director of Supply Chain, MRC Global, reported on the status of International Society of Automation’s (ISA) TR96.05.01, and Carlos Davila, PE, product manager—Americas for Crane ChemPharma & Energy, gave updates on several standards from the American Society of Mechanical Engineers (ASME), American Petroleum Institute (API) and Manufacturer Standardization Society (MSS). Here are condensed reports based on their presentations.
PARTIAL STROKE TESTING
By Stan Hale
ISA’s working group responsible for ISA Technical Report (TR) 96.05.01, Partial Stroke Testing of Automated Valves, completed an update to the technical guidance provided in the original TR issued in 2008. The 2017 update is the result of a lengthy process that included industry-balanced input from end users, valve and actuator OEMs, process safety engineers, valve maintenance providers, engineering service companies and several consultants.
Much of the 2008 discussion of methods used to move or control a valve during a partial stroke test (PST) remains intact, and the industry has seen many products emerge since 2008 that ensure automated valves can be safely controlled as needed to facilitate a PST. The 2017 update introduces new PST concepts related to collection and analysis of data not included in the original 2008 version.
The most important new addition is the concept of margin. Margin is the difference between the torque or force required to move a valve to its intended position and the torque or force available from the actuator to make that happen. As long as actuator output capability remains greater than the torque or force required to operate the valve, the actuator will move the valve to its intended position. OEMs and automation suppliers ensure adequate margin is designed into new valves by applying safety factors during the automation engineering process.
However, practically all valve and automation OEMs list disclaimers at the end of their sizing worksheets that warn end users the calculated results are for new valves in clean service and the end user is responsible for specifying safety factors or adjustments needed to account for application specific margin degradation that occurs over time. Consistent with that valve OEM guidance and the margin discussion, the working group recognized “loss of margin” is a common failure mode that remains hidden during any testing process that does not employ measurements capable of indicating margin status.
After considerable debate, it became obvious the various PST implementations are not equal. Many end users do not make physical measurements during a PST, while others have implemented increasing levels of monitoring and analysis. This led to identification of four basic implementation levels or approaches to PST as defined below:
- Level 1−Partial stroke test without instrumentation
- Level 2−Partial stroke test with event timing
- Level 3−Partial stroke test with actuator-based instrumentation (e.g., control signal, pressure and position feedback)
- Level 4−Partial stroke test with external condition monitoring system that includes Level 3 parameters and incorporates process system and valve-based measurements (e.g., torque/thrust and acoustic leak detection)
The analyses conducted as the 2017 update was developed revealed proof test coverage increases significantly with each increasing level of implementation. During a Level 1 test, the valve is simply moved to an intermediate position and returned. Level 2 is often a feature of plant systems designed to automate the PST process that enables the user to trend the time required for the valve to travel between two known positions and detect changes that may indicate margin degradation.
A Level 3 approach is a built-in feature of certain valve controllers (e.g., position transmitters and positioners). The user looks for changes in the relationship between pressure and position supplied by the actuator instrumentation to assess changes in performance that indicate margin degradation.
Level 4 includes sensors and data acquisition devices installed on the valve and actuator but kept separate from the control system. This often includes torque or thrust gauges, pressure transducers, position transmitters and acoustic devices to detect leakage or flow when the valve is closed.
The working group also identified 48 different categories of failure causes and ranked them to understand which ones occur most often and which implementation level will be effective at detecting each. Guidance contained in the new technical report recommends end users perform a similar analysis and use either statistical data or a similar expert panel process to identify and rank the causes of failure for valves at their facilities.
After lengthy deliberation and analysis, the working group participants concluded performance measurements must be made during execution of the PST to make the process meaningful and provide the information on valve operability needed to properly support safety objectives. The working group remains active and plans to continue improving PST guidance as new data, experience or know-how emerges.
UPDATE ON ASME, API AND MSS STANDARDS
By Carlos Davila
ASME Standards B16.34 is the main standard for valves. A new edition was published in 2017 that has a three-year revision cycle in conjunction with ASME B16.5 and B16.47 (which cover flanges).
In the last revision, Paragraph 6.1.2 was approved. The proposal was to revise 6.1.2c and delete sub clause (1) and (2), which were revised in 2009. This caused some manufacturers of three-piece ball valves to substantially increase the wall thickness of the center body, resulting in additional weight for larger valves. After extensive discussion, a compromise was reached to approve both options.
The revisions also extended the scope of flanged and weld-end valve sizes from NPS 24 to NPS 60 to match B16.47 flanges.
A major review of needed material and pressure/temperature ratings corrections was conducted and included in the new edition.
The 2017 edition also allows use of ASTM International Editions other than those referenced in the standard (and with stated guidance and conformance). International Organization for Standards and MSS documents are referenced as guidance for construction of cryogenic bonnet valve extensions.
As far as B16 cases under B16.34, a case to use increased ceiling pressures for materials with high creep strength, F91, F92 and C12A, has been approved. Also, a B16 case, which adds unlisted materials not currently in B16.34, was approved by the board. This is more of an approval procedure than a case; it must be supplemented with actual material strength data and requires approval by B16 SC-N.
Several API standards are being revised or have just been issued recently including:
API 599, Metal Plug Valves–2013 (7th Edition)
A task force has been formed and is working to update to the next edition. The expiration was extended to 2020.
Proposed changes include increasing the size range from NPS 24 to NPS 36 and incorporating lift plug valves into the scope. The task force is also adding a requirement to comply with API 641, Fugitive Emission Testing. The first ballot for the next edition has been sent to the committee, and many comments were received. The task force will review the comments and prepare the next draft for balloting.
API 608, Ball Valves–2012 (5th Edition)
The task force is working to update the next edition. The expiration has been extended to 2019.
A section is being added to note double piston effect seats are outside the scope. An option for parallel threads for plugs is being added, and the task force also aims to address direct mounting of actuators.
A revision is being made to specify API-qualified packing must be used, and compliance with API 641 is under consideration.
API 621, Valve Reconditioning–2010 (3rd edition)
This standard was set to expire in 2017 so the current edition was reaffirmed, but the task force continues to work through the many issues and will prepare a draft for balloting. The main point is whether the standard requires a refurbished valve to be better than the original valve for fugitive emissions.
API 622, Type Testing Valve Packings–2011 (2nd Edition)
The last draft received no negative comments and has now moved to publication. The one-eighth packing test is included: The leak rate was 500 ppm and now is 100 ppm. The revision also changed the high-temperature corrosion test; no packing adjustments are allowed during the test.
API 623, Globe Valves–2013 (1st Edition)
The task force is working through issues for the next edition. Among them is a question of whether disc guiding is required for all globe valves with no valve to be stem-guided only. Also, glands and gland flanges must be at least as corrosion resistant as the body. Wall thickness is to follow B16.34, Table 3 for Group 3 alloy valves.
A ballot was issued to the committee. Many comments were received, and the task force is working on developing the next draft for balloting.
API 624, Type Testing Rising Stem Valves for Fugitive Emissions
The task force is working toward the next edition. The scope of the standard is to increase to 42 inches. Additional valve sizes will require testing.
Leakage from the body joint will be considered a failure and full retesting is being considered for valve design changes when packing is changed from a previous qualified type, when spacers are added, or when material is changed in the packing chamber or the number of sealing rings changes.
Among standards under development are:
SP-44, Steel Pipeline Flanges was published in 2016. However, dimensional errors were discovered and an errata sheet published. The standard was reissued in 2017.
SP-155, 2018. A new SP was developed and published covering plastic-lined, ferrous metal valves.
SP-55, 2011. Visual Qualification for Steel Castings is being expanded to include iron castings.
A new SP for Large Diameter Slip-On and Lap-Joint Flanges is being evaluated.
Additionally, SP-134, Valves for Cryogenic Service and SP-144, Pressure Seal Bonnet Valves are under revision for their next editions.
In August 2017, Carlos Davila wrote an article for VALVE Magazine called “An Update on U.S. Valve-Related Standards” that gave a fuller version of standards changes made up to that point. Go to www.valvemagazine.com.