The standard specification for instrument valves, MSS SP-99-2016a – Instrument Valves, has been revised. This standard applies to small valves and manifold valves developed for and predominantly used in instrument, control, and sampling piping systems. It covers steel and alloy valves of nominal pipe size (NPS) 2 and smaller, with pressure ratings of 15,000 psi and lower at 100 °F.
While it is not limited to one valve design, the MSS SP-99-2016a – Instrument Valves standard can be used to specify needle valves, packless valves, ball valves, plug valves, check valves, and manifold valves. The standard prepares the different valve designs for use as instrument valves by detailing their design requirements, which are to be assessed through testing methods.
The first primary group of tests featured in MSS SP-99-2016a – Instrument Valves is that of qualification tests. These exist to qualify the valve designs through two specific tests: hydrostatic proof and burst tests. The proof test calls for each test valve to pass hydrostatic shell proof test with minimum requirements for fluid (such as water or hydraulic oil), temperature (within the range of 50 °F to 125 °F), pressure, time, and position.
The second qualification test, the burst test procedure, hydrostatically shell tests the test valve to failure by rupture. At the end of this test, the user should record the hydrostatic pressure at which rupture occurs. The valve should be the same as the one used for the proof tests.
These qualification tests allow for a determination of the pressure rating, in which the CWP rating shall be less than or equal to the pressure determined from the burst pressure as follows:
P ≤ 0.25 B Tm/Ta1
Where P = CWP Rating, B = the lowest burst test pressure recorded for three specimens tested, Ta = actual tensile strength of the test specimen, and Tm = specified minimum tensile strength of the material.
The second group of tests is comprised of acceptance testing, which calls for each production valve to pass a seat leakage test and a shell test. The standard test methods are to be conducted with a liquid or gas and should meet minimum requirements specific to the state of matter used for the process. The characteristics covered are identical to those of the qualification tests (fluid, temperature, pressure, time, and position).
As the result of these tests, users of MSS SP-99-2016a – Instrument Valves can determine essential qualities of the test valve, all of which should be visibly marked by the manufacturer. This should include, at least: manufacturer’s identification, flow direction, manufacturer’s model number, and material grade.
MSS SP-99-2016a – Instrument Valves was written and published by the Manufacturer’s Standardization Society of the Valve and Fittings Industry (MSS), an ANSI-accredited standards-developing organization. Any guideline for valve specification and marking not addressed by this standard can be found in other MSS standards.
MSS SP-99-2016a – Instrument Valves is now available on the ANSI Webstore.
1. Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. (MSS), MSS SP-99-2016 – Instrument Valves (Vienna: MSS, 2016), 5.