STANDARDS
testing can then be used to qualify for the Special Class rating as well. The net result is a valve that has pressure and temperature ratings higher than the Standard, Special and Intermediate ratings. While the cost for an Intermediate Special Class valve is higher than either the Special or Intermediate Classes, the ability to use this option can yield enormous savings, particularly for large valve body sizes.
Savings
Here are a few examples that illustrate the potential savings that can be achieved by taking advantage of the Special, Intermediate and Intermediate Special Class ratings. Note that these savings are only for the valve cost, and do not take into account additional savings realised by using these smaller and lighter valves.
• An application requires a 2” WC9 carbon steel valve at 1000 ° F and 1428 PSIG.
° A Standard Class CL2500 valve would typically be required for this situation costing about $ 20,000.
° An Intermediate Class CL1694 valve would also work, costing about $ 14,000.
° Therefore, an Intermediate Class valve saves about $ 6, 000.
• An application requires a 6” WC9 carbon steel valve at 1000 ° F
and 1570 PSIG.
° A Standard Class CL2500 valve would typically be required for this situation costing about $ 93,000.
° An Intermediate Class CL1876 valve would also work, costing about $ 59,000.
° Each Intermediate Class valve saves about $ 34, 000.
• An application requires a 6” WC9 carbon steel valve at 1000 ° F
and 2030 PSIG.
° A Standard Class CL2500 valve would be required for this situation costing about $ 93,000.
° A Special Intermediate Class CL1876 valve would also work, costing about $ 59,000 + about $ 16,000 for additional NDE
testing and certification.
° Each Special Intermediate Class valve saves about $ 18, 000.
• As previously mentioned, the savings escalate quickly with larger
valves or special alloys. An application required a 16” x 12” Valve in C12A martensitic stainless steel suitable for 1085 ° F and 655 PSIG.
° Fisher had three options: quote an existing 16X12 2500 # design, design a completely new 900 # valve to meet the
requirements, or see if our existing 600 # design had any extra minimum wall thickness that would allow us to intermediate rate it, which it did.
• The existing Standard Class CL2500 valve, cost about $ 510,000.
• There was insufficient lead time to design a new CL900 valve.
• An Intermediate Class CL688 valve would also work, costing about $ 217,000. Large sizes like this are typically in a valve manufacturer’ s portfolio, and were in this case, but they may not be available in all sizes
The Intermediate Class valve saves about $ 293, 000.
°
Conclusion
When specifying weld end valves at elevated pressures and temperatures, end users would be wise to consult their valve vendor about ASME approved Special Class, Intermediate Class and Special Intermediate Class options. As indicated by the examples above, there are certain situations where these alternative class ratings can safely meet the process design conditions, while saving significant cost in the initial valve purchase price, as well as generating additional cost reductions from the decreased weight and size of the valves themselves. Figures all courtesy of Emerson
www. valve-world. net