Figure 3: The difference between a 6” CL1500 valve( left) and a 6” CL2500 valve( right) results in more than double the weight, a 40 +% increase in pipe takeout distance, and nearly double the initial capital cost( about USD 67,000 versus USD 116,000). π
STANDARDS
Figure 2: This ASME Standard CL1500 valve chart shows the maximum allowable pressure and temperature ratings of Fisher CL1500 valves made of different materials.
In addition to ASME Standard Class valves, there are also ASME Special Class, ASME Intermediate Class and ASME Special Intermediate Classes available. Each of those options are discussed below.
ASME Special Class pressure ratings
In the case of weld end valves, some valve manufacturers offer ASME Special Class ratings. The ASME Standard Class ratings assume a base level of material and casting quality, which results in relatively conservative pressure and temperature ratings. However, most manufacturers can perform NDE testing on a specific valve body, and based on these test results, the ASME Code allows the manufacturer to rate the valve at higher pressures at elevated temperatures, even though the base level of material and casting quality does not change. For example, one can compare the Standard Class CL1500 chart in Figure 2 with the Special Class CL1500 chart in Figure 4. At ambient temperatures, both the Standard Class and Special Class valves have the same pressure ratings. But at higher process temperatures, the Special Class pressure ratings elevate considerably. A Standard Class CL1500 WC9( carbon steel) valve is rated for 2245 PSI at 900 ° F. The Special Class CL1500 WC9 valve is rated for 3000 PSI at that same temperature. If Special Class pressure ratings exceed the process requirements, the user can pay a relatively small extra charge for NDE testing, and they can then use a Special Class CL1500 valve instead of the much larger and more expensive Standard Class CL2500 valve. This saves significant money on the valve purchase itself, as well as reducing valve weight, space requirements and overall installation costs. Sometimes the Special Class pressure rating is still not enough to meet the process needs. In this case the user can consider an ASME Intermediate Class valve.
ASME Intermediate Class pressure ratings
Certain weld end valve body designs incorporate valve wall thickness exceeding that required by code. In these cases, some manufacturers can certify these valves to a higher-pressure class rating than Standard Classes. The specific pressure rating will depend upon the valve itself, as well as the material of construction, and the resulting pressure class will usually fall between the Standard Class ratings. For instance, a Fisher HP series WC9 CL1500 valve could carry a CL2017 Intermediate rating. As Figure 5 shows, the pressure ratings at elevated temperatures may not be much higher than the Special Class CL1500 valve— in this case the Intermediate Class CL1500 rating at 900 ° F is 3020 PSI versus 3000 PSI for the Special Class valve. However, there is a significant difference at ambient temperatures. As the chart indicates, the Intermediate Class CL2017 valve is rated for 5045 PSI at ambient
Figure 3: The difference between a 6” CL1500 valve( left) and a 6” CL2500 valve( right) results in more than double the weight, a 40 +% increase in pipe takeout distance, and nearly double the initial capital cost( about USD 67,000 versus USD 116,000). π
www. valve-world. net Valve World June 2025
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