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API 600 vs API 623: Globe and Gate Valve Standards
Gate valves are governed by API 600, while check valve design is covered in API 594. Prior to the release of the new standard API 623, it was common in the refining and petrochemical industries to reference the API 600 wall thicknesses for globe valves on specification sheets, even though API 600 only applied to gate valves. In fact, wall thickness was the only portion of API 600 requirements that could be applied to globe valves, as other factors such as stem diameters, packing sizes, and gasket styles were not relevant to globe valve design.
Challenges with Stem Diameters
One of the biggest concerns for the API 623 task force was the issue of stem diameters. Since the force required to close a globe valve is much greater than that of a gate valve, the stem diameters for globe valves tend to be much larger. Although each manufacturer had its own design requirements, there was no established industry standard for minimum stem diameters for globe valves. API 623 now sets that standard.
Globe Valve Stem Materials
Globe valves are often provided with stems made of austenitic stainless steels, such as 304ss, 316ss, and 347ss. These materials are not as strong as the standard 410 stainless-steel stem material. Therefore, when austenitic stems are specified, they must be larger in diameter to prevent bending or buckling. The new standard for globe valves addresses this concern by establishing minimum stem diameters that are compatible with austenitic stainless steels.
Minimum Wall Thickness for Globe Valves
Before API 623 was created, the minimum wall thickness for globe valves was based on recommendations from the American Society of Mechanical Engineers (ASME) B16.34 standard. The new standard for globe valves now mirrors the wall thickness specifications from API 600, which is greater than the thickness specified in ASME B16.34. This additional thickness produces a heavier valve pattern and enhances corrosion and erosion resistance. It also helps to prevent deflection in the bonnets of larger-diameter globe valves, a common issue that causes leakage due to the disc rising off the seat as the bonnet expands upward.
Applications of Heavy-Pattern Globe Valves
The new heavy-pattern globe valve is particularly useful in a variety of industries, including refineries, power generation, and chemical processing. Given the less-than-optimal casting quality in modern manufacturing, the extra wall thickness will be highly valued by many end users. The standard is applicable to a variety of body materials selected from ASME B16.34 Groups 1 and 2, which include plain carbon steels, stainless steels, and chrome-moly alloys. It does not apply to ductile or cast iron valves.
Seats and Seating Requirements
API 623 affects all aspects of globe valve design. As globe valves are primarily used for throttling and regulating flows, the flow rates from various manufacturers should align with the specifications for API 623 globe valves. Despite the convoluted and restrictive flow path of globe valves, which impacts fluid friction and flow rate, the standard now establishes minimum seat diameters to standardize one of the key variables in the flow rate equation.
Trim Materials for Globe Valves
Like other API valve standards, API 623 includes a table of trim materials. This trim chart is similar to the one found in API 600, and includes materials such as 410 stainless steel, 316 stainless steel, 304 stainless steel, Alloy 20, and others.
Gasket Materials
API 623 also provides several options for gaskets and gasket materials, including:
Metal ring joint
Spiral wound gasket with filler
Corrugated metal with graphite facings
Stop-Check Valves under API 623
One of the more popular valves found on the output side of steam boilers is the stop-check valve, which combines the operations of both a globe valve and a check valve in one valve body. Stop-check and angle valves are covered by API 623 and are included in this new standard. However, pressure-seal valves are not included in this standard.
