API 600 vs API 603: Gate Valve Standards

API 600 and API 603 both cover flanged and butt-welding gate valves, but they address different body materials. API 600 covers carbon steel and low-alloy steel valves. API 603 covers corrosion-resistant (stainless steel and special alloy) gate valves. Understanding the distinction ensures the correct standard is referenced on datasheets and purchase orders.

Definition

API 600 (Bolted Bonnet Steel Gate Valves): covers cast steel gate valves with bolted or pressure-seal bonnets, in carbon steel (ASTM A216 WCB, WCC), low-alloy steel (ASTM A217 WC6, WC9, C5), and selected stainless grades. This is the primary gate valve standard for refinery, petrochemical, and power plant applications. Equivalent to ISO 10434.

API 603 (Corrosion-Resistant, Bolted Bonnet Gate Valves): covers cast corrosion-resistant alloy gate valves with bolted bonnets. Body materials include austenitic stainless steel (ASTM A351 CF8, CF8M, CF3, CF3M), duplex stainless steel, and nickel alloys. API 603 valves are typically thinner-walled than API 600 valves because stainless steels have higher allowable stresses at elevated temperatures.

When Used

API 600: carbon steel and alloy steel services; hydrocarbon processing, steam, high-temperature applications. Sizes 2” and above, Classes 150-2500. This is the default gate valve standard for most oil and gas applications.

API 603: corrosion-resistant services; chemical processing, offshore (chloride environments), pharmaceutical, food-grade, cryogenic, and any application requiring stainless steel or nickel alloy bodies. Sizes 1/2” to 24”, Classes 150-600 (typically).

Specs Table

Parameter	API 600	API 603
Full title	Bolted Bonnet Steel Gate Valves	Corrosion-Resistant, Bolted Bonnet Gate Valves
Body materials	A216 WCB/WCC, A217 WC6/WC9/C5/C12	A351 CF8/CF8M/CF3/CF3M, duplex, nickel alloys
Equivalent materials	Carbon steel, Cr-Mo low-alloy	304, 316, 304L, 316L SS, duplex, Monel, Hastelloy
Size range	2” and above	1/2” to 24” (common)
Pressure classes	150, 300, 600, 900, 1500, 2500	150, 300, 600 (up to 1500 for some sizes)
Wall thickness	Per ASME B16.34 (thicker for carbon steel)	Thinner than API 600 (higher allowable stress of SS)
Bonnet connection	Bolted or pressure-seal	Bolted
Trim	Standardized trim numbers	Corrosion-resistant trim
ISO equivalent	ISO 10434	ISO 15761
Pressure-temperature	Per ASME B16.34	Per ASME B16.34
NDE	RT or UT per ASME B16.34	RT or UT per ASME B16.34

Comparison

The two standards are complementary, not competing. API 600 is specified when the service conditions allow carbon steel or low-alloy steel bodies. API 603 is specified when corrosion resistance requires stainless steel or higher alloys.

Key technical differences:

• Wall thickness: API 603 valves can have thinner walls than API 600 for the same pressure class because austenitic stainless steels have higher allowable stresses at elevated temperatures per ASME B16.34.
• Weight: API 603 valves are lighter than equivalent API 600 valves due to thinner walls.
• Trim compatibility: API 603 valves use corrosion-resistant trim by default, while API 600 valves may use carbon steel or alloy trim depending on the trim number specified.
• Size range: API 603 starts at smaller sizes (1/2”) and generally covers a smaller maximum size than API 600.

Pro Tip

When specifying gate valves for stainless steel piping classes, always reference “API 603” on the datasheet, not “API 600 in stainless.” Although API 600 includes some stainless grades, API 603 is the purpose-built standard for corrosion-resistant gate valves and ensures the correct wall thickness, material testing, and documentation requirements.

For detailed information on gate valve types and design and valve body materials, see the linked guides.

Read the full guide to valve types