API 602 vs ASME B16.34

API 602 and ASME B16.34 are complementary standards that govern forged steel valves, but they operate at different levels. ASME B16.34 is the base standard that defines pressure-temperature ratings, materials, wall thicknesses, and testing requirements for all flanged, threaded, and welding-end valves. API 602 is a product-specific standard that adds requirements for compact forged steel gate, globe, and check valves, referencing B16.34 for pressure ratings and material groups.

Comparison Table

Feature	API 602	ASME B16.34
Type	Product standard (specific valve types)	Base standard (all valve types)
Scope	Compact forged steel gate, globe, and check valves	All flanged, threaded, and welding-end valves
Size range	NPS 1/4 to NPS 4 (DN 8 to DN 100)	All sizes
Pressure classes	150, 300, 600, 800, 1500, 2500	150, 300, 600, 900, 1500, 2500, 4500
Pressure-temperature ratings	References ASME B16.34 tables	Defines the P-T rating tables
Minimum wall thickness	References ASME B16.34	Defines minimum wall calculations
Body material	Per B16.34 material groups (A105, A182, A350)	Defines all material groups
End connections	Flanged, SW, threaded, BW	Flanged, threaded, BW
Bonnet design	Bolted, welded, seal-welded, threaded (union)	Not specified (product standard defines)
Class 800	Defined (unique to API 602)	Not included
Stem design	Rising stem, non-rising stem	Not specified
Testing	API 598 (shell + closure)	Section 8 (shell + closure)
Extended body	Available for cryogenic/high-temp	Not addressed

Key Differences

Hierarchy: ASME B16.34 is the foundational standard that all valve product standards reference for pressure-temperature ratings and material qualifications. API 602 sits on top of B16.34, adding design details specific to small forged valves (gate, globe, check) that B16.34 does not address.

Class 800: API 602 uniquely defines a Class 800 pressure rating for socket-weld and threaded end valves. This class does not exist in B16.34 and provides a practical intermediate rating between Class 600 and Class 1500 for small-bore piping systems.

Valve-specific requirements: API 602 specifies bonnet types (bolted, welded, union), stem sealing (packing, bellows), backseat requirements, and handwheel operation that B16.34 does not cover. B16.34 provides only the pressure boundary (body, bonnet, end connections) requirements.

Testing: API 602 references API 598 for production testing, which defines specific test pressures and durations. B16.34 Section 8 also defines test requirements; when both apply, the more stringent requirement governs.

Common Mistake

Specifying ASME B16.34 alone for a forged gate valve. B16.34 defines pressure ratings and wall thicknesses but does not specify internal design features (gate type, stem, packing, bonnet). A complete specification requires both the product standard (API 602 for forged gate/globe/check) and the base standard (B16.34 for ratings). The valve data sheet must reference both.

Relationship Between Standards

Valve Type	Product Standard	Base Standard
Forged gate, globe, check (small-bore)	API 602	ASME B16.34
Cast gate valve (large-bore)	API 600	ASME B16.34
Ball valve	API 608 / API 6D	ASME B16.34
Butterfly valve	API 609	ASME B16.34
Plug valve	API 599	ASME B16.34

All valve product standards reference B16.34 for pressure-temperature ratings and material groups. The mill test certificate must confirm the body material meets both the product standard and B16.34 requirements.

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