Home Valve ComparisonsForged vs Cast Valve Body: Which Material Process is Better?

Valve Comparison Guide

Forged vs Cast Valve Body: Which Material Process is Better?

Compare forged and cast valve bodies: manufacturing process, porosity risk, pressure class, API 602 (forged) vs API 600 (cast), NACE suitability, cost, and size range.

Overview

Forged Steel Valve Body

A forged valve body is produced by working (pressing, hammering, or rolling) a steel billet at high temperature until the metal takes the shape of a valve body. The forging process aligns the metal grain structure along the direction of mechanical stress, eliminating casting porosity and producing a denser, more uniform microstructure than casting. Forged valves are covered by API 602 for gate, globe, and check valves in small bore sizes (NPS ¼" to NPS 4"). ASTM A105 is the most common material for carbon steel forged valve bodies.

NPS ¼"–NPS 4" (API 602) | Class 800–2500 | A105, A182 F316, A182 F11/F22 | SW, threaded, BW ends | API 602, ASME B16.34

Cast Steel Valve Body

A cast valve body is produced by pouring molten steel into a mould that defines the valve body shape. After solidification, the casting is heat-treated, machined, and inspected. Casting allows large, complex-shaped valve bodies to be produced economically — a DN600 Class 300 gate valve body with complex internal geometry would be impractical to forge but is routinely cast. ASTM A216 WCB is the most widely used material for cast carbon steel valve bodies. Cast valves are covered by API 600 for large bore gate valves and API 623 for globe valves.

NPS 2"–NPS 60" | Class 150–2500 | WCB, WCC, LCB, CF8M, WC9, WC6 | Flanged RF/RTJ | API 600, API 623, ASME B16.34

Pros & Cons

Forged Steel Valve Body

No porosity — forging eliminates the casting voids and shrinkage cavities that can occur during solidification of molten metal; forged bodies have a fully dense microstructure

Higher strength — forged grain structure is aligned and continuous; ultimate tensile strength and impact toughness are higher than cast equivalents of the same alloy composition

Better NACE MR0175 sour service compliance — forged A105 bodies achieve hardness control (HRC ≤22) more reliably than cast WCB bodies; forging process improves microstructure uniformity

Preferred for small bore (NPS ¼"–NPS 4") — small bore castings are difficult to produce without defects due to the small cross-section; forging is the practical solution for small bore

High pressure rating — forged bodies (Class 800, 1500, 2500) are standard for high-pressure small bore service; very high-pressure (Class 2500) large bore valves use forged bodies too

Non-destructive testing (NDT) is simpler — forged bodies have fewer internal defects to find; RT and UT examination is faster and more reliable

Limited to smaller sizes — forging large valve bodies (above NPS 4"–NPS 6") becomes very expensive; casting is more economical for larger sizes

Higher cost at medium and large bore — forging dies, high-temperature presses, and billet material make forged large-bore valve bodies significantly more expensive than castings

Socket weld or threaded end connections (API 602) — small bore forged valves typically use SW or threaded ends rather than flanged ends; flanged forged valves require forged flanges welded to the body

Not socket-weld compatible above NPS 2" in high-pressure service (ASME B31.3 restricts SW above certain pressure classes)

Complex alloy grades (WC9, P91) are harder to forge than to cast — high-alloy forged bodies are produced in smaller quantities and have longer lead times

Cast Steel Valve Body

Economical at large bore — casting is far cheaper than forging for bodies above NPS 4"–NPS 6"; most of the cost is in machining, which is the same for both

Complex shapes possible — casting allows integral flanges, complex internal geometry (multi-port bodies, Y-body globe valves) that would be impractical to forge

Wide size range — cast valve bodies are routinely produced from NPS 2" to NPS 60" (and larger for special applications)

Widely available — WCB cast valve bodies are produced by hundreds of foundries worldwide; maximum supply chain availability and shortest lead time

Higher-pressure classes at large bore — Class 150 through Class 2500 cast large-bore valves are available; very large bore Class 2500 flanged valves (e.g. main steam isolation) are cast

Lower cost for complex alloy grades at large bore — alloy steel (WC9, WC6) and stainless steel (CF8M) are economically castable in large sizes where forging would be prohibitively expensive

Porosity risk — molten metal shrinks as it solidifies; poorly designed or controlled casting processes produce voids (shrinkage porosity, gas porosity) inside the casting wall; may pass hydrostatic test but fail in service under cyclic load

Radiographic examination (RT) required — cast bodies must be radiographically examined (ASME Section V, API 598) to detect internal defects; forged bodies rarely require RT as they are inherently sound

Grain structure is random — cast microstructure has randomly oriented grains (no directional strengthening); impact toughness at low temperature is lower than equivalent forged material at the same composition

NACE MR0175 compliance is harder — achieving uniform hardness (HRC ≤22) across a large complex casting is more difficult than in a small forged body; multiple heat treatments may be required

Heavier at small bore — casting a small NPS ½" valve body is inefficient; casting minimums mean excess metal; forging is preferred at small bore

Forged Steel Valve Body vs Cast Steel Valve Body — Specification Comparison

Parameter	Forged Steel Valve Body	Cast Steel Valve Body
Manufacturing Process	Hot working (pressing, rolling, hammering) of solid billet — no molten metal	Pouring molten steel into a mould — solidification shrinkage creates porosity risk
Porosity	Zero porosity — solid worked metal; no voids or shrinkage cavities	Porosity possible if casting design or process is not well controlled — requires RT inspection
Grain Structure	Aligned with applied force — directionally strengthened; higher impact toughness	Random grain orientation — adequate strength but lower impact toughness than equivalent forged
Applicable Standard	API 602 (gate/globe/check, NPS ¼"–NPS 4"); API 6A (wellhead, forged)	API 600 (gate valves); API 623 (globe valves); API 594 (check valves)
Size Range	NPS ¼" to NPS 4" (typical API 602 scope); NPS 6"–NPS 14" for special high-pressure forged	NPS 2" to NPS 60" — casting is the dominant process for all large bore valves
Common Carbon Steel Grade	ASTM A105 (forged carbon steel — socket weld/threaded) or A350 LF2 (low temp)	ASTM A216 WCB (cast carbon steel — flanged/BW ends)
NACE MR0175 Sour Service	Easier hardness control — A105 forged achieves HRC ≤22 uniformly; preferred for small bore sour service	Harder hardness control — large WCB castings may require additional PWHT to achieve uniform HRC ≤22 across entire body
NDT Required	RT not typically required — forged bodies are inherently sound; UT and MT used for high-pressure forgings	RT required for body and cover per API 598 / customer specification — adds cost and time
Cost at NPS 2" Class 800	Lower — forging is most economical for small bore Class 800+ valves	Higher — casting a small bore Class 800 body is expensive and difficult; forging preferred
Cost at NPS 12" Class 300	Very high — forging a large complex gate valve body is extremely expensive	Lower — casting is the economical choice for all large bore valves

When to Use Each

Use Forged Steel Valve Body when:

Small bore (NPS ¼"–NPS 4") high-pressure process valves in Class 800, 1500, and 2500

Sour service (H₂S) valves under NACE MR0175 where forged A105 hardness control is critical

Instrument isolation valves, sample point valves, and gauge root valves in small bore NPS ¼"–NPS 1"

Compressor suction and discharge valves in high-pressure gas service

Any high-pressure small bore valve where casting porosity is an unacceptable risk

Use Cast Steel Valve Body when:

Large bore (NPS 6" and above) process plant isolation valves in Class 150 through Class 2500

All standard gate, globe, check, ball, and butterfly valves in the typical process plant size range (NPS 2"–NPS 24")

Complex body geometry: Y-pattern globe, multi-port bodies, valve bodies with integral bypass connections

High-alloy (WC9, WC6, CF8M) large-bore valves for steam, high-temperature process, and corrosive service

Any valve where casting economics are acceptable and NDE (RT/UT) is included in the QC plan

Decision Guide

The forged vs cast decision is primarily driven by valve size, pressure class, and bore: for small bore (NPS ¼" to NPS 4") high-pressure (Class 800, 1500, 2500) valves, forged bodies (API 602, ASTM A105) are the standard and economical choice — casting small bore bodies is impractical and more expensive. For medium bore (NPS 2"–NPS 6") at moderate pressure (Class 150–600), both forged and cast are available — cast bodies (WCB, API 600) are more commonly stocked and economical. For large bore (NPS 6" and above), cast bodies (API 600, API 623) are the only practical option — forging large complex valve bodies is prohibitively expensive and only used for special high-pressure applications (main steam isolation valves in Class 1500–2500). NACE MR0175 sour service at small bore (NPS ½"–NPS 2") strongly favours forged A105 — hardness control is more reliable in forged than cast bodies. For Class 2500 ultra-high-pressure service at any size, forged bodies (F91, F22) are preferred for the highest integrity applications.

Frequently Asked Questions

What is ASTM A105 and when is it specified for valves?

ASTM A105 is the ASTM standard specification for carbon steel forgings for piping components — the most common forged valve body material for gate, globe, ball, check, and plug valves in small bore sizes. A105 covers forgings intended for ambient-temperature to moderate-temperature service: maximum temperature approximately +450°C. The chemical composition is similar to ASTM A216 WCB (carbon steel), but A105 is a forging specification whereas WCB is a casting specification. Key properties: minimum yield strength 250 MPa (36 ksi), minimum tensile 485 MPa (70 ksi), maximum hardness 187 HBW (which is below the NACE MR0175 requirement of HRC ≤22 / HBW ≤237 — A105 forgings are inherently NACE-compliant for sour service when supplied in the normalised and tempered condition). A105 is specified for: (1) Socket weld (SW) and threaded gate, globe, and check valves in Class 800, 1500, and 2500 (the dominant specification — 'API 602 Class 800 A105 SW gate valve' is one of the most common industrial valve specifications); (2) Flanged small bore valves in Class 300 and above; (3) NACE-compliant sour service valves at small bore. The equivalent low-temperature forging grade is ASTM A350 LF2 — same forging process but impact-tested to −46°C for LNG and cryogenic service.

How is casting porosity detected and controlled in cast valve bodies?

Casting porosity in valve bodies is detected and controlled by: (1) Radiographic Testing (RT) — X-ray or gamma-ray examination of the cast body wall images the internal structure; voids appear as dark spots on the radiograph; API 598 requires RT of the body and bonnet per ASME Section V for most industrial valves. Acceptance criteria are per ASTM E446 for steel castings; (2) Ultrasonic Testing (UT) — used for thicker sections where RT penetration is limited; UT maps the internal grain structure and identifies large voids; (3) Magnetic Particle Testing (MT) — detects surface-breaking and near-surface defects in ferromagnetic castings; limited to surface/near-surface defects only; (4) Casting design control — the foundry must design gates, risers, and chills to direct solidification away from high-stress zones; simulation software (ProCAST, Magmasoft) is used to predict and eliminate shrinkage porosity before the first casting. Porosity control begins at the foundry design stage, not at the inspection stage — an RT-rejected casting has already wasted foundry time and customer schedule. Vajra sources cast valve bodies from approved foundries with documented casting process control, RT capability, and quality records to EN 10204 3.1 or 3.2.

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