CF8, CF8M and CF3M are austenitic stainless casting grades commonly encountered in pressure-containing valve parts. WCB is a carbon-steel casting grade. Their names do not describe the trim, bolting, seat or every corrosion mechanism the valve will face.
01 / Material map
Start with the specification family and product form.
ASTM A351/A351M covers austenitic castings for pressure-containing parts such as valves, flanges and fittings. ASTM lists A351/A351M-24e1 as the current edition in its steel standards catalogue. Carbon-steel pressure castings follow a different specification family.
A cast grade should not be ordered only by a wrought label. CF8M is often discussed alongside wrought 316 because both include molybdenum-bearing austenitic chemistry, but the actual acceptance criteria belong to the cited casting specification.
| Grade route | Practical distinction | Do not infer |
|---|---|---|
| CF8 | Austenitic stainless casting route commonly compared with 304-family applications. | Universal chloride resistance or a complete valve material schedule. |
| CF8M | Molybdenum-bearing austenitic stainless casting route. | Suitability for every seawater, acid or high-temperature service. |
| CF3M | Low-carbon molybdenum-bearing austenitic stainless casting route. | That weld procedure, corrosion testing or all trim parts are automatically upgraded. |
| WCB | Carbon-steel casting route for pressure-containing parts. | Low-temperature toughness or corrosion resistance without additional requirements. |
02 / Service
Corrosion depends on the environment, not the grade name alone.
Fluid composition, concentration, temperature, oxygen, velocity, deposits, crevices and cleaning chemicals can alter performance. Chloride-bearing water is a good example: molybdenum can improve resistance in some conditions, but it does not make a valve immune to pitting, crevice corrosion or stress-corrosion cracking.
Carbon steel may be perfectly reasonable in a controlled non-corrosive service and unsuitable in another. Stainless steel can also fail when the service, fabrication condition or maintenance practice is wrong. Ask for the actual process chemistry and upset conditions.
03 / Components
Build a wetted-parts schedule before comparing quotations.
A body described as CF8M says nothing by itself about the stem, ball, disc, hinge pin, gland, seat retainer, spring or fasteners. Mixed materials may be deliberate, but they should be visible and reviewed for corrosion, galling, strength and galvanic interaction.
For each component, identify product form and material specification where critical. “316 trim” can hide whether a part is cast, wrought, hardfaced or coated, and whether the stated chemistry is backed by an original material certificate.
- Pressure boundaryBody, bonnet/cover, body connector and welded pressure parts.
- Pressure controllingBall/disc/wedge, stem/shaft, hinge pin and seat retainers.
- SealingSeats, packing, O-rings, gaskets and fire-safe secondary seals.
- FastenersBody joint, gland, cover and external bolting with coating where applicable.
- EvidenceMTC type, heat-number traceability, PMI and supplementary tests when ordered.
04 / Documents
The MTC and the valve serial number need a bridge.
A material certificate describes the material represented by that certificate. It does not prove that the material entered a particular valve. The manufacturing records must preserve heat identity through cutting, heat treatment, machining, subcontract work and assembly.
If PMI is specified, define components, method, acceptance and reporting. PMI can support alloy verification; it does not establish every mechanical property, heat-treatment condition or material origin.
05 / RFQ
Replace “SS316 valve” with a controlled material schedule.
State the body and bonnet casting specification and grade, trim materials, seat/seal system, bolting, any hardfacing, corrosion tests, certificate level, traceability scope and PMI requirement. Let suppliers list deviations part by part.
Where the process licensor or owner maintains an approved material selection diagram, use it. A supplier quotation should confirm compliance with that decision, not recreate corrosion engineering from a short fluid name.
Provide a component material schedule identifying specification, grade and product form for all pressure-containing, pressure-controlling and wetted parts. Submit original material certificates and the traceability record connecting required components to each valve serial number.
Sources / editorial control
Source basis
- ASTM steel standards catalogue. Lists ASTM A351/A351M-24e1 as the current austenitic casting specification.
- ASTM A351/A351M scope page. Official scope explains pressure-containing austenitic castings and purchaser responsibility for grade selection.
- EU Pressure Equipment Directive 2014/68/EU. Primary regulatory source for material identification and pressure-equipment requirements in EU scope.
Review limit: This comparison does not supply corrosion-rate data or approve a grade for a specific fluid. Use the current licensed material standard and the project corrosion/materials engineer’s service assessment.