Valve trim: what 13Cr and a hard-faced seat mean
Valve trim is the set of internal parts that meet the fluid and make the seal: the closure member, the seating surfaces, the stem and the back seat. 13Cr is trade shorthand for the martensitic stainless family behind it, usually Type 410. A hard-faced seat is one carrying a harder alloy deposited onto its sealing surface.
In this memo09 details
What counts as valve trim?
Valve trim is the set of internal parts that meet the fluid and make the seal: the closure member, the seating surfaces, the stem that drives them and the back seat. The body and bonnet form the pressure envelope and are specified separately. Trim decides whether the valve shuts tight on commissioning and still shuts tight after repeated cycling.
Seating surfaces may be machined into the body or carried on separate seat rings. The terms themselves are standardised: MSS publishes MSS SP-96, Terminology for Valves, Fittings, and Their Related Components, which the standards distributor Nimonik records as defining the principal terms used for general purpose valves and fittings.
This memo covers metal seated trim on isolation and regulating valves; control valve trim characteristics are a separate subject. The body side is set out in valve body materials: WCB, LCB and CF8M.
What does 13Cr actually name?
13Cr is trade shorthand for the martensitic stainless steel family used for valve seating surfaces and stems, and it is not a designation any standards body publishes. The grade usually meant by it is Type 410, UNS S41000, a hardenable stainless that takes and holds a seating face.
The shorthand rounds up. North American Stainless, in its Long Products datasheet NAS 451, describes Type 410 as a "High Hardenability martensitic, 11.5 per cent chromium Stainless Steel", and its composition table gives chromium at 11.5 to 12.5 per cent. The 13 in 13Cr is a nickname, not a chemistry limit.
What earns the grade its place in trim is that it hardens. The NAS 451 datasheet states that Type 410 "can be hardened to Rockwell C 39 minimum by air cooling or oil quenching from 1750 - 1850°F".
Two suppliers reading 13Cr may quote two different steels. Send a trim line to our counter on +6012 944 3980 or through contact us.
When does a valve seat need hard facing?
Hard facing is a harder alloy deposited onto a valve’s seating surface, and a seat is hard faced when the duty attacks the seating band rather than merely closing on it. A valve that is only ever fully open or fully shut on a clean fluid asks little of its seat. One held part open, or passing grit, scale or fines, wears a narrow band of metal under high local velocity, and a harder surface there lasts longer.
Writing in Valve Magazine, Reza Karimzadeh, a senior HVAC and mechanical engineer at Aker Solutions, and Karan Sotoodeh, a senior valve engineer at Baker Hughes, note that "valve internals, such as seats and closures, are often at risk of erosion, abrasion, corrosion, galling and damage from cavitation". They define galling as "a form of wear caused by adhesion between two sliding surfaces", occurring where components of similar hardness slide over one another dry.
Hard facing answers that list by laying a harder alloy onto the seating surface. The same authors record that the material most often used for hardfacing valve internals is a cobalt alloy containing chromium, tungsten and carbon.
| Duty on the line | What the duty does to the seat | What to settle with the maker |
|---|---|---|
| Open or shut only, clean fluid | Little, the faces meet and part | Whether a hardened seating face alone suffices |
| Held part open, throttling | Wire drawing across a nearly closed gap | Hard facing on closure member and seat |
| Carrying grit, scale or fines | Erosion and abrasion of the seating band | Hard facing, with the duty stated in writing |
| Metal seated, cycled hot and often | Galling between faces of similar hardness | The pairing of the faces, not just their hardness |
| Sour service | The environment, not the duty | Materials qualified against the named standard |
Confirm the answer with the maker for the valve quoted; none of it is taken from a standard.
Stellite or a classification: what should a specification name?
A valve specification should name the AWS classification of a hard-facing deposit rather than a trade mark. Stellite, the name most often seen on a hard-facing line, is a registered trade mark rather than a specification. A classification describes the metal that is deposited, and that is what an order can name.
The Australian Government's trade mark register records STELLITE, trade mark 25942, as registered in Class 6 for cobalt chromium alloy, owned by Kennametal Inc. A trade mark identifies a proprietor; it binds nobody to a composition on your order. An AWS classification does bind a composition. The American Welding Society record for AWS A5.13/A5.13M:2024 states that "classification is based upon the chemical composition of the deposited weld metal except for tungsten carbide electrodes, where classification is based on the mesh range, quantity, and composition of the tungsten carbide granules". For a cobalt alloy the class describes the metal that ends up on the seat; for a tungsten carbide overlay it describes the granules.
The dealer Certilas catalogues a cobalt chromium covered electrode under "AWS A 5.13: E CoCr-A", lists its as-welded hardness as 42 HRc, and names steam valves and exhaust valves among its uses. A deposit's hardness depends on how it is applied and how many layers go down, so the maker's figure for the valve quoted is the one that counts.
Why is a trim number alone not an instruction?
A valve trim number is shorthand defined by a standard, so it means something only once the order names that standard and its edition. Numbers such as Trim 1, Trim 5, Trim 8 and Trim 12 circulate widely in online summaries that reproduce trim tables, one example being projectmaterials. A summary is a third-party restatement, not the standard, and we do not quote one as authority.
The standard behind the best known gate valve trim numbering is API 600. The record held by the standards distributor Normservis gives it as API STD 600, 14th Edition, May 2021, Steel Gate Valves, Flanged and Butt-welding Ends, Bolted Bonnets, and lists metallic seating surfaces among the features it sets requirements for. Which gate valve standard a spec means is unpacked in API 600 vs API 602.
State the trim number with its standard and edition, or state the materials outright. A number alone invites two suppliers to quote two different valves and both to believe they complied.
What limits a valve trim choice?
Two things override a preference for a particular valve trim: the service environment and the temperature. Both are properties of the line rather than choices a buyer makes, and both are settled before any conversation about which seating face is hardest.
In sour service the environment selects the materials. When a line names NACE MR0175 and ISO 15156, closure member, seats and stem must all comply, and that is a question of qualified materials and condition, not of which trim is hardest. What naming that standard commits a supplier to is set out in NACE MR0175 and sour service.
Temperature limits the grade more plainly. North American Stainless gives Type 410 scaling temperatures in air of 1400°F intermittent and 1250°F continuous. Those scaling temperatures are a property of the steel, not of the valve, whose own rating is carried by its class, as set out in what Class 150, 300 and 600 actually mean.
What should an enquiry say about trim?
A trim line on a valve enquiry is quotable when it states the duty and the materials rather than a nickname. The supplier can then price one valve instead of guessing between three, and the certification requirements follow from it. Five lines are usually enough:
- The duty: isolate, or regulate and sit part open.
- The fluid, with anything it carries: grit, scale, fines, condensate.
- The operating and design temperature.
- Trim materials by grade and specification, or a trim number together with the standard and its edition.
- Hard facing: required or not, and on which faces.
Add any environment standard the line is subject to, and say what certification you need: test reports and material certificates are ordered, not requested afterwards. Which certificate does what is in EN 10204 3.1 and 3.2 certificates, and what the test report shows in API 598 valve testing. The full sequence is in specifying industrial valves.
NF Teguh supplies gate, globe, ball, plug, butterfly and check valves from Subang Jaya. Send a trim line to +6012 944 3980 or use contact us. More memos are in the insights register.
What else do buyers ask about valve trim?
Can we order a stainless trim in a carbon steel body?
Yes. The body is chosen for the pressure envelope and the trim for the sealing duty, so they sit on separate lines of the enquiry and need not be the same metal. State both.
Does valve trim guidance apply to a soft seated valve?
Only partly. Trim reasoning about hardness and hard facing concerns metal seating. A valve with a polymer seat is selected instead on that seat material's temperature and chemical limits. Say on the enquiry which it is.
Can hard facing be added to a valve we already own?
Adding hard facing to an existing valve is a repair question, not a supply one. Put it to the valve's maker or to a repair shop qualified for welding on pressure parts. We supply new valves specified for the duty.
Is it enough to write "hard faced seat" on the order?
Writing "hard faced seat" alone is better than silence, but it leaves the alloy and the faces open. Name the AWS classification, say which faces are to be faced, and state the duty that made you ask.
Sources
Read 18 October 2026.
- North American Stainless, Long Products datasheet NAS 451 for Type 410: the description of the grade, the ASTM designation 410 and UNS number S41000, the chromium range, the Rockwell C 39 minimum hardenability statement, and the scaling temperatures in air.
- Valve Magazine, "Hardfacing for Valves: Materials and Processes", 29 April 2019, by Reza Karimzadeh and Karan Sotoodeh: the risks to valve internals, the definition of galling, and the material most often used for hardfacing valve internals.
- The American Welding Society record for AWS A5.13/A5.13M:2024: the title and the quoted sentence on what classification is based upon.
- The Australian Government's Australian Trade Mark Search, trade mark 25942: the STELLITE word mark, its registered status, Class 6 cobalt chromium alloy, and its owner.
- The dealer Certilas, datasheet for the covered electrode CEWELD E DUR 6U: the AWS A 5.13 classification E CoCr-A, the as-welded hardness, and the listed uses.
- The standards distributor Normservis, catalogue record for API STD 600-ed.14: the title, the 14th edition date of May 2021, and the gate valve features the standard sets requirements for.
- Nimonik, catalogue record for MSS SP-96-2017, Terminology for Valves, Fittings, and Their Related Components: the title, the April 2017 issue and the scope sentence. No definition from it is reproduced here.
- projectmaterials, "Valve Trim Numbers": cited only as an example of a third-party summary that reproduces trim tables. Nothing from its tables is used or endorsed here.
No trim table, trim number content, acceptance level, chemistry limit or clause from any standard is reproduced here, and the table above is our own wording. These designations are identifiers and publisher record facts only, and no NF Teguh stock, capability or certification claim attaches to them. Confirm every line against the maker's own documentation and the current edition. Your purchase order governs.
Related memos
Standards named above are published reference data. Confirm against the current edition; your purchase order governs. Questions: the counter.