Valve trim refers to the internal parts of a valve that come in contact with the process fluid. For gate valves: seat rings, disc (wedge), backseat, and stem. For globe valves: seat ring, disc, backseat, and stem. The trim number (1 through 18) specifies the exact material combination for these parts. Trim selection directly affects the valve's corrosion resistance, erosion resistance, temperature capability, and service life.

What is the most common valve trim?

Trim 1 (410 SS / 13% Chrome) is the most common and economical trim. The seat, disc, backseat, and stem are all AISI 410 stainless steel. It provides good general-purpose corrosion resistance and is suitable for steam, water, oil, and gas services at temperatures up to 400°C. Trim 1 is the default trim for most WCB (carbon steel) body valves.

When should I use Stellite trim (Trim 5)?

Stellite (cobalt-chromium alloy) trim (Trim 5) should be used for: high-pressure drop applications causing erosion, frequent cycling (high-wear service), superheated steam, abrasive media, and services requiring tight shutoff after many cycles. Stellite is hard-faced (750 BHN minimum) onto the seating surfaces, providing exceptional wear and erosion resistance. It is significantly more expensive than Trim 1 but essential for severe service.

What trim should I use for seawater or corrosive service?

For corrosive services: Trim 8 (Monel) for seawater, brine, and alkaline solutions. Trim 10 (316 SS) for general corrosive chemicals. Trim 12 (Monel with hardfaced seats) for corrosive + erosive combined service. Trim 14 (Alloy 20) for sulfuric acid and other severely corrosive chemicals. For extremely corrosive environments, consider exotic trim materials like Inconel, Hastelloy, or titanium on special order.

Valve Trim Numbers Explained: Trim 1 to 18 Material Guide

February 11, 2026 7 min read Valve Materials

When specifying industrial valves, the trim number tells you exactly what materials are used for the internal sealing components — seat, disc, backseat, and stem. Selecting the right trim is critical: it determines the valve's corrosion resistance, erosion resistance, temperature capability, and service life. This guide covers all 18 standard trim numbers with their material combinations, sourced from manufacturer catalogue data.

What is "Trim"? Valve trim = the internal parts that contact the process fluid. For gate valves: seat rings, wedge/disc, backseat bush, and stem. For globe valves: seat ring, disc/plug, backseat, and stem. The trim number specifies the exact material combination for all these parts.

Standard Trim Chart (Trim 1–18)

The following table shows the standard trim material combinations per API 600 / BS 1414:

Trim #	Seat	Disc	Backseat	Stem	Notes
1	410	410	410	410	Standard — most common
2	Hard 410	410	304	410	Hardened seat
3	Hardfaced 410	Stellite	310	347	Seat 750 BHN min.
4	Hardfaced 410	Stellite	Hard 410	Alloy 20	Seat 750 BHN min.
5	Stellite	Stellite	Stellite	410	Full Stellite — severe service
5A	Stellite	Ni-Cr	Ni-Cr	304	Nickel-Chrome variant
6	Cu-Ni	Cu-Ni	Cu-Ni	316	Copper-Nickel service
7	Hard 410	Hard 410	Hard 410	410	All hardened 410
8	Monel	Monel	Monel	Monel	Seawater, alkaline
8A	Stellite	Stellite	Stellite	316	Stellite + SS stem
9	Ni-Cr	Ni-Cr	410	410	Nickel-Chrome
10	316	316	316	316	All 316 SS — corrosive
11	Monel	Monel	Monel	Monel	Monel hardfaced
12	Stellite	Stellite	316	316	Monel + hardfaced seats
13	Alloy 20	Alloy 20	Alloy 20	Alloy 20	Sulfuric acid service
14	Stellite	Stellite	Alloy 20	Alloy 20	Alloy 20 hardfaced
15	Hardfaced 304	Stellite	304	304	304 SS hardfaced
16	Hardfaced 316	Stellite	316	316	316 SS hardfaced
17	Hardfaced 347	Stellite	410	347	347 SS hardfaced
18	Hardfaced Alloy 20	Stellite	Alloy 20	Alloy 20	Alloy 20 hardfaced

Trim Selection Guide by Service

General Service (Steam, Water, Oil, Gas)

Trim 1 — the default and most economical choice. AISI 410 (13% Chrome stainless steel) provides adequate corrosion resistance for general utility services. Suitable up to 400°C.

High-Pressure Drop / Erosive Service

Trim 5 (full Stellite) — cobalt-chromium alloy hardfacing provides exceptional hardness (750 BHN minimum) and erosion resistance. Essential for: superheated steam, high-velocity flow, frequent cycling, abrasive media, and services requiring tight shutoff after thousands of cycles.

Seawater / Alkaline Service

Trim 8 (all Monel) — Monel (Nickel-Copper alloy) provides excellent resistance to seawater, brine, alkaline solutions, and de-aerated hydrofluoric acid. Standard choice for marine and desalination applications.

Corrosive Chemical Service

Trim 10 (all 316 SS) — for general corrosive service where 410 SS is insufficient. Trim 13/14 (Alloy 20) — for sulfuric acid and other severely corrosive chemicals. Alloy 20 contains ~20% Cr, 35% Ni, and 2–3% Mo with copper addition.

Combined Corrosion + Erosion

Trim 12, 16, or 18 — these combine a corrosion-resistant base material (Monel, 316 SS, or Alloy 20) with Stellite hardfacing on the seating surfaces. Use when both corrosion and erosion resistance are needed simultaneously.

Key Material Properties Reference

Material	Designation	Cr%	Ni%	Tensile (MPa)	Hardness (BHN)
WCB	A216 WCB	—	—	485	—
CF8	A351 CF8	18–21	8–11	485	—
CF8M	A351 CF8M	18–21	9–12	485	—
WC6	A217 WC6	1–1.5	—	485	—
WC9	A217 WC9	2–2.75	—	485	—
C5	A217 C5	4–6.5	—	620	—
410 SS	AISI 410	11.5–13.5	—	480	—
B7 Bolt	A193 B7	0.75–1.2	—	860	—
CN7M	Alloy 20	19–22	27–30.5	425	—

Conclusion

The trim number is one of the most important specifications when ordering industrial valves. It directly affects how well the valve will resist corrosion, erosion, and wear in your specific service conditions. When in doubt, start with Trim 1 for general service, upgrade to Trim 5 for erosive conditions, or consult with our engineering team for corrosive and exotic applications.

Need Help Selecting the Right Valve Trim?

Our engineering team can recommend the optimal trim for your service conditions. All standard trims (1–18) and exotic trims available.

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