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Fluid conveyance · Stainless steel gate valves

TECHNICAL DATA SHEET

FT-TC-VAL-COMPUERTA-INOXB-001

Issue date: August 4, 2026 · Rev. 001

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Cast stainless steel gate valve ASTM A351 CF8M/CF8 — class 150 flanged ends, API 603 framework

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Cast stainless steel gate valve in ASTM A351 CF8M (cast equivalent of 316, with molybdenum) or CF8 (cast equivalent of 304, without molybdenum) from the TECTUL catalog, with class 150 flanged ends per ASME B16.5. Its design framework is API 603 — Corrosion-resistant, Bolted Bonnet Gate Valves — the API 600 version specifically intended for corrosion-resistant materials: the same solid-wedge, bolted-bonnet, OS&Y-stem concept, but with tolerances and scope adjusted to stainless castings instead of carbon steel. The class 150 working pressure in the austenitic material group of ASME B16.34 is 275 psig (19 bar) at 38 °C, practically the same as a class 150 carbon steel gate valve in this same series: the reason to choose stainless is corrosion resistance, not extra pressure.

SKU VT-valvula-compuerta-inoxidable-bridada · class 150 flanged stainless gate valve, 2″ to 12″

1. Technical specifications

Materials and construction

Pressure-temperature table — class 150, CF8M (B16.34 material group 2.2)

Values from Table 2-2.2 of ASME B16.34 for material group 2.2 (CF8M/316). Group 2.1 (CF8/304) starts from the same 38 °C anchor point (275 psig) but falls somewhat faster at high temperature due to the absence of molybdenum; at ambient and moderate process temperature (up to ≈200 °C) both groups behave practically identically in allowable pressure. Note that the stainless class 150 (275 psig) is slightly lower than the carbon steel WCB class 150 (285 psig at 38 °C, group 1.1): the class is the same, but the exact rating also depends on the material group, not just the class number.

Face-to-face dimensions — class 150 (ASME B16.10, gate pattern)

Identical to the carbon steel gate valve table in this family: ASME B16.10 sets the face-to-face by valve type and class, not by body material. Weight does change with material and is confirmed on quotation.

2. API 603 versus API 600: the standard built for stainless castings

Why a separate standard exists for stainless

API 600 was written around carbon and alloy refinery steel, with wall thicknesses and tolerances designed for those materials. When the industry began asking for the same construction — solid wedge, bolted bonnet, OS&Y stem — but in corrosion-resistant castings (austenitic stainless, duplex, nickel alloys), API published API 603 as an independent standard instead of forcing API 600's same thicknesses onto a different material: cast stainless steel has different casting behavior, repair-weldability and strength than carbon steel, and a dedicated standard allows adjusting wall tolerances and casting acceptance criteria to that material without diluting either standard's requirements.

What the two standards share and what sets them apart

In practice, specifying "API 603" on a stainless valve order is more precise than specifying "API 600 in stainless": the latter phrase describes the design but not the actual manufacturing standard that applies to the material, and can lead to a different interpretation of tolerances between suppliers.

3. Corrosion, sensitization and why stainless rather than bronze or iron

The reason is corrosion, not pressure

As shown in section 1, the class 150 rating in CF8M (275 psig at 38 °C) is practically the same as in carbon steel WCB (285 psig at 38 °C): the rating is set by the ASME B16.34 class and material group, not by a structural superiority of stainless steel. The real reason to move from bronze, cast iron or carbon steel to cast stainless steel is corrosion resistance in a service that attacks those materials:

Sensitization: the weak point of cast stainless steel

Austenitic stainless steel is not immune to everything. Between roughly 425 °C and 870 °C, the alloy's carbon precipitates as chromium carbides at the grain boundaries — a phenomenon known as sensitization — depleting chromium in the zone adjacent to the grain boundary and leaving it susceptible to intergranular corrosion in the presence of a corrosive medium. It is relevant mainly in the heat-affected zone of casting repair welds, not in ambient-temperature service. When the project requires repair welding or prolonged service in that temperature range, a low-carbon grade (CF3/CF3M, equivalent to 304L/316L) or a post-weld solution heat treatment should be specified, neither of which is included by default in this sheet.

Chloride stress corrosion cracking

Austenitic stainless steel, including CF8M, is susceptible to chloride stress corrosion cracking (SCC) in hot chlorides — typically above ≈60 °C, in the simultaneous presence of chlorides, mechanical stress (residual or applied) and dissolved oxygen. This combination appears in hot seawater, concentrated brines or condensates with residual chlorides. In that scenario, "switching to stainless" does not solve the problem: duplex or superaustenitic alloys are required, and the selection belongs to the project engineer.

Flange finish and gasket compatibility

This valve's class 150 flanges follow the standard finish of ASME B16.5: raised face with concentric or spiral serrated finish, within the standard's roughness range, suitable for reinforced fiber, flexible graphite or spiral-wound gaskets. When the gasket is soft (elastomer or unreinforced pure PTFE), a finer finish than the standard serrated one is advisable so the concentric grooves do not cut into the gasket material — confirmed with the flange and gasket manufacturer on quotation. The gasket material must also be chemically compatible with the process fluid, a criterion independent of face finish.

4. Frequently asked questions

How much pressure does the flanged stainless gate valve take?

275 psig (19 bar) at 38 °C in class 150, per ASME B16.34 material group 2.2 (CF8M). It falls to 235 psig at 93 °C and 80 psig at 427 °C. It is a figure practically identical to a class 150 carbon steel gate valve (285 psig): the class, not the metal, decides the pressure.

Does stainless steel take more pressure than carbon steel?

Not for being stainless. Both are class 150 and their ratings are nearly equal (275 psig versus 285 psig at 38 °C); the difference between the two materials is marginal in pressure and decisive in corrosion resistance. The reason to choose stainless is never extra pressure.

What is the difference between API 600 and API 603?

API 600 was written for carbon and alloy steel; API 603 is the equivalent standard for corrosion-resistant castings (stainless, duplex, special alloys), with wall thickness and casting tolerances adjusted to that material, in sizes 1/2″ to 24″ and classes 150 to 600. The construction concept — solid wedge, bolted bonnet, OS&Y — is the same in both.

Are CF8M and CF8 the same thing?

No. CF8M carries 2–3 % molybdenum and is the cast equivalent of 316; CF8 has no molybdenum and is the cast equivalent of 304. Molybdenum improves chloride pitting resistance. Both share practically the same pressure rating at moderate temperature; they differ in chemical resistance, not in pressure.

Does this valve work for hot seawater or concentrated brine?

Not without further evaluation. CF8M is susceptible to chloride stress corrosion cracking in hot chlorides above ≈60 °C. That scenario requires duplex or superaustenitic alloys, and the selection belongs to the project engineer.

Can I weld repairs on the body without risk?

With caution: the heat-affected zone of a repair weld can become sensitized (425–870 °C) and susceptible to intergranular corrosion. If repair welding or prolonged service in that range is anticipated, a low-carbon grade (CF3/CF3M) or post-weld heat treatment should be specified, neither included by default.

5. Application notes

6. Technical notice and limitation of liability