Reference 12th September 2026

What Do the Markings on a Ball Valve Body Mean?

Key Takeaway

The letters cast into a valve body are a specification, not a description. MSS SP-25 sets out what has to be there: manufacturer, rating, material, size, and where the purchase specification calls for them, melt designation and trim identification. The large pressure number is the one most often misread. WOG and CWP are cold, non-shock ratings, and a valve marked 1000 WOG is not rated for 1000 psi of steam, which carries its own mark and a much lower figure. The marks are also raised rather than stamped for a reason that has nothing to do with legibility: a sharp die impression in a pressure boundary is a notch, which is why API 6D permits marking on the body only by casting or by a low-stress die with a rounded V or dot face. And two of the things a buyer most wants to know, whether the body is really the alloy it claims and whether this particular valve was tested, are not in the marks at all.

What a standard actually requires

Most of what appears on a valve body is there because a marking standard puts it there. MSS SP-25, the standard marking system for valves, fittings, flanges and unions, lists the elements below. Two of them are conditional, so two valves can both meet the standard while carrying a different amount of text.

Element	What it looks like	When it is required
Manufacturer's name or trademark	A name, an abbreviation or a logo	In every case
Rating designation	1000 WOG, 600 CWP, CL150	In every case
Material designation	CF8M, CF8, WCB	In every case
Size designation	1/2, DN15	In every case
Melt designation	A heat or melt number	Only as the specification requires
Valve trim identification	A trim code	Valves only, and only when required

The standard is about content rather than method. Marks may be cast, forged, stamped, electro-etched, vibro-etched, laser-etched or otherwise made integral with the product, which is why the same information appears as raised letters on one valve and as an etched tag on another.

Reading the pressure mark

The large number is a pressure in psi, and the letters after it decide what that pressure applies to. Three abbreviations account for nearly everything found on a small ball valve.

Mark	Stands for	The pressure it states
WOG	Water, Oil, Gas	Non-shock rating at ambient temperature
CWP	Cold Working Pressure	Rating at temperatures up to 100 °F (38 °C)
WSP or SWP	Working Steam Pressure	Maximum steam pressure at the valve's highest temperature rating
CL, Class	ASME pressure class	A class, not a psi figure; the pressure varies with material and temperature

WOG and CWP describe the same idea and CWP is the more current of the two, but WOG still appears on new castings because patterns are long-lived and because buyers recognise it. Reading a valve marked both 1000 WOG and 150 WSP as though the first figure covered steam is the error that follows.

Reading the material mark

Cast valve bodies carry an ASTM casting grade, which is a different designation from the wrought grade a drawing usually specifies. CF8M and 316 describe the same family and are not the same specification, which matters when a drawing calls for one and a body is marked with the other.

Cast mark	ASTM spec	Wrought counterpart	Carbon	Molybdenum
CF8	A351	Type 304	0.08% max	0.50% max
CF8M	A351	Type 316	0.08% max	2.0 to 3.0%
CF3M	A351	Type 316L	0.03% max	2.0 to 3.0%
WCB	A216	Carbon steel	0.30% max	Not specified

The letters are readable rather than arbitrary. C means the alloy is intended for corrosion service, the digit is the maximum carbon in hundredths of a percent, and M means molybdenum has been added to the base alloy. Read that way, CF3M is the same alloy as CF8M at a lower carbon ceiling, and the family stops needing a lookup table.

Why the body marks are raised and the tag marks are not

A cast body carries its marks in relief. That is a consequence of how it was made: the lettering is cut into the pattern, so every casting off that pattern comes out with the same raised text, and the marks exist before the metal is poured. Changing them means changing tooling.

The reason they are not simply stamped afterwards is structural. A conventional die impression is a sharp-bottomed notch, and a notch in a pressure boundary is a stress concentrator. API 6D handles this explicitly, requiring that marking on the body, closure, end connector and bonnet be done either by casting or with a low-stress die-stamp of the rounded V or dot face type. The same logic is why serial numbers, heat numbers and test data usually appear on a tag or nameplate instead of being driven into the wall of the valve.

What is cast is fixed at the pattern. What varies from casting to casting, the heat number above all, has to live somewhere that can change per unit. A valve that arrives with no tag has lost the only part of its identity that was specific to it.

Which standard governs which mark

Marking is set by one standard, the valve itself by another, and the pressure figure by a third. A specification that cites only one of them leaves the other two to the supplier.

Standard	Covers	What it decides about the marks
MSS SP-25	Marking system for valves, fittings, flanges and unions	Which elements must appear and by what methods
MSS SP-110	Ball valves with threaded, socket welding, solder joint, grooved and flared ends	The design and rating behind the figure that is marked
ASME B16.34	Valves, flanged, threaded and welded end	Minimum wall thickness, permitted materials, pressure-temperature ratings from Class 150 to 4500
API 6D	Pipeline and piping valves	That body marking be cast or applied with a low-stress die
MSS SP-55	Quality standard for steel castings for valves	Not marking, but the surface the marks are cast into

The number most often misread

A body marked 1000 WOG tells a reader that the valve is rated to 1000 psi for water, oil and gas, non-shock, at ambient temperature. Every qualifier in that sentence is doing work, and none of them is on the casting.

Non-shock excludes water hammer and rapid closure. Ambient means the figure falls as temperature rises, and the body does not say by how much, because derating comes from a pressure-temperature table for the material rather than from the mark. Water, oil and gas is a list that does not include steam. A valve marked 1000 WOG and 150 WSP is stating two different duties, and the larger number is the one that does not apply to the steam line it might be fitted to.

The practical consequence is that the marking is a starting point for a check, not the end of one. The figure tells you which pressure-temperature table to open.

What the markings cannot tell you

Three questions a buyer usually has are outside what any body marking can answer, and knowing which they are saves asking the casting for something it does not hold.

Whether the alloy is what the mark says. CF8M and CF8 are cast from different heats and carry different marks, but the mark is applied by the pattern, not by an analysis of the metal that filled it. Confirming the grade means a material certificate and, on a finished body, a positive material identification reading.
Which heat it came from. Melt designation is marked only where the purchase specification calls for it. Where traceability matters it has to be specified, and it usually ends up on a tag rather than in relief.
Whether this valve was tested. Nothing in a cast mark records a shell or seat test. That lives in documentation, and documentation is per order rather than per pattern.

Seat and seal material is a fourth. Trim identification is required by MSS SP-25 for valves only when required, so a body with no trim mark is not defective, it simply was not ordered with one.

Checking a valve against its markings

Six things can be settled with the valve in hand and a drawing next to it.

Read the size mark against the end connection you actually need, since a size mark describes the nominal bore and not the thread form.
Read the rating letters before the number, because 1000 WOG and 150 WSP on the same body are two ratings and not a range.
Take the material mark as a cast grade and translate it to the wrought grade the drawing uses, rather than assuming CF8M and 316 are interchangeable designations.
Look for a tag. Heat number, serial number and test data are per unit and will not be in the casting.
Check that body marks are raised or applied with a rounded die, since a sharp stamp in the pressure wall is a defect rather than a marking method.
Open the pressure-temperature table for the marked material at the temperature the line runs at, because the marked figure is an ambient figure.

What this does not settle

Marking practice varies by product standard and by market. A valve built to API 608 for petroleum service, one built to MSS SP-110 for general threaded service and one built to a water industry approval will carry overlapping but not identical marks, and the absence of a mark on one does not imply a deficiency against another.

Approval marks are a separate category. A certification body's mark on a body or tag is governed by that body's own scheme rather than by MSS SP-25, and what it covers is a question for the listing rather than for the casting.

The pressure figures quoted here are read as they appear on typical small ball valves. They are examples of how the marks are structured and not ratings for any particular product.

Frequently Asked Questions

What is the difference between WOG and CWP on a ball valve?

They express the same idea. WOG stands for water, oil and gas and states a non-shock rating at ambient temperature. CWP stands for cold working pressure and states the rating at temperatures up to 100 degrees F. CWP is the more current mark and WOG still appears on new castings, partly because patterns are long-lived and partly because buyers recognise it.

Can a valve marked 1000 WOG be used on steam?

Not on the strength of that mark. Water, oil and gas is a list that does not include steam, and steam duty is stated separately as WSP or SWP, which is a much lower figure on the same body. A valve carrying both marks is stating two duties, and the steam duty is the smaller one.

Why is CF8M marked on the body instead of 316?

Because the body is a casting and CF8M is the casting grade under ASTM A351, while 316 is the wrought designation under a different specification. They describe the same family and are not the same specification. Under A351 the molybdenum in CF8M runs 2.0 to 3.0 per cent against 0.50 per cent maximum in CF8, which is the element that separates the two grades.

Why are the marks raised rather than stamped into the body?

Raised lettering is cut into the pattern, so it comes out of the mould with the casting and adds metal rather than removing it. This is also why putting a customer brand on a cast body is a tooling decision rather than a finishing one. A conventional die impression is a sharp-bottomed notch and a notch in a pressure boundary concentrates stress. API 6D allows body marking only by casting or with a low-stress die of the rounded V or dot face type, which is also why heat and serial numbers generally appear on a tag.

Is a valve with no heat number on the body non-compliant?

No. MSS SP-25 lists melt designation as required by the specification rather than in every case, and the same applies to trim identification for valves. Where traceability to a heat matters it is a purchase requirement, and it is usually satisfied on a tag and in the material certificate rather than in the casting.

Published by LINS Valve Industrial Co., Ltd., Taichung, Taiwan. Last Updated: 2026-09-12

Referenced standards: MSS SP-25 (standard marking system for valves, fittings, flanges and unions), MSS SP-110 (ball valves, threaded, socket welding, solder joint, grooved and flared ends), ASME B16.34 (valves, flanged, threaded and welding end), API 6D (pipeline and piping valves, marking method on the pressure boundary), MSS SP-55 (quality standard for steel castings for valves), ASTM A351 and ASTM A216 (casting grades).

Marking elements are listed as the marking standard sets them out. Individual product standards and certification schemes add their own marks, so a body may legitimately carry more than the list above. Pressure figures are used as examples of how a mark is structured and are not ratings for any particular product; the rating that applies in service comes from the pressure-temperature table for the marked material at the service temperature.