What are 304 stainless steel flanges?

304 is an austenitic stainless steel made up of roughly 18% chromium and 8% nickel, which is why it’s often called 18/8 stainless. It’s one of the most widely used stainless grades, and a flange in this grade is the usual starting point when you need a stainless pipe connection.

A flange is the disc-shaped fitting that lets you bolt two lengths of pipe together, or bolt a pipe to a valve, pump or vessel. Because it’s bolted rather than permanently joined, the connection can be opened again for cleaning, inspection or repair.

We hold them to EN1092-1 and ANSI B16.5. If you need more corrosion resistance, our 316 stainless steel flanges are the step-up grade.

Which 304 flange ranges do we hold?

Below you’ll find our 304 flanges, sorted by standard:

ANSI B16.5 flanges: American-pattern flanges at 150LB and 300LB, in weld neck, slip-on, blind and threaded forms. ANSI stands for the American National Standards Institute.

BS10 flanges: British Standard 10 flanges in Tables D and E, ideal for replacing flanges on older British pipework.

EN1092-1 flanges: European flanges sized by DN (nominal diameter) and rated by PN (nominal pressure).

Reduced thickness flanges: thinner, flat-faced flanges for hygienic and metric pipework, drilled to EN1092-1 PN16 or ANSI B16.5 150LB.

All four ranges are made in 304 stainless steel. If you’re not sure which one matches your pipework, tell us the size and standard and we’ll point you to the right one.

What does A182 F304/L mean?

It looks like code, but each part has a meaning. A182 is the ASTM specification for forged or rolled alloy and stainless steel pipe flanges, forged fittings and valves. The F shows the flange is forged, and 304 is the grade.

The L stands for the low carbon version of the grade. Low carbon grades are widely used where flanges will be welded, because they reduce the risk of corrosion problems in the welded area.

Where are 304 flanges used?

304 suits a broad range of everyday stainless duties, such as from water and general process lines, where the media aren’t particularly aggressive. It’s a sensible default when the environment is clean, dry or only mildly corrosive. Stainless steel is widely chosen for pipework, and the benefits of stainless steel fittings apply equally to flanges.

Flanges are used wherever a joint needs to be taken apart, so you’ll find them on pump connections, valve connections, tank outlets and the ends of pipe runs. Which flange type you need depends on the duty, pressure, temperature and how the joint is made.

What are the limits of 304?

304 is a good all-rounder, but it isn’t the best choice everywhere. Where chlorides, salts or harsh cleaning chemicals are present, 316 is usually the safer specification because it contains molybdenum, which improves resistance to pitting.

Our 316 stainless steel flanges are the next step up, and the difference between 304 and 316 steel is worth understanding before you order. If you’re unsure which grade your environment needs, tell us about the duty and we’ll advise.

How do you choose the right 304 flange?

Work through these questions in order:

1. Which standard does your pipework follow?
We hold EN1092-1 flanges, ANSI B16.5 flanges and BS10 flange tables. Check how your existing flanges are sized, because DN and PN point to EN1092-1 while NPS and class point to ANSI B16.5.

2. Which flange type do you need?
RFSO flanges (raised face slip-on) are the economical option for lower pressure lines, and RFBL flanges (raised face blind) close off the end of a line.

3. Is your tube sized by outside diameter?
For hygienic and metric tube, RFSO bored O/D flanges are bored to suit outside diameter pipe.

4. Is the grade right?
Look for F304/L in the product name to see which flanges are in this grade.

5. What are you bolting it to?
Match the standard, rating and face of the mating flange, as a flange has to fit the one it joins.

What are the common ordering mistakes?

The most common mistake is mixing standards. EN1092-1 and ANSI B16.5 flanges use different sizing and drilling, so don’t assume they’re interchangeable. The second is mismatching the face, because a flange has to suit the face of the flange it’s joined to.

It’s also worth checking the grade across the whole system. Where you can, match the flange grade to the pipe and fittings, and ask your engineer if you’re deliberately mixing grades.

What should you tell us when you enquire?

The quickest way to get the right 304 flange is to start with the size and the standard. Please tell us:

1. The pipe size, either as a DN or NPS size or as the tube’s outside diameter.

2. Whether your pipework follows EN1092-1, ANSI B16.5 or BS10.

3. The rating you need, such as PN16 or 150LB.

4. The flange type and face, for example a raised face slip-on or a blind flange.

It also helps if you tell us how many you need and what the flange will be connected to. If you’re matching an existing flange, a photo or the markings on it will usually tell us the rest, so we can confirm the grade and specification with you before you order.

Frequently asked questions

What does A182 F304/L mean on a flange?

A182 is the ASTM specification for forged or rolled alloy and stainless steel pipe flanges, forged fittings and valves. The F shows the flange is forged, 304 is the grade and the L indicates the low carbon version, which is widely used where flanges will be welded.

What is the difference between 304 and 316 flanges?

The main difference is molybdenum. 316 contains around 2% molybdenum, which improves resistance to pitting where chlorides are present, so it’s usually the safer choice for coastal, marine and chemical duties. 304 suits milder, everyday duties.

Which standards do your 304 flanges follow?

We hold flanges to EN1092-1, ANSI B16.5 and BS10 standards. Look for F304/L in the product name to see which are in the 304 grade, such as our ANSI B16.5 weld neck, slip-on and blind flanges.

Contact Anglo Stainless for more information

As a major UK stockholder and supplier of stainless steel flanges and pipe fittings, we can supply the matching fittings too, from butt weld fittings to hygienic fittings. For help choosing the right 304 flange, please contact us and speak to a member of our team.