Flanges for US chemical plants
Chemical plants pick flange materials for the fluid, not the pressure: the wrong grade corrodes in months. Here is how the common grades compare, and which flange types keep cost down on alloy lines.
Chemical process piping in the US is built to ASME B31.3 and uses ASME B16.5 flanges whose material is chosen for the fluid: 304L and 316L stainless for most acids, caustics and solvents, 904L and duplex S32205 where chlorides or sulfuric acid attack 316L, super duplex S32750 for the most aggressive chloride service, and lap joint flanges with stub ends to keep alloy cost down. We supply all of these, check every stainless flange by PMI, and can supply them pickled and passivated to ASTM A380 and A967. Indian chemical and fertilizer makers we have supplied include FACT, Madras Fertilizers and DCM Shriram.
Where flanges are used in chemical processing
| System | Flange | Class and material |
|---|---|---|
| General acids, caustic and solvents | Weld neck or slip-on RF | 304L, 316L |
| Chloride-bearing streams, brines | Weld neck RF | Duplex S32205, super duplex S32750 |
| Sulfuric and phosphoric acid | Weld neck RF | 904L, 316L by concentration |
| Alloy lines where cost matters | Lap joint with stub end; carbon steel backing ring | Stub end in the line grade |
| Utilities: steam, cooling water, nitrogen | Weld neck and slip-on RF | A105, Class 150 and 300 |
| Sampling and instrument connections | Socket weld and threaded flanges, NPS 2 and below | 316L, Class 150 to 600 |
Choosing the grade
| Grade | UNS | Specification | Strength in corrosive service |
|---|---|---|---|
| F304L | S30403 | ASTM A182 | Nitric acid, caustic, most organics; low carbon for welded lines |
| F316L | S31603 | ASTM A182 | 2 to 3% molybdenum for better pitting resistance; the default for chemical plants |
| F321, F347 | S32100, S34700 | ASTM A182 | Stabilized grades for hot service |
| 904L | N08904 | ASTM A182 F904L | High nickel and molybdenum for sulfuric acid and chlorides |
| Duplex 2205 | S32205 | ASTM A182 F60 | Chloride stress corrosion resistance at about twice the yield strength of 316L |
| Super duplex 2507 | S32750 | ASTM A182 F53 | Seawater and hot chloride service |
Our duplex and super duplex flanges are qualified to NORSOK M-650, the manufacturer qualification that offshore and process operators use for these grades, by Gulf Lloyds. Duplex needs controlled forging and solution annealing to keep its phase balance, and the qualification covers both.
Lap joint flanges to save on alloy
On a lap joint, only the stub end touches the fluid, so the flange ring behind it can be carbon steel even on a 904L or super duplex line. The ring also turns freely, which makes bolt holes easy to line up on tanks and equipment. See lap joint flanges and stub ends.
Verification and finish
Every stainless and duplex flange is checked on our Bruker PMI analyzer and the result is recorded on the certificate. Intergranular corrosion testing to ASTM A262 Practice E and impact testing can be arranged through outside laboratories when your specification asks for them. Fabricators who passivate after welding can order flanges already pickled and passivated, so the final clean covers the welds only.
Ordering for a US project
Send your line list with the standard, type, size, class, bore or schedule, facing, material and quantity for each line, and we quote every line as specified. Every order ships from our works in Gujarat, India; we have no US office or warehouse. Each line is supplied to your line list, and ordering from India explains the documents, marking, packing and customs.
Frequently asked questions
Do you supply 904L flanges?
Yes, along with 321, 347, duplex S32205 and super duplex S32750, to ASME B16.5. Give the grade, type, size and class on the line list.
Can you supply stub ends with lap joint flanges?
Yes. Stub ends to MSS SP-43 or ASME B16.9 in the line grade, with carbon steel or stainless lap joint flanges.
Do you test for intergranular corrosion?
On request, to ASTM A262 Practice E, through an outside laboratory, with the result on the certificate.
Sources
- ASME B31.3, Process Piping
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24
- ASTM A182/A182M, Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
- NORSOK M-650, Qualification of Manufacturers of Special Materials
- ASTM A380 and ASTM A967, cleaning, descaling and passivation of stainless steel parts