Flanges for US shipbuilding and offshore piping
Ships and offshore platforms run seawater through their piping, and seawater is hard on most steels. The flange materials on a marine line list reflect that.
Marine and offshore piping uses ASME B16.5 and B16.47 flanges, or the flange standard of the vessel's design rules, in carbon steel A105 and A350 LF2 for hydrocarbon and utility service, and duplex S32205 and super duplex S32750 for seawater, firewater and produced water. Our duplex and super duplex flanges are qualified to NORSOK M-650 by Gulf Lloyds, and Indian shipyards we have supplied include Cochin Shipyard, Hindustan Shipyard and GRSE.
Where flanges are used in shipbuilding and offshore
| System | Flange | Class and material |
|---|---|---|
| Seawater cooling and ballast | Weld neck or slip-on RF | Super duplex S32750, duplex S32205 |
| Firewater ring mains | Weld neck RF; blind flanges at spares | Duplex, super duplex |
| Produced water and topsides process | Weld neck RF and RTJ | Duplex, 316L, A105, LF2 |
| Fuel and lube oil | Weld neck or socket weld RF | A105, Class 150 to 300 |
| Hydraulic and instrument lines | Socket weld and threaded, small bore | 316L |
Why duplex for seawater
316L pits and suffers crevice corrosion in warm seawater, especially at gasketed joints, which is where flanges sit. Duplex S32205 and super duplex S32750 combine higher chromium, molybdenum and nitrogen with a two-phase structure that resists pitting, crevice corrosion and chloride stress corrosion cracking. Their pitting resistance equivalent numbers, about 35 for 2205 and over 40 for 2507, compare with about 24 for 316L.
| Grade | UNS | Specification | Typical service |
|---|---|---|---|
| A105 | K03504 | ASTM A105 | Fuel, lube oil, steam, dry systems |
| A350 LF2 | K03011 | ASTM A350 | Low temperature and cold-climate service |
| F316L | S31603 | ASTM A182 | Hydraulic, instrument and fresh water systems |
| Duplex 2205 | S32205 | ASTM A182 F60 | Seawater, firewater, produced water |
| Super duplex 2507 | S32750 | ASTM A182 F53 | Warm seawater and the most aggressive chloride service |
NORSOK M-650 qualification
Duplex and super duplex are easy to get wrong: poor forging or solution annealing leaves brittle phases that pass a hardness check but crack in service. NORSOK M-650 qualifies a manufacturer for each grade and process with impact, corrosion and microstructure tests, and many offshore operators accept duplex only from qualified makers. Our qualification, issued by Gulf Lloyds, covers duplex S32205 and super duplex S32750 to NORSOK M-630 material data sheets.
Classification and inspection
Ships and offshore units are built to the rules of their classification society, which may require surveyor-witnessed testing of piping components. Tell us the class society and the certificate type on the order, and we arrange the inspection and the EN 10204 3.2 certificate with the surveyor.
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
Are your duplex flanges qualified to NORSOK?
Yes. Our duplex S32205 and super duplex S32750 are qualified to NORSOK M-650 by Gulf Lloyds, covering NORSOK M-630 material data sheets D43, D44, D53 and D54.
Can a class surveyor witness the tests?
Yes. Name the classification society on the order and we arrange witnessed testing and EN 10204 3.2 certificates with the surveyor.
Which flange grade suits seawater?
Super duplex S32750 for warm seawater and critical lines, duplex S32205 for cooler or less critical service. 316L is prone to crevice corrosion at gasketed joints in seawater.
Sources
- NORSOK M-650, Qualification of Manufacturers of Special Materials
- NORSOK M-630, Material Data Sheets and Element Data Sheets for Piping
- ASTM A182/A182M, Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24