Product introduction
A marine exhaust gas bellows flange is the mating flange that clamps a stainless expansion joint to the engine exhaust outlet, turbocharger inlet or silencer inlet, absorbing thermal growth and hull flexure while keeping a gas-tight joint. It sees exhaust temperatures well above 400 C, thermal cycling on every start and stop, and acidic condensate plus seawater spray outside, so material and weld quality govern service life. Investment or resin sand casting produces the flange ring, bellows weld neck and any reinforcement or liner spigot in one piece, giving a clean, consistent weld preparation that a flame-cut plate flange cannot match. CNC turning and drilling then finish the gasket face, bolt circle, weld prep and bore.
Specifications
| Parameter | Specification |
|---|---|
| Materials | CF8M / 316L; duplex stainless 2205 (UNS S32205); super-duplex 2507 (UNS S32750); nickel-aluminium bronze C95800 / CuAl10Fe5Ni5 for seawater-cooled wet exhaust sections |
| Process | Investment casting or resin sand casting + CNC turning, facing, drilling and weld-prep machining |
| Dimensional tolerance | ISO 8062 CT6–CT8 (CT6 on gasket face, bore and weld prep, CT8 on outer rim) |
| Machining allowance | 2–4 mm on gasket face and bore; weld prep machined to final geometry |
| Surface finish | Ra 3.2 um as-cast; Ra 1.6 um on gasket face and bore; Ra 0.8 um on the bellows weld-prep land |
| NDT | 100% dye penetrant testing of all machined surfaces and weld prep; radiographic testing of the weld neck and flange-to-neck transition where specified; ultrasonic testing on sections above 25 mm |
| Pressure testing | Hydrostatic or pneumatic test of the assembled bellows and flange at 1.5 x design pressure; soap-bubble or helium leak test of the weld land on request |
| Heat treatment | Solution annealing and water quench for CF8M, 316L and duplex grades; sensitisation control and intergranular corrosion check where specified |
| Corrosion testing | Intergranular corrosion test to ASTM A262 Practice E on request; ferrite measurement on duplex welds |
| Size range | Nominal bore DN 80–DN 1200; flange outside diameter up to 1,600 mm |
| Documentation | EN 10204 3.1 or 3.2, dimensional report, NDT report, pressure test certificate |
Key features
- Cast flange with integral weld neck and machined bellows weld prep for a repeatable, full-penetration weld.
- Gasket face machined flat and concentric with the bore to hold a gas-tight joint through thermal cycling.
- CF8M / 316L for standard dry exhaust, duplex 2205 or super-duplex 2507 for high-chloride and wet exhaust duties.
- Solution annealed and quenched with controlled ferrite to resist sensitisation and pitting at high exhaust temperatures.
- Bolt circle drilled or reamed to your mating pipe flange standard (DIN, ANSI, JIS or yard standard).
- Optional internal liner spigot and insulation stand-off cast in to protect the bellows from direct flame impingement.
Applications
- Main and auxiliary diesel engine exhaust expansion joints.
- Turbocharger inlet and outlet bellows connections.
- Exhaust gas boiler, economiser and SCR reactor inlet flanges.
- Silencer and spark-arrestor inlet and outlet flanges.
- Wet exhaust and seawater-cooled exhaust mixing sections.
Quality and compliance
Marine exhaust gas bellows flanges are produced under Ningbo Ruican’s IATF 16949 certified quality management system, with melt-controlled chemistry, solution annealing and documented heat-treatment charts for every batch. EN 10204 3.1 certification is issued as standard, and EN 10204 3.2 certification is available when the buyer’s representative or nominated class society surveyor countersigns. Dye penetrant testing of all machined surfaces and weld preparations, radiographic or ultrasonic examination of the weld neck where specified, and hydrostatic or pneumatic pressure testing of the assembled bellows are performed to your specification, and witness testing by your nominated class society (LR, DNV, ABS, BV, CCS, NK or other) can be arranged on request. Ningbo Ruican does not claim class-society type approval; approval of the completed exhaust installation rests with the shipyard and the flag administration.
FAQs
Which material should I specify for a wet exhaust system?
For wet, seawater-cooled sections with high chloride content we recommend duplex 2205 or super-duplex 2507. CF8M / 316L remains suitable for dry exhaust runs at moderate temperature, and nickel-aluminium bronze C95800 is used where the flange mates to bronze or copper-nickel pipework.
Can you machine the bellows weld preparation?
Yes. The weld-prep land is machined to the geometry on your welding procedure specification, with the surface finish and chamfer angle controlled so the bellows manufacturer can achieve a consistent full-penetration weld.
Do you pressure test the flange?
The flange itself is a non-pressure part, but we hydrostatic or pneumatically test the assembled bellows and flange assembly at 1.5 times design pressure when you supply the bellows or when we manage the sub-assembly, and we issue a test certificate.
What flange standards can you drill to?
We drill to any specified standard, including DIN, EN, ANSI / ASME, JIS and yard-specific patterns. Send the bolt circle, hole size, pitch and facing detail with your enquiry.
Is intergranular corrosion testing available?
Yes. On request we perform intergranular corrosion testing to ASTM A262 Practice E and ferrite measurement on duplex grades, with results reported in the material certification package.
