Marine Inner Weld Flanges
Marine Inner Weld Flanges, also known as Composite Weld Neck Inner Flanges, are specialized flange assemblies developed for demanding marine and offshore piping applications. The design combines a corrosion-resistant alloy flange face with a carbon steel backing ring, creating a durable and cost-effective connection solution.
This composite construction provides the mechanical strength required for high-pressure piping systems while reducing overall component weight. By separating the corrosion-resistant wetted surface from the structural backing flange, Composite Weld Neck Inner Flanges help minimize galvanic corrosion risks, extend service life, and reduce maintenance requirements in harsh marine conditions.
Marine Inner Weld Flanges for shipboard seawater piping, offshore systems and CuNi pipe connections. Available as 5K Inner Weld Flange, 10K Inner Weld Flange and JIS Marine Flange solutions, with CuNi 90/10 C70600 wetted parts and matching backing rings.
- Main Product: Marine Inner Weld Flanges
- Types: 5K Inner Weld Flange, 10K Inner Weld Flange
- Material: CuNi 90/10 C70600, CuNi 70/30 on request
- Backing Ring: Carbon steel, galvanized steel, painted steel, stainless steel
- Standards: ASME B16.5, DIN 86037, EEMUA 234, shipyard drawings
- Applications: Seawater cooling, ballast, fire water, offshore piping, pump and valve connections
Inner Weld Flanges for Marine Seawater Piping
Marine Inner Weld Flanges are specialized flange components used in marine piping systems where the flange connection must handle seawater, vibration, humidity and long operating cycles.
In a composite flange assembly, the inner weld flange is the part welded to the pipe and exposed to the internal fluid. For seawater service, this part is commonly made from CuNi 90/10 C70600 copper nickel alloy because of its reliable resistance to seawater corrosion, erosion and marine growth.
Marine Inner Weld Flanges are widely used by shipyards, marine repair yards, offshore contractors and equipment manufacturers for seawater cooling lines, ballast water systems, fire-fighting water systems, pump connections and valve connections.
Why This Design Is Used Onboard
- The CuNi inner flange protects the wetted area from seawater corrosion.
- The loose backing ring makes bolt alignment easier during installation.
- The composite design reduces the amount of copper nickel material required.
- The flange connection is suitable for compact shipboard piping spaces.
- The design works well with CuNi pipe systems used in marine and offshore service.
5K Inner Weld Flange and 10K Inner Weld Flange
| Flange Type | Typical Use | Material and Assembly | Notes |
| 5K Inner Weld Flange | Low-pressure marine seawater and service water piping systems | CuNi 90/10 C70600 inner flange with carbon steel or stainless steel backing ring | Commonly selected for JIS marine flange systems where 5K pressure class is specified. |
| 10K Inner Weld Flange | Marine pipelines requiring a higher pressure class than 5K systems | CuNi 90/10 C70600 inner flange, optional CuNi 70/30 for demanding service | Suitable for JIS Marine Flange connections in seawater cooling, pump and valve lines. |
| Custom Inner Weld Flange | Replacement work, special equipment interfaces and non-standard pipe connections | CuNi 90/10, CuNi 70/30, carbon steel backing ring, stainless steel backing ring | Can be manufactured according to drawings, samples or project data sheets. |
CuNi 90/10 C70600 for Seawater Corrosion Resistance
CuNi 90/10, also known as C70600 copper nickel alloy, is one of the most widely used materials for marine seawater piping and flange fittings.
The alloy contains approximately 90% copper and 10% nickel, with small additions of iron and manganese. This composition gives the material stable performance in flowing seawater, especially where ordinary carbon steel would suffer from rapid corrosion.
For Marine Inner Weld Flanges, CuNi 90/10 C70600 is usually selected for the inner wetted part. The material is compatible with copper nickel pipework and helps maintain a clean internal flow path over long service periods.
In higher velocity seawater lines or more demanding offshore environments, CuNi 70/30 can also be reviewed according to the system design and owner requirement.
Material Advantages
- Excellent seawater corrosion resistance
- Good resistance to erosion and impingement attack
- Natural resistance to marine biofouling
- Good weldability with CuNi pipe systems
- Reliable service life in shipboard and offshore pipelines
- Suitable for seawater cooling, fire water and ballast systems
Haomei Full Range of CuNi 90/10 Copper Nickel Flange Fittings
We also supply a full range of CuNi 90/10 C70600 copper nickel flange fittings for marine and offshore piping systems, including stub end, slip-on, welding neck, socket weld, threaded and blind flange types.
These CuNi flange fittings are designed to provide excellent seawater corrosion resistance and long-term reliability in harsh marine environments. They can be used together with Marine Inner Weld Flanges or supplied separately for newbuilding, retrofit, maintenance and offshore piping projects.
Used with loose backing rings where easy alignment and corrosion-resistant wetted surfaces are required.
A practical option for marine pipe connections where slip-on installation and CuNi seawater resistance are needed.
Designed for welded pipe connections where strength, smooth transition and pressure performance are important.
Commonly used for general marine piping systems with straightforward welding and installation requirements.
Suitable for smaller pipe sizes and systems requiring a strong socket weld connection.
Used in selected marine service lines where threaded connection is specified by the system design.
Used to close pipe ends, valve outlets and equipment nozzles in seawater and marine service systems.
Available in 5K, 10K and project-specific designs for JIS Marine Flange and CuNi pipe systems.
Marine Flange Standards, Pressure Ratings and Material Specifications
Marine flange dimensions vary depending on international standards, shipyard practices, and owner specifications. We recommend confirming the drawing or flange table before production.
| Category | Available Options | Production Notes |
| Marine Standards | EEMUA 234, ASME B16.5, DIN 86037, and project-specific marine specifications | Commonly used for CuNi seawater pipework, shipboard systems, and offshore piping packages. Ensure compliance with project drawings. |
| Pressure Ratings | 5K, 10K, 14 bar, 16 bar, 20 bar, and custom pressure classes | Final pressure selection should match piping design, medium, temperature, and project requirements. |
| Main Materials | CuNi 90/10 C70600, CuNi 70/30, carbon steel, stainless steel | CuNi is typically used for the wetted side, while backing rings can be supplied in coated carbon steel or stainless steel to prevent galvanic corrosion. |
| Documents | Material certificate, dimensional report, inspection report, packing list | Additional documentation can be prepared according to purchase order or project specifications. |
Where Marine Inner Weld Flanges Are Used
Marine Inner Weld Flanges and related CuNi flange fittings are used wherever seawater corrosion resistance and dependable pipe connections are important.
- Seawater cooling systems
- Ballast water pipelines
- Fire-fighting water systems
- Bilge and drain systems
- Deck wash lines
- Offshore platform seawater systems
- Desalination equipment piping
- Heat exchanger connections
- Pump inlet and outlet connections
- Valve connection points
- Ship repair replacement parts
- Marine machinery piping packages
For JIS-based projects, 5K Inner Weld Flange and 10K Inner Weld Flange types are frequently requested. For European or international projects, DIN 86037, EEMUA 234 or owner-specific drawings are commonly used.
Manufacturing, Inspection and Delivery of Marine Flanges
Ensuring a precise fit before welding and long-term reliability after installation is critical for marine flange connections. Every stage—from material selection to final shipment—is carefully monitored, with strict control over traceability, machining accuracy, and quality inspections.
Quality Inspection Process
- Verification of raw materials and compliance with specifications
- Checking material certificates and documentation
- Inspection of flange outside diameter and bore dimensions
- Measurement of flange thickness, hub dimensions, and welding ends
- Sealing face quality check for leak-proof connections
- Bolt hole position and diameter verification
- Fit-up and alignment inspection before welding
- Surface condition assessment for corrosion resistance
- Final packing inspection to ensure safe transport
Packing and Shipping
Marine Inner Weld Flanges, JIS Marine Flanges, and CuNi flange fittings are carefully packed to protect machined surfaces during handling and transportation. Packing options include export-grade wooden cases, pallets, or customized packaging tailored to order size and shipping requirements.
Products are available as individual flanges, matched flange and backing ring sets, or complete CuNi flange fitting packages, providing a flexible solution for marine piping projects and offshore installations.
Send Your Marine Flange Inquiry
We supply Marine Inner Weld Flanges, 5K Inner Weld Flange, 10K Inner Weld Flange and JIS Marine Flange components for shipbuilding, ship repair and offshore piping systems.
We also supply CuNi 90/10 C70600 copper nickel flange fittings, including CuNi Stub End Flange, CuNi Slip-On Stub End Flange, CuNi Welding Neck Flange, CuNi Slip On Flange, CuNi Socket Weld Flange, CuNi Threaded Flange and CuNi Blind Flange.
If you have drawings, flange tables or a piping material list, send them to our team. We will check the size, material, pressure class and backing ring requirement before quotation.
Information Needed for Quotation
- Product type
- 5K, 10K or other pressure class
- ASME B16.5, DIN 86037, EEMUA 234 or drawing
- Nominal pipe size
- Pipe outside diameter
- Material: CuNi 90/10 C70600 or other grade
- Backing ring material
- Quantity
- Application system
- Required certificates
- Surface treatment requirement
- Delivery destination
FAQ – Marine Inner Weld Flanges
What are Marine Inner Weld Flanges?
Marine Inner Weld Flanges are inner flange components welded to marine pipes. In composite flange assemblies, they are usually combined with loose backing rings to create bolted pipe connections for seawater and service water systems.
Can you supply 5K Inner Weld Flange and 10K Inner Weld Flange?
Yes. We supply both 5K Inner Weld Flange and 10K Inner Weld Flange for JIS Marine Flange applications. Dimensions can be produced according to JIS standards, shipyard drawings or project requirements.
Why is CuNi 90/10 C70600 used for these flanges?
CuNi 90/10 C70600 has strong resistance to seawater corrosion, erosion and marine biofouling. It is widely used for shipboard and offshore seawater piping systems.
Do you only supply Marine Inner Weld Flanges?
No. We also supply a full range of CuNi 90/10 copper nickel flange fittings, including CuNi Stub End Flange, CuNi Slip-On Stub End Flange, CuNi Welding Neck Flange, CuNi Slip On Flange, CuNi Socket Weld Flange, CuNi Threaded Flange and CuNi Blind Flange.
Can you manufacture according to drawings?
Yes. Custom Marine Inner Weld Flanges and JIS Marine Flange components can be produced according to drawings, samples, material lists or shipyard specifications.
What are Marine Inner Weld Flanges used for?
Marine Inner Weld Flanges are used in ship and offshore piping systems to create corrosion-resistant welded connections. They are commonly used in seawater cooling, ballast water, fire water and other marine service pipelines.
Which standards can be supplied?
Common standards include DIN 86037 and EEMUA 234. Products can also be manufactured according to shipyard drawings, offshore project specifications or customer-provided technical requirements.
What pressure ratings are commonly available?
Common pressure ratings include 14 bar, 16 bar and 20 bar. Other ratings can be checked according to the drawing, pipe size and project requirement.
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