Custom Pipe Flanges: How to Specify Custom Flanges for Industrial Projects

Custom pipe flanges are used when a standard catalog flange cannot fully match the pipe, equipment nozzle, pressure class, bolt pattern, material requirement or installation space. For export projects, a small mistake in bore, facing or bolt-hole position can delay installation for weeks, so the best custom flange order starts with clear technical information.

This guide explains how engineers and buyers can specify custom flanges with fewer revisions, better quality control and clearer communication with the manufacturer.

When Do You Need Custom Pipe Flanges?

Standard ASME, ANSI, DIN, JIS or EN flanges cover many common piping connections. Custom pipe flanges become necessary when the project has a special size, non-standard thickness, large diameter, unusual drilling pattern, special facing, equipment connection or material requirement that cannot be solved with a regular flange.

Typical examples include replacement flanges for old equipment, pressure vessel nozzles, pump and valve adapters, marine piping, skid-mounted systems, water treatment equipment, chemical pipelines and OEM machinery. In these cases, custom flanges help the piping system fit the real site condition instead of forcing the site to fit the catalog.

Information to Prepare Before Requesting a Quote

A good RFQ for custom pipe flanges should give the manufacturer enough information to check feasibility, estimate machining time and confirm inspection requirements. At minimum, include the following details:

• Nominal pipe size, actual outside diameter and pipe schedule or wall thickness.
• Flange type: weld neck, slip on, blind, threaded, socket weld, plate, lap joint or special design.
• Pressure class or design pressure and design temperature.
• Material grade, such as ASTM A105, 304 stainless steel, 316 stainless steel, alloy steel or duplex stainless steel.
• Face type and finish, including raised face, flat face, ring type joint or custom groove.
• Bolt-hole quantity, bolt size, bolt circle diameter and drilling orientation.
• Required standard, drawing number, tolerance, inspection level and certificate documents.
• Quantity, delivery schedule, packing requirement and destination country.

Drawings Matter More Than Long Messages

For custom flanges, a drawing is usually more reliable than a long email description. A simple drawing should show outside diameter, bore, thickness, hub dimensions, raised face height, gasket surface, bolt circle, hole diameter, hole quantity and any bevel or groove detail.

If the flange connects to existing equipment, photos and measured dimensions are also helpful. For repeat orders, send the previous drawing or purchase order number. This reduces the chance of mixing different standards or manufacturing the wrong drilling pattern.

Material Selection for Custom Flanges

Material should be selected according to fluid, pressure, temperature, corrosion risk, welding method and required documentation. Carbon steel custom pipe flanges are common for general industrial piping and high-strength applications. Stainless steel custom flanges are used for corrosion resistance, food-grade service, chemical processing and marine environments.

For aggressive media or high temperature service, alloy steel, duplex stainless steel or special materials may be required. If the project requires traceability, ask for mill test certificates, heat number marking and positive material identification before shipment.

Choosing the Right Flange Type

The best custom flange type depends on how the connection will be installed and loaded. Weld neck flanges are preferred for high pressure, temperature cycling and critical service because the hub supports stress transition. Slip on flanges are easier to install for lower pressure systems. Blind flanges close pipe ends or equipment openings. Lap joint flanges help with bolt alignment and maintenance when used with stub ends.

For OEM equipment, the flange may combine several features, such as a non-standard bore, special step, double drilling pattern or machined locating face. These details should be reviewed before production, not after the parts arrive at site.

Standards and Tolerances

Even custom pipe flanges should be anchored to a recognized standard whenever possible. ASME B16.5, ASME B16.47, EN 1092-1, DIN, JIS, GOST and API-related requirements are often used as the base. The custom portion may be the bore, thickness, face, material, bolt pattern or outside diameter.

Clear tolerances help both sides understand what will be inspected. For example, bolt-hole position, face flatness, bore size and gasket surface roughness can be critical for sealing. If the flange is for replacement, check whether the existing mating flange follows a real standard or an old plant-specific drawing.

Inspection and Quality Documents

Custom flanges should be inspected before packing. Common checks include dimension inspection, visual inspection, material certificate review, marking, surface finish and packaging condition. Depending on service, the order may also require ultrasonic testing, magnetic particle testing, liquid penetrant testing, hardness testing, PMI or pressure-related verification.

For export orders, confirm documentation language, certificate format, marking style and packing list requirements in advance. This makes customs clearance and project handover smoother.

How to Reduce Lead Time

Lead time is strongly affected by material availability, forging or plate thickness, heat treatment, CNC machining time, inspection and approval drawing feedback. Buyers can reduce delays by sending complete drawings, confirming material substitutes early and approving technical drawings quickly.

For urgent custom flanges, ask the manufacturer what material is already in stock and whether the design can be adjusted without changing the sealing function. Sometimes a small change in thickness, material grade or blank size can shorten production time significantly.

Common Mistakes When Ordering Custom Pipe Flanges

• Sending only nominal size without actual bore or pipe schedule.
• Confusing raised face and flat face requirements.
• Forgetting bolt circle diameter or hole orientation.
• Ordering stainless steel parts without confirming certificate requirements.
• Using a standard drawing when the mating equipment is actually non-standard.
• Approving production before checking gasket and bolt compatibility.

FAQ About Custom Flanges

What are custom pipe flanges?

Custom pipe flanges are flange components made to special dimensions, materials, pressure requirements, drilling patterns or equipment connection details when a standard flange is not enough.

What details are required for custom flanges?

Send size, material, pressure class, standard, drawing, bore, thickness, face type, bolt pattern, quantity, inspection requirement and delivery destination.

Can custom flanges still follow ASME or DIN standards?

Yes. Many custom flanges use ASME, DIN, EN or JIS as the base standard, with only selected dimensions or machining details customized for the project.

Need Custom Pipe Flanges for Your Project?

Songhai Flange supplies standard and custom flanges for industrial piping, pressure vessels, chemical equipment, marine systems, water treatment and OEM projects. If you need custom pipe flanges made from carbon steel, stainless steel or alloy steel, our team can support drawing review, material selection, machining, inspection and export packing.