What Is an HDPE Flange Connection?
An HDPE flange connection is a detachable joint that joins high-density polyethylene (HDPE) pipe to valves, pumps, tanks, or metal pipelines using a flange assembly. Unlike permanent butt fusion joints, a flanged connection can be disassembled and reassembled — making it ideal for equipment that requires periodic maintenance.
The basic HDPE flange assembly consists of:
- ✅HDPE stub end (or flange adaptor) — fused to the HDPE pipe
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- ✅Ductile iron backing flange — provides the bolt-hole pattern and mechanical strength
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- ✅Gasket — creates the seal between flange faces
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- ✅Bolts, nuts, and washers — compress the gasket
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1.HDPE Stub End (Lap Joint Stub)
The most common type. A short HDPE sleeve is butt-fused to the pipe end, and a loose backing flange slides over it. The stub end’s back face rests against the backing flange.
Used with: Ductile iron or steel backing rings.
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2.HDPE Flange Adaptor (Flange Fitting)
A pre-molded HDPE fitting with an integrated flange face. It is socket-fused or butt-fused to the pipe in one piece. More compact than a stub end + backing ring combination.
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3.Ductile Iron Backing Flange (Backing Ring / Backup Ring)
The mechanical component that holds the stub end in place. Made from ductile iron (ASTM A536), available with painted or FBE fusion-bonded epoxy coating. Standard drilling patterns include ANSI B16.5 Class 150, EN 1092-1, and AWWA C207.
HDPE Flange vs. Steel Flange
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Feature
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HDPE Flange Assembly
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Steel Flange
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Weight
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Light — easy to handle
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Heavy — requires lifting equipment
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Corrosion Resistance
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Excellent — no coating needed
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Requires galvanizing or painting
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Installation
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Quick fusion + bolt-up
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Welding or bolting only
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Service Life
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50+ years, maintenance-free
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15–25 years, regular maintenance
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Leak Rate
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Zero leak with fused joints
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Prone to gasket aging and joint failure
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Cost
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Lower total cost over lifecycle
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Lower upfront cost, higher maintenance
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Flexibility
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Absorbs ground settlement and vibration
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Rigid — susceptible to fatigue cracks
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Please send your request to the email address:sales@mfgpipe.com (We will respond to you within 24 hours).
Step-by-Step Installation Guide
Step 1: Prepare the Pipe End
Cut the HDPE pipe square and deburr the end. Ensure the pipe end is clean and flat.
Step 2: Slide on the Backing Flange
Slide the ductile iron backing flange onto the pipe before fusing the stub end. Confirm the bolt holes align with the mating flange.
Step 3: Butt-Fuse the Stub End
Use a butt fusion machine to fuse the HDPE stub end to the pipe end. Follow standard fusion procedures: heat, butt, cool.
Step 4: Cool and Position
Allow the fusion joint to cool completely (do not move during cooling). Slide the backing flange into position behind the stub end collar.
Step 5: Install the Gasket
Place a compatible gasket (EPDM for water, NBR for oil/gas) between the stub end sealing face and the mating flange.
Step 6: Align and Bolt Up
Align bolt holes. Insert bolts with washers. Hand-tighten all bolts first, then torque them in a crisscross (star) pattern in 2–3 passes to ensure even gasket compression.
Step 7: Pressure Test
After assembly, perform a hydrostatic pressure test at 1.5× working pressure. Hold for 30 minutes and check for leaks.
Watch out: Do not over-torque. Over-tightening can crush the HDPE stub end or damage the gasket. Follow the bolt torque specification provided by the fitting manufacturer.
Flange Standards, Sizes & Pressure Ratings
Common Flange Standards
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Standard
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Region
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Typical Class / Pressure
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ANSI/ASME B16.5
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USA
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Class 150, Class 300
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EN 1092-1
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Europe
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PN6, PN10, PN16, PN25
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AWWA C207
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USA (water)
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Class D, E, F
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AS 4087
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Australia
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PN16, PN25
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JIS B 2220
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Japan
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10K, 20K
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Typical HDPE flange assemblies range from DN25 (1 inch) to DN600 (24 inches), with larger sizes available for custom projects.
Pressure depends on the pipe SDR:
- ✅SDR 17.6 → PN10 (10 bar)
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Common Problems & Troubleshooting
Problem 1: Flange Interface Leakage
- ✅Causes: Gasket aging, uneven bolt torque, warped flange face, dirt on sealing surface
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- ✅Solution: Replace gasket, re-torque in star pattern, clean flange faces, inspect for warping
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Problem 2: Stub End Cracking
- ✅Causes: Over-tightened bolts, impact damage, low-quality material
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- ✅Solution: Use proper torque, handle with care, specify PE100 virgin material
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Problem 3: Flange Alignment Issues
- ✅Causes: Pipe movement after fusion, thermal expansion, misaligned mating flange
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- ✅Solution: Allow cooling before positioning, use expansion loops for long runs, check alignment before bolting
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Problem 4: Corrosion on Backing Flange
- ✅Causes: Uncoated painted flange in buried or corrosive environment
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- ✅Solution: Specify FBE (fusion-bonded epoxy) coating for buried or corrosive service
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FAQ
What is the difference between a backing ring and a backing flange?
They are the same component. “Backing ring,” “backup ring,” and “backing flange” all refer to the ductile iron ring that provides bolt-hole support behind an HDPE stub end.
Can I reuse a ductile iron backing flange?
Yes, if it is free from cracks, deformation, and bolt hole damage. Inspect it carefully before reuse.
What gasket material should I use?
- ✅Water / wastewater: EPDM
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- ✅Oil / gas / hydrocarbons: NBR (nitrile)
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- ✅Chemical service: Consult chemical compatibility charts
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How do I choose between stub end and flange adaptor?
Stub end + backing ring is more cost-effective for large diameters. Flange adaptors are more compact and easier to install in tight spaces.
Looking for HDPE Flange Fittings?
At MfgPipe (Henan Lukuang Industry), we manufacture a complete range of HDPE flange fittings — stub flanges, ductile iron backing rings, flange adaptors, and butt fusion fittings — all in PE100/PE4710, certified to ISO 4427, EN 12201, and ASTM D3034.
[Request a Quote] — send your size, standard, and quantity, and we’ll reply within 24 hours with a factory-direct price.
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Please send your request to the email address:sales@mfgpipe.com (We will respond to you within 24 hours).
