Fabricated or Moulded: Which Fitting is Best?
“Fabricated vs moulded fittings, which one should I choose?” When it comes to HDPE pressure pipe systems, this is one of the most common questions we get.
The answer isn’t just about price. It’s about pressure ratings, durability, and safety. Choosing the wrong type without understanding the engineering differences can lead to significant de-rating of your pipeline’s capacity.
In this guide, Nathan Craig, CEO of Advanced Piping Systems, breaks down the key differences to help you make the right choice for your project.
Fabricated vs Moulded Fittings: The Core Difference
(1) Moulded Fittings
Moulded fittings are manufactured via injection moulding as a single, solid unit. High-quality European moulded fittings are designed with integral reinforcement—extra material thickness in high-stress areas, such as the crotch of a tee or the sweep of an elbow.
Key Benefit: This reinforcement allows a PN16 moulded fitting to be rated for full PN16 operation. You do not need to derate it.
(2) Fabricated (Segmented) Fittings
Fabricated fittings are made by cutting HDPE pipe into segments and butt-welding them together to form shapes. While they are excellent for large-diameter custom work, the welding process introduces stress points.
Key Limitation: Fabricated fittings must be derated. You cannot run them at the same pressure as the pipe they are made from.
Expert Insight
Why We Recommend Moulded
According to Nathan Craig, the choice often comes down to long-term reliability and simplicity.
“We always suggest European moulded fittings over fabricated ones. They provide the best value for money and longevity. Fabricated fittings should generally only be used in low-pressure systems or where moulded sizes simply don’t exist.”
— Nathan Craig, CEO, Advanced Piping Systems
This advice is backed by industry standards. Fabricated fittings lack the continuous structural integrity of a moulded piece, resulting in significantly lower pressure-handling capability.
Understanding Deration Factors
One of the biggest traps for engineers is assuming a fabricated fitting has the same pressure rating as the pipe.
“If you manufacture a segmented tee from PN16 pipe, the fitting itself is effectively rated to only PN8,” explains Nathan.
This is due to the deration factor. The PIPA guidelines (Pop Industry Council of Australia) mandate that segmented fittings must have their operating pressure reduced to account for the stress on the mitred welds.
Typical Deration Rules:
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Segmented Bends (<30°): 0.8 factor (20% reduction)
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Segmented Bends (>30°): 0.6 factor (40% reduction)
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Segmented Tees: 0.5 factor (50% reduction)
The Result: To get a PN16 rating on a fabricated tee, you would often need to start with much thicker, heavier pipe (like PN25), which increases cost and weight.
Summary: Which Fitting is Best?
For most standard pressure applications (water, slurry, gas), moulded fittings are the superior choice. They offer:
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Full pressure rating without complex calculations.
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Integral reinforcement for safety.
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Better long-term durability.
However, fabricated fittings remain a vital solution for:
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Non-standard angles (e.g., a 17-degree bend).
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Large diameters where moulded options don’t exist.
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Low-pressure applications (drainage/vents) where deration doesn’t matter.
Frequently Asked Questions (FAQ)
Do I need to derate a moulded elbow?
No. Quality moulded elbows are designed to operate at their full nominated pressure rating (e.g., a PN16 elbow is rated for 16 bar).
Why are fabricated fittings weaker?
The process of cutting and welding pipe segments creates “mitred” joints. These joints experience higher stress concentrations than a smooth bend, requiring the pressure rating to be lowered (derated) for safety.
Can I use fabricated fittings for high-pressure lines?
Yes, but you must use a much thicker pipe class to compensate for the deration factor. This often makes them heavier and more expensive than the moulded equivalent.
To explore Advanced Piping System’s full range of moulded and fabricated fittings, view our Product page, or contact us today.
