Malleable iron pipe fittings are an important component of many plumbing, heating, and cooling systems. These fittings join pipes and tubing made of various materials, including iron, copper, brass and stainless steel.
What Are Malleable Iron Pipe Fittings?
Malleable iron pipe fittings are comprised of malleable iron, an alloy of iron and carbon (2-3%). The key benefit of malleable iron is that it can be “worked” – bent, stretched and formed – without fracturing like brittle materials. After forming, malleable iron returns to its original shape.
Common Types Of Malleable Iron Pipe Fittings Include:
- Elbows – These fittings join two pipes at right angles. Elbows come in angles from 22.5 to 180 degrees.
- Tees – T-shaped fittings with three openings that join three pipes at right angles.
- Couplings – Used to join two pipes end-to-end. Couplings cover the cut ends of the pipes.
- Bushings – Short reducers that transition from a large pipe size to a smaller one.
- Reducers – Fittings that transition from a large pipe size to a smaller one over a longer length.
- Caps – Close the end of a pipe. Caps are threaded or soldered onto the pipe end.
- Unions – Allow pipes to be joined and separated easily for repair or replacement.
Malleable iron fittings are threaded to screw onto pipe threads. The common thread types are NPT (national pipe thread) and BSP (British standard pipe).
Properties of Malleable Iron
The key properties of malleable iron that make it suitable for pipe fittings are:
- Ductility – Malleable iron’s ability to be “worked” allows for precise shaping and threading of fitting sockets and threads.
- Strength – Malleable iron fittings retain strength after forming due to their alloy composition and heat treatment process.
- Corrosion resistance – fittings made of malleable iron resist rust and corrosion better than plain iron. However, they still require protective coatings for prolonged lifespan.
- Thermal stability – Malleable iron fittings maintain their shape and strength over a wide range of operating temperatures.
- Cost effectiveness – Malleable iron is more affordable than alternative materials like bronze or brass.
Manufacturing Process
Malleable iron fittings are produced through a multi-step process:
- The appropriate composition of iron and carbon is melted to form an alloy ingot.
- The ingot is then cast into semi-finished fittings through die-casting.
- The fittings undergo heat treatment that involves heating and cooling cycles. This converts the iron microstructure to malleable form.
- Fittings are then formed or bent into their final shape using presses and dies. Threads are cut on the ends.
- Fittings are annealed or re-heated to relieve internal stresses from forming.
- Finished fittings undergo surface treatment like passivation, painting or galvanizing for corrosion resistance.
Advantages Of Malleable Iron Fittings
- Ductility allows bending without cracking for custom installations
- Strength is comparable to steel but with lower material cost
- Wide range of sizes and configurations available as standard parts
- Ease of joining through threaded connections
- Fair corrosion resistance with proper surface treatment
- Good resistance to water hammer due to elasticity
- Ability to withstand mechanical vibration and thermal expansion/contraction
Applications of Malleable Iron Fittings
Due to their combination of strength, formability and cost, malleable iron fittings find applications in:
- Plumbing systems – For joining water, waste, vent and gas piping
- Heating systems – Connecting radiators, boilers, baseboard heaters and air ducts
- Cooling systems – Joining pipe runs for water-based air conditioners and coolants
- Industrial settings – Connecting pipe networks for chemicals, compressed air and steam