How Is Copper Tube Made? The Complete Manufacturing Guide

Copper tube is made through a multi-stage industrial process that begins with refined copper billets and ends with precisely dimensioned, seamless or welded tubes ready for plumbing, HVAC, refrigeration, and industrial use. The core steps are melting, casting, extrusion or piercing, drawing, annealing, and finishing — each stage tightly controlled to meet international standards such as ASTM B88, EN 1057, or GB/T 18033.

Understanding how copper tube is manufactured helps buyers evaluate quality, choose the right supplier, and specify the correct tube type for their application. This article breaks down every major stage of copper tube production, with real process data and factory-level detail.

Raw Materials: What Goes Into a Copper Tube

The starting point for any copper tube factory is high-purity copper. Most manufacturers use electrolytic tough pitch (ETP) copper (C11000), which contains a minimum of 99.9% copper. Some specialized tubes — particularly for medical gas or semiconductor applications — require oxygen-free copper (OFE, C10200) with purity above 99.99%.

Raw copper arrives at the factory either as:

• Cathode copper plates (from electrolytic refining)
• Pre-cast copper billets or logs
• High-grade copper scrap (for recycled-content products)

Copper is one of the most recycled industrial metals in the world. Over 30% of global copper supply comes from recycled scrap, and many tube factories blend virgin and recycled copper while still meeting purity requirements for standard tube grades.

Step 1 — Melting and Casting the Copper Billet

The first production step in a copper tube factory is melting the raw copper in a channel induction furnace or coreless induction furnace at temperatures between 1,083°C and 1,150°C (the melting point of pure copper is 1,083°C). The molten copper is held and degassed to remove dissolved oxygen and hydrogen, which would otherwise cause porosity defects in the final tube.

The refined melt is then cast into billets or hollow shells using one of two primary methods:

• Continuous casting (up-cast or horizontal cast): The most common method in modern copper tube factories. Produces long, uniform billets with consistent grain structure. Speeds typically range from 0.5 to 2.5 m/min depending on billet diameter.
• Semi-continuous (direct chill) casting: Used for larger-diameter billets, typically above 200mm. The mold is water-cooled, solidifying the copper rapidly to reduce segregation.

The resulting billet — typically 80mm to 300mm in diameter and 500mm to 3,000mm long — is surface-scalped by a lathe to remove surface oxides and casting skin before the next stage.

Step 2 — Extrusion or Piercing: Creating the Hollow Tube Shell

This is where the solid billet is converted into a hollow tube shell. There are two dominant methods used across copper tube factories:

Hot Extrusion

The billet is heated to approximately 800°C to 900°C and placed in a hydraulic extrusion press. A mandrel pierces the center while the copper is forced through a die, producing a thick-walled hollow shell called a mother tube or extrusion shell. Extrusion presses in copper tube production typically operate at forces between 10 MN and 50 MN. Extrusion ratios (the ratio of billet cross-section to tube cross-section) commonly range from 20:1 to 80:1.

Rotary Piercing (Mannesmann Process)

Used for larger diameter seamless tubes, this method involves feeding a heated solid billet between two angled rolls. The rolls create internal stresses that open a central cavity, which is then shaped by a piercing plug. This process is more common in steel tube production but is also applied in some copper tube factories for large-OD products.

After extrusion or piercing, the tube shell has rough dimensional tolerances and a relatively thick wall — it must be drawn down to final dimensions in subsequent steps.

Step 3 — Cold Drawing: Achieving Precise Dimensions

Cold drawing is the most critical dimensional control stage in copper tube manufacturing. The extruded shell is pulled through a series of progressively smaller dies — each pass reducing the outer diameter and wall thickness while increasing the tube's length and improving surface finish.

Each cold draw pass typically reduces the cross-sectional area by 20% to 45%. Multiple draw passes are required to reach the final specification. A tube starting as a 60mm OD shell might be drawn through 4 to 8 passes to reach a final 15mm OD with a 1mm wall thickness.

Two main drawing techniques are used:

• Floating plug drawing: A plug inside the tube controls the inner diameter while the outer die controls OD. Ideal for long coils and small-diameter tubes (below 28mm).
• Fixed mandrel drawing: A mandrel rod is used for tighter ID tolerances. Common for straight-length tubes above 25mm OD.

Drawing speeds in modern copper tube factories reach 100 to 400 m/min on bull block (coil) machines for small-diameter tubes. Lubricants (typically oil-based or emulsion-type) are applied at the die entry to reduce friction and die wear.

Step 4 — Annealing: Restoring Ductility

Cold drawing work-hardens the copper, making it stiffer and more brittle with each pass. Annealing — controlled heat treatment — is applied between drawing passes and/or after final drawing to restore ductility and achieve the required temper designation.

Common annealing methods in copper tube factories include:

• Batch (bell) furnace annealing: Coils or bundles of tube are annealed in a sealed furnace with a protective atmosphere (typically nitrogen or a nitrogen-hydrogen mix) at 400°C to 650°C for several hours. Prevents surface oxidation.
• Continuous strand annealing: The tube passes through an inline furnace at high speed. Used for smaller-diameter coil tube. Temperatures are higher (up to 800°C) but exposure time is very short (seconds).
• Induction annealing: Electromagnetic induction heats the tube rapidly and uniformly. Suitable for precise temper control.

Step 5 — Straightening, Cutting, and Surface Finishing

After final drawing and annealing, tubes undergo mechanical straightening on a roller straightener to meet bow and straightness tolerances (typically ≤1.5mm per meter under ASTM B88). Coiled product is wound onto spools or formed into pancake coils — standard coil lengths range from 15 meters to 50 meters for residential plumbing tube.

Straight lengths are cut to standard sizes (commonly 3m, 4m, 5m, or 6m) using rotary cut-off machines that leave clean, burr-free ends. Some copper tube factories offer deburring and end-chamfering as standard, particularly for tube supplied to press-fit or push-fit fitting systems.

Surface finishing options available at the factory level include:

• Bright/clean finish: Standard for most plumbing and HVAC tube. Achieved by annealing in protective atmosphere.
• Passivated finish: Chemical treatment to enhance corrosion resistance for outdoor or marine environments.
• Internally cleaned and capped: Required for medical gas, refrigeration (ACR), and food-grade applications to prevent contamination from oil residues or particulates.

Step 6 — Quality Testing and Inspection

A reputable copper tube factory subjects every production batch to a rigorous quality assurance protocol before shipment. Key tests include:

• Eddy current testing (ECT): Inline, 100% inspection for surface and subsurface defects. Detection sensitivity can identify defects as small as 0.1mm in depth.
• Hydrostatic pressure test: Tubes are pressurized with water (typically at 1.5× to 2× the rated working pressure) and held for a defined period to confirm leak integrity.
• Dimensional inspection: OD, wall thickness (WT), ovality, and length are measured by laser gauges and contact micrometers. Tolerances for ASTM B88 Type K tube, for example, allow WT variation of ±10%.
• Tensile and hardness testing: Mechanical properties (yield strength, tensile strength, elongation) verified against standard limits per temper.
• Chemical composition analysis: OES (optical emission spectrometry) or XRF used to verify copper purity and alloy content.

Factories certified to ISO 9001 maintain full traceability from raw material heat number to finished tube lot. Leading manufacturers also hold product certifications such as NSF/ANSI 61 (for drinking water), EN 1057 (European plumbing), or DEWA/WRAS approvals for specific markets.

Seamless vs. Welded Copper Tube: How They Differ in Production

Not all copper tube is seamless. While seamless copper tube — produced by the extrusion/drawing process described above — dominates most plumbing, HVAC, and refrigeration markets, welded copper tube is also manufactured for specific applications.

Welded copper tube is formed by feeding a copper strip through a series of forming rolls that gradually shape it into a round cross-section, then resistance-welding or TIG-welding the seam. After welding, the tube is typically drawn cold to improve dimensional accuracy and seam integrity.

Specialty Copper Tube Products Made at the Factory

Modern copper tube factories produce a wide range of specialized tube types beyond plain round tube. These include:

• Inner-grooved (IG) tube: The inner surface is rolled with helical grooves using a grooved plug during the drawing process. Used in air conditioning and heat pump systems, IG tube improves heat transfer efficiency by 20% to 40% compared to smooth-bore tube.
• Finned tube: Longitudinal or spiral fins are formed on the outer surface for use in heat exchangers.
• Capillary tube: Very small OD (typically 0.5mm to 6mm) and tight tolerances, produced by multi-pass drawing. Used in refrigeration flow control and medical devices.
• Corrugated flexible tube: Mechanically corrugated after drawing for flexibility in gas and water installations.
• Alloy tube: Brass (copper-zinc), cupronickel (copper-nickel), and bronze tubes produced using the same equipment but with different alloy billets, targeted at marine, industrial, and high-temperature applications.

What to Look for When Evaluating a Copper Tube Factory

When sourcing from a copper tube factory — whether domestic or overseas — the following indicators distinguish a high-quality manufacturer from a low-cost but unreliable one:

1. Vertical integration: Factories that control their own melting, casting, and drawing operations have tighter quality control than those that outsource early-stage processing.
2. Inline inspection technology: 100% eddy current testing and laser dimensional gauging should be standard, not optional.
3. Certifications relevant to your market: NSF 61, EN 1057, ASTM B88, GB/T 18033, WRAS — confirm that the factory's certification scope covers your specific tube type, OD, and temper.
4. Mill test reports (MTRs): Reliable factories provide heat-specific MTRs showing chemical composition, mechanical test results, and hydrostatic test confirmation.
5. Capacity and lead time: A factory capable of producing 50,000 to 200,000 tons per year has the scale to handle surge orders without quality compromise. Verify stated capacity against actual equipment count.
6. Packaging and protection: Tubes for export should be protected with PVC end caps, polyethylene film wrapping, and wooden crating. Poor packaging leads to in-transit damage and contamination that can void certification compliance.