Metal Tubing 101



The use of pipes or tubes have been around for thousands of years, although technically the term ‘tube’ is used to imply heightened engineering qualities and are normally custom made. Different industrial needs call for different types of metal tubes. They can be categories into the two types of Electrical metal tubes and mechanical metal tubes. Mechanical metal tubes are designed for structural applications while electrical tubes are meant to contain electrical wires.

Different materials are used in the making of metal tubes and these include; aluminum, brass, bronze, copper, gold, titanium, platinum, silver, steel and stainless steel. The end purpose of the product will generally determine the material used. This is because some materials are very corrosive in nature and cannot be used in sensitive industries, say the pharmaceutical one.

Brief History

As mentioned above, the use of metal tubes has been around for thousands of years or at least the idea of it. Ancient agriculturalists used them to divert water from rivers and streams into their fields. Bamboo tubes were used in more tropical areas to transport water while evidence of clay tube use has been discovered from ancient civilizations. Other material used was wood.

The early 1800s saw the first modern-day welded steel tube development when William Murdock invented a coal burning lamp system. Over the years, methods to producing quality metal tubes have been changed and revisited to what we have today.

How metal tubes are made

The basic raw material to metal tube production is steel, more so iron. Other materials used include titanium, aluminum, vanadium, tungsten, zirconium and manganese. Stainless steel is used in the manufacture of metal tubes for use in water transportation as well as oil and gas distribution. This is because they have desirable qualities as compared to certain manmade materials that tend to have unwanted or unknown exposure effects. Steel tubes can also be used for structural support in buildings and vehicles.

A process that heats and molds a solid billet into a cylindrical shape is used in the manufacture of seamless tubes. Once the material has been heated, it is then rolled until it is stretched and hollowed. To do away with irregular shapes in the harrowed center, during the rolling process, a bullet-shaped piercer point is pushed through the middle of the billet.

Once the rolling and stretching is done, depending on where the tube will end up, some other materials may be applied. For example, sulfuric acid may be used to clean the tube or in case of coated tube, a light amount of oil may be applied to the tube at the end of the production line.

Metal tube forms

In terms of design, the end product will depend on the end-use. Two types of steel metal are available; one that has a single welded seam along its length and one that is seamless. The seamless varieties are normally used in the transportation of liquids and tend to weigh less. Seamed metal tubes on the other hand tend to be more rigid, weigh more and are used in electrical conduits, plumbing and transportation. In essence, they are utilized in situations that don’t call for a lot of stress to be applied to the tube.

In terms of the tube diameter, again, the end-use will determine this during production. There is a wide range of diameters to be used, from those to be used in tiny pipes to those that will be used in large pipes. The thickness of the wall can also be controlled during the production process. Other characteristics that can be controlled during production include the tube length, coating material and the finishing touches.

Manufacturing process

Basically, three steps or methods are utilized in the manufacture of steel metal tubes. The three steps include; the raw steel being converted into a workable form, the tube being formed on a continuous or semi continuous production line and the tube being cut and modified with respect to the end-user’s needs. Generally speaking though, the method or process utilized in manufacturing metal tubes will depend on the process’ interaction with the type of steel to be used in addition where the end-product will be used.

A look at the manufacturing process with respect to the tubing classifications:

  • Seamless steel tubes are formed through extrusion. Such tubes can be formed in a hot or cold process.
  • Electric resistant welded (ERW) or As-welded. With this method, a small weld is formed as a result of a sheet of steel that is rolled and pushed through two weld rollers.
  • Drawn-over-mandrel (DOM). With this method, a small piece of metal is placed in the tube in order to define its shape. Thanks to the piece of metal, the tube is given extra support in order to prevent unnecessary creases during drawing. With this method, tight tolerances and specifications can be achieved with the end result.

How quality is checked

In order to ensure that the end product meets certain specifications, a number of measures are taken. Raw materials can be inspected by use of a Spectro Analyzer, which instrument helps determine the level of purity of the material to be used.

A look at some of the quality control techniques used:

Quality Testing Equipment

A number of quality control testing equipments can be utilized to ensure that the quality of the end-product is as per set standards.

Such equipment includes:

  • Conductivity Meter
  • Universal Testing Machine
  • Optical Emission Spectrometer
  • Metallurgical Microscope
  • Hardness Tester Machine
  • Eddy Current Testing Machine
  • Hydraulic pressure testing machine.

Tests and Analysis

A number of tests and analysis can be utilized to ensure that the end-product meets set- standards. Some of these tests and analysis include:

  • Chemical composition analysis by use of a Spectro Analyser
  • Roughness of surface measure
  • Weather resistance testing
  • Radiation inspection
  • Coating mass test
  • Pencil hardness test
  • Tension test
  • Hardness test by use of a Universal Testing Machine
  • Spheroidal graphite analysis
  • Bend test
  • Flaring resistance
  • Transverse test
  • Impact test
  • Deformed bar test
  • Salt spray test
  • Cross cut test
  • Mechanical properties testing by use of a Microscope, Universal Testing Machine and a chemical lad for the case of a Mercurous Nitrate test.
  • Corrosion resistance analysis
  • Steel strand test
  • Fastener test
  • Micro-structure analysis
  • Fatigue test
  • Dimension measurements
  • Metallurgic examination
  • Macro-etching
  • Non-destructive testing inclusive of Remote visual inspection, ultrasonic testing, liquid penetration and x-rays.

Other quality control Techniques

Other quality control techniques that can be utilize in ensuring that the end product meets set standards include:

  • Inspection of the shell to ensure that the dimensions and appearance are as per set standards. Micrometer in addition to just visual analysis can be used in this instance.
  • Make use of a micro meter or measuring tape to ensure that the dimensions are the right wall thickness, length and straightness.
  • Ensure that the marking and packing are as per the customer’s requirement.