Technical Information
Products and Information
BS EN 10305-03/05
DIN2394/5 St37.2
KM BS 6323 Part 5 ERW1 KM
Technical Information and Terminology
Formula for working out the weight of a steel tube:
OD in MM minus WT in mm times WT in MM times 0.0246615 = kilogram per metre. For shapes divide the circumference by 3.1428
For example:
19OD x 1.5mm tube
19-1.5 =17.5
x1.5 = 26.25
x0.0246615 = 0.64kg/mtr. Therefore 500mtrs weighs 320KGs
'Yield stress' (strength) Re .... The stress (load divided by original area of cross-section of a test piece) at which, in a tensile test, elongation occurs without increase of load. Or put simply, the point where it will not return to its original shape .
'Tensile strength' Rm...
The maximum load reached in a tensile test divided by the original cross-sectional area of the gauge length portion of the test piece. Also termed maximum strength or ultimate tensile stress.
Or, put simply, the point at which it will break.
Elongation....
The increasing length of a test piece when stressed. The elongation at fracture is usually expressed as a percentage of the original value.
Random Length
The mill length, usually 6.1m.
Multiple Length
A length made for a specific shorter length - important to take into account the cutting blade thickness and the holding distance needed for the machine, doing the cutting, this is normally the gap between the blade and the vice. These figures need to be added to the multiples of the cut lengths required.
Swaging
An operation designed to reduce the end of a cut tube.
Swelling Bulging
Increasing the diameter of a tube end for a short distance. Popular in boiler tubes.
Eccentricity
The non-coincidence of the centres of the bore and outside diameter of a tube, resulting in the tube thickness being greater on one side than the other.
Gauge
Wall thickness, normally SWG- standard wire gauge.
Ovality
Lack of roundness on the outside circumference of a tube, beyond the permitted tolerance.
Roll Marks
An outside surface defect occurring periodically along the tube length, caused through some imperfection on a roll during manufacture.
Reeling
The straightening of tubes by passing them through inclined rolls.
Scores
Longitudinal marks transverse the surface finish, other than that expected during manufacture. Usually meaning they cannot be covered by normal finishing processes, like powder coating.
Heat treatment
This is a process in which metal, in the solid state, is subjected to one or more temperature cycles to confer certain desired properties. Heating for the sole purpose of hot working is not included in this term.
Basic metallurgical principals are important here. Steel is essentially an alloy of iron and carbon, the latter as iron carbide. A change in the crystal structure of the iron (allotropy) and the form of the carbide present can be brought about by thermal treatment. In this context there are two significant temperatures change points, for steel containing up to 0.83% carbon, which define the upper and lower limits of the transformation range.
The lower critical limit temperature is 723°C and remains unchanged regardless of the carbon content. The upper critical limit of 910°C ranges from 0.01% carbon, to the lower limit with .080% carbon. The upper limit falls as the carbon content increases. Alloying elements such as nickel, chromium, molybdenum, etc, can have a significant effect on the critical limits but the basic principle remains the same.
Annealing
Heating to and holding at a suitable temperature and cooling at a suitable rate, for such purposes as:-
- Inducing softness
- Improving machinability
- Improving cold working properties
- Obtaining a desired structure
- Removing stresses
Bright annealing
Heat treatment in a controlled atmosphere such that the surface remains unoxidised.
Stress relieving
Heating to and holding at a temperature for the sole purpose of relieving internal stresses. Most annealing processes will relieve the structure. Essentially the molecular structure becomes aligned - the molecules line up, as opposed to when stressed they agitate and become jumbled making them harder to work.
Work hardening
Just as heat treatment will affect the properties of a steel tube so will working the tube. That is to say when making a tube the properties will alter according to the pressure and work done to achieve a given size. For instance 12 x 1.5 will work harden more, when being made, than 50 x 1.5, simply because there is proportionally more energy transferred to the smaller ratio tube. There is a correlation between the OD and WT ratio, where the ratio is determined by dividing the WT into the OD, so that 12 x 1.5 has a ratio of 8:1 and 50 x 1.5 has a ratio of 33.33:1.
Mechanical tube
A term applied broadly to tubes used for engineering purposes as distinct from those used for the conveyance of liquid.
HPL - Hydraulic Pipe Line
A tube used for the conveyance of a liquid under pressure in connection with hydraulic machinery
ERW Tube
Electric Resistance Welded is a tube made from flat strip, formed and subjected to a radio frequency causing the edges to heat to a temperature that allows it to be welded. The weld is achieved by pressing the edges together, the outer weld is removed and sometimes the internal weld (fin) can also be cut. The welding is sometimes referred to as forge welding, which is, as it sounds, an archaic term.
Cylinder tube
A tube used in hydraulic or pneumatic pressure applications, having an inside surface not injurious to a cup plunger or piston.
Boiler tube
Tubes which form part of the heating surface of a boiler. The tubes may contain water and be surrounded by furnace gases, or may act as a flues and be surrounded by water.
Condenser tubes
Tubes used in the conversion of a vapour into a cooling.
Smooth bore tube
A cold drawn tube having a bore finish within certain prescribed limits of surface roughness.
Hollow
A tube from which a cold drawn tube is manufactured.
Mandrel bend
A bend on a tube where the shape is supported by a machined piece of metal made to the same shape and dimensions as the bore.
Crush bend
A tube bend where the shape is intentionally deformed to create a stronger bend.
Press bend
A tube bend where there is only external contact with the forming tools.
Flowdrill
A process where a conical shape bit is spun at high revs to create a friction so as to melt the parent metal, creating a hole and a well of steel that can then be threaded. It is also possible to pierce a tube and thread the resultant hole, but usually only on wall thickness above 1.5mm.