Technical Terms For Tubing
Please note that the definitions below are provided for reference purposes only.
- Annealing - A general term referring to the thermal treatment process involving heating and cooling, usually applied to change mechanical or physical properties, produce a desired microstructure.
- Annealing (Normalizing) - An annealing process in which a steel is heated to a temperature that is above the upper transformation range and then cooled in air. The tube surface has a black or blue color due to oxidation at elevated temperature. Tubing can be heated above the upper transformation temperature and cooled in a reducing atmosphere and maintain a bright surface, as in bright annealing above.
- Annealing (Bright Annealing) - An annealing process usually carried out in a controlled atmosphere furnace using a reducing atmosphere to achieve desired mechanical properties with minimum surface oxidation. The tube surface is relatively bright.
- Carbon Steel Tube - Steel tube containing only residual quantities of elements other than carbon and manganese. Typical industrial AISI designate steel grades include 1006 and 1008. The grade designation indicates the nominal percent carbon i.e. 1006 nominally has .06% carbon, 1008 nominally has .08% carbon, etc. Grades 1006 and 1008 are the most common grades specified for low carbon welded seam tubing.
- Dimensions of Tubing - A round tube section has three dimensions, any two of which may be measured. The three dimensions are outside diameter (OD), inside diameter (ID), and wall thickness (t or W). Nominal as applied to any of these dimensions refers to the theoretical or stated single value of that dimension. The dimensions ordinarily specified by the customer are termed "nominal". Maximum and Minimum referring to the greatest and least values of any dimension. Average dimensions are those secured by averaging a series of micrometer readings. (Welded tubing is generally specified by the outside diameter and wall thickness. Cold drawn tubing may be specified by outside and inside diameter.)
- Total Elongation - The total amount of permanent extension in the vicinity of the fracture in the tensile test to failure; usually expressed as a percentage of the original gauge length.
- Fatigue - The tendency for a metal to break at a point that is considerably below the ultimate tensile strength due to the conditions of repeated cyclic stressing considerably below the ultimate tensile strength.
- Formability - The ease with which a metal can be shaped through plastic deformation. Evaluation of the formability of a metal involves measurement of strength, ductility, and the amount of deformation required to cause fracture.
- Hardness - Resistance of metal to plastic deformation. Various surface hardness tests such as Rockwell may be used. For thin walled tubing, superficial Rockwell testing is generally specified and testing performed on the inside surface of the tubing without correction for sample shape. The hardness of tubing is a result of the steel chemistry, the amount of cold-work performed on the tubing, annealing time and temperature, the degree of quench, and age hardening that occurs following production.
- Heat-Affected Zone (HAZ) - The adjacent portions of the base metal that were not melted during welding, but whose microstructure and mechanical properties were altered by the heat of welding.
- High-Strength Low-Alloy (HSLA) Steels - Steels designed to provide better mechanical properties and/or greater resistance to atmospheric corrosion than conventional carbon steels. They are not considered to be alloy steels in the normal sense because they are designed to meet specific mechanical properties rather than a chemical composition.
Typical HSLA steels have minimum yield strengths 40 ksi, 50 ksi, 60 ksi, 70 ksi or 80 ksi.
The chemical composition of the specific HSLA steel may vary for different product thickness to meet mechanical property requirements. The HSLA steels have low carbon contents (0.05 to ~0.20% C) in order to produce adequate formability and weldability. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium and titanium are used in various combinations.
- Non-Conformance – Any failure to meet a written specification for dimension or surface appearance.
- Inclusion - A physical or mechanical discontinuity occurring within a metal product, usually consisting of nonmetallic foreign material. Inclusions are often capable of transmitting some structural stresses and energy fields, but to a noticeably different degree than from the parent material. The foreign particles are usually compounds, such as oxides, sulfides, silicates or combination of these.
- Mechanical Properties - The properties of a material that reveal its elastic and inelastic behavior when force is applied, thereby indicating its suitability for mechanical applications; for example tensile strength, yield strength, elongation, hardness, and fatigue limit. Tubing’s mechanical properties are typically produced to an ASTM, SAE or customer-specific specification.
- Physical Properties - Properties of a material that are relatively insensitive to structure and can be measured without the application of force; for example, density, electrical conductivity, coefficient of thermal expansion, magnetic permeability.
- Tensile Strength - The value obtained by dividing the maximum load observed during tensile straining until breakage occurs by the specimen cross-sectional area before straining. Also called "ultimate strength".
- Tubing - A non-standardized hollow shaped product with a relatively uniform wall thickness, generally round and manufactured to specified requirements or dimensions. Chemical composition, mechanical properties and other physical characteristics may be required for applications in automotive, mechanical, pressure or structural uses. It is generally specified to two dimensions, i.e., outside diameter (OD) and wall, inside diameter (ID) and wall, or OD and ID.
- Yield Strength - The stress at which a material exhibits a specified limiting deviation from proportionality of stress to strain. An offset of 0.2 %. is used for steel.