Steel Tubing Glossary of Terms
A/uminized
Aluminized steel is steel that has been coated on both sides with an aluminum silicon alloy. Aluminized steel has a unique combination of properties possessed neither by carbon steel nor by aluminum alone. Aluminized steel shows a better behavior against corrosion and is used in various application where heat resistance is critical.
Carbon Steel
Steel is classified as carbon steel when its properties are defined by the various percentage of carbon without substantial amounts of other alloying elements. As carbon content increases, the steel becomes harder and stronger while the ductility of the steel decreases.
Charpy Test
A Charpy test, also known as the Charpy v-notch test, is a high strain test that determines the amount of energy absorbed by a sample of material during fracture. A free swinging pendulum is allowed to strike and break a notched sample. The position of the pendulum before and after the pendulum swings is compared. The energy absorbed is a measure of the the impact strength or notch toughness. ASTM standard E23 outlines the testing requirements.
Chemical Properties
Chemical properties are the mimimum and maximum limites of chemical elements as established by ASTM and SAE specifications.
Coil
Steel coils are sheets of steel that have been wound up by a steel mill. Large coils are slit or cut down to smaller widths desired in order to produce tubing. Once unwound, the flat coil is then formed to produce the mechanical tubing.
Cold Rolled
Colled rolled steel is hot rolled sheet that has been cold reduced. Cold rolled steel provides tighter wall thickness tolerances and better surface condition than hot rolled steel.
Crush Test
A test performed that exerts compressive force that is perpendicular to the diameter of the tube that is placed on end.
Drawn Over Mandrel (DOM)
A secondary cold working process done to ERW tubing in order to obtain a special shape or tighter OD, ID, or wall thickness tolerances. An intermediate and less costly option to DOM would be to order ERW tubing to tighter than standard A513 tolerances.
Eddy Current Testing
Eddy Current testing is a non-destructive testing method that utilizes an eddy current flow to detect a discontinuity in the weld area of the tubing.
Elongation
Elongation is the amount of permanent extension in the vicinity of the fracture in a tension test. It is expressed as a percentage of the original gauge length.
ERW (Electric Resistance Weld)
Electric resistance weld tubing (ERW) is a method of tubing production where slit coils of steel are put through a gradual cold forming operation until the two edges of the steel are joined together in a tubular form. The heat for the continuous weld is generated at the seam by the resistance to the flow of electric current applied through an induction coil.
Finish
Finish refers to the type of surface and end condition desired in the finished product to suit the customer's need.
Flare Test
A destructive test performed that tests the weld suitability of a piece of tube when it is expanded over a cone at various degrees of expansion.
Flash Control
Flash control refers to the different limits that the flash left from the ID weld bead can be controlled to during the ERW tube production process. For example, flash control to .015" means that the maximum ID weld bead that can remain is .015". Flash control requirements vary by end use application.
Flash In
"Flash in" refers to when the flash from the weld is left on the inside of the tubing and is not removed or controlled during the ERW tube production process. If flash is required or not, please make mention of that at the time of quotation and order placement.
Flattening Test
A destructive test performed in the tube production process where a sample tube is flattened to a specified height. The weld is positioned at a predetermined location. Examination is made during the test for signs of cracking.
Galvanized
Refers to the thin layer of zinc finish that is applied to steel. Galvanized steel is used in applications where rust resistance is needed. It is identified by a crystalization patttern on the surface called "spangle". Galvanized tubing can be supplied in two ways: "pregalvanized" meaning that the steel is galvanized at the steel mill or as "hot-dipped galvanized" meaning that the tubing is produced from a hot rolled steel and then hot dipped after welding.
Gauge
A measurement of wall thickness of the steel. The Birmingham Wire Gauge terminology is commonly used in the tubing industry. For each gauge, there is a corresponding wall thickness to match that. For example an 18 gauge can also be referred to .049" wall thickness.
Hardness
A mechanical property of steel that measures the resistance to indentation. Hardness is related to the maximum strength of steel.
Hardness Test
A test taken in order to measure the hardness (resistance to penetration) of steel.
High Strength Low Alloy
Low alloy steels in which the inclusion of moderate amounts of alloying elements other than carbon lead to higher mechanical properties.
Hot Rolled
Hot rolled steel is steel that while it is being formed or rolled is heated red-hot. As the steel cools in the open air, the surface oxidizes creating a blue grey scale finish. Wall thickness tolerances within the coil will not be as uniform or as tight as steel produced as cold rolled.
Hydrostatic Testing
A pressurized test in which a liquid, normally water, is placed in the pipe or tube at the required pressure to ensure that it will not leak or be damaged.
ID
ID refers to the inside diameter of the tubing. It is specified in inches and decimals of an inch.
Mechanical Properties
The mechanical properties of steel show the elastic and inelastic reaction of the steel when force is applied to it. Yield strength, tensile strength and elasticity are common mechanical tests performed. Also referred to physical properties.
Mechanical Tubing
Mechanical tubing is used for a variety of mechanical purposes and is produced to meet specific end use requirements, specifications, tolerances and chemistries. Closer dimensional tolerances and chemistries allow for more uniformity than standard pipe for the end user.
Minimum Wall Thickness
The lowest value that steel can be measured at in order to ensure that it meets the corresponding ASTM specification for the coil or tube or customer requirement specified. It can be calculated by subtracting the minus tolerances from the nominal wall thickness.
MSCI
Abbreviation for the Metals Service Center Institute.
NASPD
Abbreviation for the National Association of Steel Pipe Distributors.
Nominal Wall Thickness
The theoretical or stated single value given to the gauge or wall thickness of steel.
Non-Destructive Testing
Testing methods of detecting defects without destroying or permanently changing the material being tested.
Normalizing
The heat treatment of steel where a tube or weld seam of the tube is heated above the critical range and then cooled in still air. The crystal structure is refined and with a more consistent strength. Internal stresses are removed in the steel.
OD
OD is an abbreviation for outside diameter. It is expressed in inches, decimals of an inch and in metric.
Oiling
The application of an oil or coating to the finished tube to help improve the shelf life of the tube and to slow down rusting. Depending upon the end use of the tubing, oiling may or may not be required.
Ovality
Ovality is the difference between the maximum and minimum diameters of any one section of a round tube as measured.
Pickled & Oiled
Often referred to as HR P&O, pickled & oiled is a finish where hot rolled coil is descaled of oxide film or scale by either a chemical method, mechanical method, or a combination of both and then oiled to help prevent corrosion after descaling. Pickled & oiled steel offers a cleaner surface than hot rolled steel, making it an attractive alternative to cold rolled steel in terms of cost if wall thickness tolerances are not as critical.
Pipe
Pipe is a round hollow form of steel produced to a nominal pipe size (NPS) and used in conjunction with the term "schedule" that defines the wall thickness. It is mainly used to convey liquids, gasses and other substances. It is important to distinguish between the terms pipe and tube. Tube is identifed by the OD size and wall thickness. A 2" NPS schedule 40 "pipe" size would be described as 2.375" OD x .156" wall in a "tube" size.
Reverse Flattening Test
A reverse flattening test involves taking a sample of tubing at a specified length and splitting is lonitudinally at 90 degrees on each side of the weld. The sample is opened and flattened with the weld area at the point of maximum bend. It is used primarily to detect lack of weld penetration.
Scale
Defined as the oxide of iron that is formed on the surface of steel after heating.
Slitting
Slitting is the continuous longitudinal splitting of a wider coil into two or more separate strips by rotary knifes mounted on a rotating arbor..
Stainless
Stainless steel is a steel alloy that contains more than 10 percent chromium. Stainless steel is known for not staining, corroding or rusting as easily as carbon steel. There are various different grades of stainless steel including stainless 304, 316, 409, 410 and 416.
STI
Abbreviation for the Steel Tube Institute.
Structural Tubing
Tubing that is used primarily for structural applications. Strength requirements help dictate the type of steel to be used for the particular application.
Submerged Arc Weld (SAW)
SAW is a type of arc welding in which a fluxa special welding materialis used to protect the weld area from the effects of the surrounding air and to improve the conditions for formation of the weld. A weld bead up to .250" of an inch is left on the OD of the tube.
Steel Tubing Glossary of Terms
A/uminized
Aluminized steel is steel that has been coated on both sides with an aluminum silicon alloy. Aluminized steel has a unique combination of properties possessed neither by carbon steel nor by aluminum alone. Aluminized steel shows a better behavior against corrosion and is used in various application where heat resistance is critical.
Tensile Strength
Tensile strength - also referred to as "ultimate strength" - is a measure of the ability of steel to withstand a longitudinal stress, expressed as the greatest stress that the steel can stand without breaking.
Tolerances
The allowable difference in measurements from a desired value between what the customer requests or what an ASTM specification calls out for. Examples of common tubing tolerances include OD, ID, wall thickness, chemical and length tolerances.
Tubing
Tubing is a non-standardized hollow shaped product manufactured to specific dimensional, chemical and mechanical properties. It is important to distinguish between the terms pipe and tubing. A tube is identifed by the OD size and wall thickness while a pipe is produced to nominal specifications. A 2" NPS schedule 40 "pipe" size would be described as 2.375" OD x .156" wall in a "tube" size.
Weathering Steel
Weathering steel is a steel finish that utilizes elements such as copper, chromium, nickel and silicon to enhance the protection and resistance to atmospheric corrosion.
Weld Bead
The built up portion of a weld, formed either from the parent material of the tube with electric resistance welded (ERW) tubing or from a filler metal in the case of submerged arc welded (SAW) tubing. The OD welded bead is standardly removed in the ERW tube making process while the ID weld bead may be left in (flash in) or controlled to different tolerances (flash controlled) as required by the customer requirement or end use application.
Yield Strength
Yield strength is the stress at which steel begins to exhibit a specified deviation from inelastic strain.
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