Steel Tubing Glossary of Terms
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.
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
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 are the mimimum and maximum limites of chemical elements as
established by ASTM and SAE specifications.
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.
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
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 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
Finish refers to the type of surface and end condition desired in the finished product to
suit the customer's need.
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 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" 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.
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.
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.
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
A mechanical property of steel that measures the resistance to indentation. Hardness is
related to the maximum strength of steel.
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 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.
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 refers to the inside diameter of the tubing. It is specified in inches and decimals of an
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 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
Abbreviation for the Metals Service Center Institute.
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.
Testing methods of detecting defects without destroying or permanently changing the
material being tested.
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 is an abbreviation for outside diameter. It is expressed in inches, decimals of an
inch and in metric.
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 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
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.
Defined as the oxide of iron that is formed on the surface of steel after heating.
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 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
Abbreviation for the Steel Tube Institute.
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.
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.
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 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 is a steel finish that utilizes elements such as copper, chromium,
nickel and silicon to enhance the protection and resistance to atmospheric corrosion.
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
Yield strength is the stress at which steel begins to exhibit a specified deviation from