Tubing and pipe glossary of terms

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The controlled process of heating and cooling a metal to achieve a reduction in hardness, remove stress, and to homogenize the material.

ASM (American Society for Materials International)
A professional society of Material Scientists and Engineers dedicated to the collection and distribution of information about materials and manufacturing processes.

ASME (American Society of Mechanical Engineers)
An organization of engineers dedicated to the preparation of design code requirements, and material and testing standards. Adopts, sometimes with minor changes, specifications prepared by ASTM. The adopted specifications are those approved for use under the ASME Boiler and Pressure Code and are published by ASME in Section II of the ASME Code. The ASME specifications have the letter “S” preceding the “A” or the “B”, of the ASTM specifications. The “SA” series are for iron base materials, while the “SB” series are for other materials such as nickel base, copper, etc.

ASTM (American Society for Testing and Materials)
A body of industry professionals involved in writing universally accepted steel material and test specifications and standards. The "A" series of material specifications are for iron base materials, while the "B" series are for other materials such as nickel base, copper, etc.

A non-magnetic metallurgical phase having a face-centered cubic crystalline structure. Except for steel compositions having at least 6% nickel, austenite is typically only present at temperatures above 1333°F (723°C).

These grades of stainless steels (300 Series plus some 200) have chromium (roughly 18% to 30%) and nickel (roughly 6% to 20%) as their major alloying additions. They have excellent ductility and formability, at all temperatures, excellent corrosion resistance and good weldability. In the annealed condition they are nonmagnetic. Some have the ability to be hardened by cold rolling as a final step. These grades are usually non-magnetic and are used for applications requiring good general corrosion resistance such as food processing, chemical processing, kitchen utensils, pots and pans, brewery tanks, sinks, wheel covers and hypodermic needles.

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A test for determining relative soundness and ductility of a metal to be formed. The specimen is bent over a specified diameter through a specified angle. In welded tubing the weld is of primary interest.

A heat treat process performed in a carefully controlled furnace atmosphere resulting in a clean, smooth, scale free metal surface. During typical annealing, the heated steel combines with oxygen in the air to form an oxide layer on the steels surface. In bright annealing, the steel is heated in a furnace filled with gases, such as hydrogen or nitrogen, or in a vacuum, to prevent oxide scale formation. The material comes out of the bright anneal furnace with the same surface as it had when it went into the furnace. The process eliminates the need for the old fashioned acid bath pickling operations.

The internal pressure that will cause a piece of tubing to fail by exceeding the plastic limit and tensile strength of the material from which the tube is fabricated.

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The process of pulling a tube through a carbide die to reduce the diameter of the tube. Small tubes with very high thickness-to-diameter ratios are commonly produced this way in long lengths. The sinking of the tube is done at room temperature (i.e.: “Cold”).

Used to describe tubing where the center of its inside diameter is consistent with the center of its outside diameter resulting in no variation of wall thickness. By virtue of the fact that welded tubing is fabricated from precision rolled flat stock, concentricity is inherent with a roll-formed, welded tube.

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Removal of a small ridge of metal formed by upset during a machining or cutting operation.

Stainless Steels exhibiting both austenitic and ferritic, phases and characteristics.

Any of the mechanical tests performed on an expendable sample of tubing to check physical properties. These tests include: tensile, yield, elongation, hardness, flare, flattening, bend and burst.

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Opposite of concentricity, resulting in variations of wall thickness.

A nondestructive testing procedure which is a continuous process performed on the tubular products during fabrication and in final inspection. It is by nature an electrical test that utilizes fluctuations in magnetic field strength to check tubing (against a calibrated standard) for possible defects such as holes, cracks, gouges, etc. on both inside and outside surfaces of the tube. All eddy current testing at RathGibson is done in accordance with ASTM-E 426.

An electro-chemical method of surface finish enhancement in which the metal to be polished is exposed to a suitable electrolyte, typically an acid solution, while carefully controlled current is passed between the object and a cathode. The object to be polished is the anode, and polishing is accomplished through the uniform removal of surface metal that goes into solution. Surface finish roughness of less than 0.000,010-inch (10 microinch) is attainable.

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A metallurgical phase of iron having a body-centered cubic crystalline structure. It is soft, magnetic, and less susceptible to certain corrosion cracking than austenite.

A calculated value indicating the relative ability of a particular chemical composition of steel to form ferrite upon solidification from the molten state. The higher the ferrite number the higher the percent of ferrite formed. Several different ferrite number formulas have been developed and should not be interchanged.

A magnetic grade of stainless steel having a microstructure consisting of ferrite, including some of the 200 and 400 series stainless steels. Hardness can be increased slightly by cold work, but not by heat treatment. At lower temperatures ductility and formability is significantly less than that of austenitic grades. As the only major alloying element is chromium (10 to 30 per cent depending on specific grade) these steels are relatively inexpensive to produce and are common in automotive exhaust and ornamental applications.

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An arc welding process that uses an arc between a tungsten electrode (nonconsumable) and the weld pool (base metal of strip). A high quality full fusion weld is achieved. The process can be performed with or without the addition of filler material. The GTAW process is also commonly referred to as Tungsten Inert Gas (TIG) welding.

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Resistance to deformation or indentation. Materials with little resistance are called soft; and those with high resistance are called hard. Finer grained structures are harder than larger grained structures. Measured in steel by scientific instruments as follows: Brinell machine for sizes over 1/2" in diameter or thickness. Based on measurement of the diameter of the indentation of a standard size ball under a standard applied load.

Rockwell machine for sizes under 1/2" in diameter or thickness. Based on a measurement of the depth of penetration of a standard indentor under a standard applied load.

“B” scale - for soft materials such as brass, stainless steel (1/8" ball @ 100 kg load)

“T” scale - for very thin (<0.040" thick) soft materials that normally use the "B" scale (1/16" ball @ 15, 30 or 45 kg load)

“C” scale - for harder materials such as high strength steel, tool steel, duplex stainless steel, martensitic and precipitation hardening stainless steel (diamond @ 150 kg load)

“N” scale - for very thin (<0.040") harder materials that normally use the "C" scale (diamond @ 15, 30 or 45 kg load)

The interest in hardness is because hardness correlates well with strength; with harder materials being stronger.

A lot of steel produced by a furnace with one chemical composition. Steel melting is a batch process and each batch is a heat. Also known as a melt of steel. In austenitic stainless steels a heat is typically about 200,000 pounds of material, and will yield approximately 8 coils of 25,000 pounds each. Nickel base materials are typically melted in heats of 10,000 to 50,000 pounds, yielding 2 to 5 coils of 5,000 to 25,000 pounds each.

An identifying number assigned to the product of one melting (e.g.: 721299).

A corrosion test for evaluating intergranular corrosion resistance by boiling in refluxed 65% nitric acid for five consecutive 48-hour periods, each period starting with fresh acid. The weight of metal lost is converted into loss in ipy (inches per year) or ipm (inches per month). ASTM-A262 Practice C.

A nondestructive test procedure that checks for holes, cracks or porosity. Tubing is pressurized internally with water to a high pressure, but does not exceed material yield strength.

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Inside diameter of a tubular product. It is also known as the opening or bore of a tube or pipe.

Corrosion that occurs at the grain boundaries in austenitic stainless steels that have been heated to and held at temperatures between 850° F and 1450° F. Slow cooling through this range can also result in sensitization to intergranular corrosion. Usually caused by precipitation of chrome carbides.

ISO (International Organization for Standardization)
Prepares specifications. Both Canada and the U.S.A. are ISO members and participate in the ISO specification development.


A fusion joining process that produces coalescence of materials with the heat obtained from a concentrated beam of coherent, monochromatic light impinging on the joint to be welded. Generally an autogenous weld with no filler metal added.

A continuous strip of information that is printed with an inert ink along the longitudinal surface of the tube after final inspection. This data includes ASTM spec number, material identification, size and wall thickness, as well as a heat number identity. Full traceability is possible with any line marked product.

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This is the amount that a material will ‘grow’ in size when subjected to a temperature rise. It is measured in inches/inch/°F. This number multiplied by the length of the tubing (in inches) and by the temperature rise (in °F) indicates how much the tube length will expand (in inches). If the temperature decreases, the tube will shrink by a similar amount.

The process starts with the simultaneous deburring of both ends of a tube. A pneumatic polishing head, fitted with an abrasive material, rotates within the tube for many cycles to achieve the desired interior surface finish. Any residue is removed by blowing a clean wipe through the tube before visual inspection. Ends of the tube are capped to protect the interior during the mechanical polishing process. Two heads spin the tube before it hits the first OD polishing head. Lubricant and rough grit compose the wet polish, which is recirculated and filtered. The tube goes through eight polishing heads, with the grit getting successively finer. As the tube exits the polishing area, air blows off any residual lubricant. The tube is then visually inspected for polishing on the exterior and residuals in the interior. Should the tube pass this last visual inspection, both ends are vinyl capped, and the tube is line marked with its alloy, size, weld, and manufacturer to ensure complete traceability. For added protection, the tube is heat sealed in a poly-sleeve.

A ratio of stress to strain. Used in engineering calculations to determine rigidity and deflections. The higher the number, the more rigid the item will be for a given load. The units are in pounds per square inch (psi).

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Abbreviation for the Nickel Development Institute. A group of engineering professionals dedicated to the distribution of information regarding the selection and application of nickel alloyed materials.

See “Eddy Current Testing” or “Hydrostatic Testing”.

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Outside diameter of a tubular product.

A circumferential, full fusion butt or girth weld used to join together two lengths of tubing. It is a GTAW welding process similar in nature to the longitudinal weld seam of a welded tubular product.

A quantitative measurement of how ‘round’ a tube is by comparing width to height. Limits are specified on the appropriate ASTM specification of a product.

An electro-chemical reaction in which oxygen attacks a metal surface to form a metallic oxide, such as rust or the protective layer on stainless steel.

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A protective layer of oxides on the surface of a metal, which resists corrosion. This passive oxide layer is the chief reason why stainless steels have such good corrosion resistant properties. It is a natural phenomenon, but can be accelerated by special passivating solutions that can be applied to tubular products by an optional process.

An instrument that quantitatively measures surface roughness and reports height and/or depth of surface ridges.

Common engineering abbreviation for pounds per square inch. A measurement of stress in a material.

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(1) Formation of a new, strain-free grain structure from that existing in cold worked metal, usually accomplished by heating (solution annealing of austenitic stainless steels). (2) The change from one crystal structure to another, as occurs when heating or cooling through a critical temperature. As in the change of an as-welded dendritic structure to an equi-axed grain structure, similar to that of the parent material.

A measure of the optical properties or “brightness” of a metallic surface expressed in terms of the percentage of the impinging illumination that is reflected back from that surface.

An expression of measured surface roughness or texture, typically, of a polished or machined metal surface. The arithmetic average value of the departure (peaks and valleys) of a surface profile from the centerline throughout the sampling length, generally expressed in micro-inch (0.000,001-inch) or micro-meter (or micron) (0.0003937-inch) units.

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A means of indicating the wall thickness of pipe sizes, as set forth in ASME B36.1 and ASTM A530 and B775. Commonly available pipe schedules are Schedules 5, 10, 20, 40, and 80. The actual wall thickness of a schedule number varies with the nominal pipe size or diameter (e.g.: 0.5" Sch 40 = 0.109" while 2" Sch 40 = 0.154"). A higher number schedule indicates a thicker wall for a particular pipe diameter.

Tubular product that is made by piercing or hot extrusion to form the tube hollows. Further reduction of the tube hollows is accomplished by cold drawing or tube reducing to the final finish and size. Initial steel billet or ingot is cast.

The tendency of a material deformed under load to return to its original shape when the load is removed, like a rubber band returning to its unstretched condition when an applied load is released. Springback occurs in the elastic deformation regime, or at loads less than the yield strength of the material.

The broad classification of iron-based alloys (50% minimum iron) containing at least 10% chromium that are known for their excellent corrosion and heat resistance. Other elements are also added to form alloys for special purposes, in addition to the corrosion resistance imparted by chromium. Some of these elements are: nickel for increased corrosion resistance, ductility and workability; molybdenum for increased corrosion resistance, particularly resistance to pitting, increased creep strength and high temperature strength; columbium and titanium for stabilization; sulfur and selenium for improved machinability.

Catastrophic failure by generally transgranular cracking occurring in stainless steels and other metals. It is caused by combined action of a corrosive environment and stress, often without outward appearance of general corrosion attack.

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A short form of “ultimate tensile strength”. The maximum load per unit area that a material is capable of withstanding before it fails (pulls apart). Units are in psi.

A procedure used to determine the load at which a material will begin to plastically deform (the tensile yield strength) and ultimately at which it will break (the ultimate tensile strength). Resulting test values are a ratio of applied load (pounds) to cross-sectional area of the test sample (square inches) and are expressed in units of pounds per square inch (psi) or in metric units of megaPascals (MPa).

TIG (Tungsten Inert Gas)
A welding process that uses a non-consumable tungsten electrode to provide an electric arc to melt a work piece. Inert gases are used to shield the arc and the weld puddle to prevent oxidation during cooling. Used for heat exchanger, condenser and sanitary tubing.

OD = Outside Diameter ID = Inside Diameter

Wall thickness or gauge

All tube dimensions are specific; pipe dimensions are nominal.

Specific – actual measurement in inches

Nominal – theoretical or stated value of a dimension

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The stress in pounds per square inch (psi) that causes the material to fracture.

The scanning of material with an ultrasonic beam, during which reflections from faults in the material can be detected: a powerful nondestructive test method.

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A corrosion test developed for the black liquor industries (pulp/paper, sugar refining) to detect susceptibility of stainless steel weldments to attack by boiling hydrochloric acid cleaning solutions. Test results are reported as a ratio of the change in thickness of the weld to the change in thickness of the base material. A ratio of 1.0:1 indicates no difference between weld and base metal. A ratio of 1.25:1 indicates that the weld thickness changed by 25% more than the base material did.

Tubular products which are roll formed and then joined continuously along a longitudinal seam by a material fusion process. The process employed at RathGibson is Gas Tungsten Arc Welding (GTAW). See "Gas Tungsten Arc Welding" and "Laser Beam Welding" (LBW).

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The load per unit area that a material can withstand before permanent deformation (nonelastic) occurs. It is conventionally determined by a 0.2% offset from the modulus slope on a stress/strain diagram. Units are in psi and referenced to 0.2% offset in most literature.