glossary

American Tube

Glossary of Terms


Age Hardening: An aging process that increases hardness and strength. Ordinarily ductility decreases. Usually rapid cooling or cold working.
Alloy: A metal containing two or more elements.
Annealing: The heating and cooling of steel to remove stresses, alter physical, mechanical and metallurgical properties, increase corrosion resistance, or to thermally treat steel prior to age hardening. Some scaling results from an oxide anneal.
ASME: American Society of Mechanical Engineers
ASTM: American Society for Testing Materials
As-Welded: Tubular products not subject to thermal treatment after welding.
Austenitic: The group of chromium-nickel stainless steels commonly known as 18-8 or 300 series. These steels are non-magnetic in the annealed condition and can only be hardened by cold-working.
Bright Annealing: Annealing in a controlled atmosphere (e.g., cracked ammonia, hydrogen, or vacuum) to prevent formation of oxides and scale. Eliminates the need for acid bath pickling and allows for natural passivation.
Burst Pressure: The internal pressure that will cause piece of tubing to fail.
Carbide: A Compound of metal and carbon. Chromium carbide at grain boundaries of austenitic stainless steels causes poor corrosion resistance. This carbide may result from welding or improper annealing.
Carbon Pickup or Carburization: Diffusion of carbon in the surface of steel when heated in the presence of a caronaceous compound. Condition may result from poor cleaning or from exposure to a carburizing atmosphere.
Cold Drawing: The mechanical work process of drawing tubular products through a hardened die while at room temperature. Usually done with a supporting mandrel (drawn over mandrel) to reduce the O.D., wall, or both.
Concentricity: As applied to tubular products, the center of the inside diameter is consistent with the center of the outside diameter. Welded, roll-formed tubing is inherently more concentric than seamless tubing because it is fabricated from precision rolled flat stock resulting in a more consistent wall thickness.
Descaling (molten salt): Subjecting oxide annealed austenitic and high allot steel to an oxidizing or reducing salt bath to produce more readily a scale-free surface when pickled in a subsequent step.
Destructive testing: Mechanical tests performed on a sample of tubing resulting in the sample's destruction. e.g.; tensile, yield, elongation, hardness, flare, flatten, reverse bend and burst.
Eccentricity: As applied to tubular products, the center of the inside diameter differs from the center of the outside diameter indicating wall variation. This is a problem associated with seamless tubing.
Full finished: Refers to tubular products in which the weld has been processed to produce uniform strength and dimensions, and subsequently annealed to obtain proper corrosion resistance.
Gas Tungsten Arc Welding (GTAW): An arc welding process that uses an arc between a non-consumable tungsten electrode and the weld pool (base metal of strip). A high quality full fusion weld is achieved using no filler metal. The GTAW process is also commonly referred to as Tungsten Inert Gas (TIG) welding.
Grain size: Statistical grain diameter in a random cross section. Austenite grain size is reported as the number of former austenite grains within a standardized area.
Hardness: Hardness of tubular products is measured by a destructive test performed on a standard Rockwell Penetrator and recorded on the Rockwell "B" scale. Hardness is inversely proportional to the temperature and duration of the annealing process. In general, as the hardness number increases, both tensile and yield strengths increase while elongation (ductility) decreases.
Heat Number: A number assigned to a particular melt of material for identification and product traceability.
Hydrostatic testing: A nondestructive test procedure used to check a length of tubing for holes, cracks, and porosity. Tubing is filled with water at a high pressure for a specified period of time to check for leaks.
Inclusions
Non-metallic materials (usually oxides, sulfides and silicates) found within a metal matrix.
Line Marking
Information printed with an inert ink on the outside diameter of a tube. Data includes, but is not limited to, ASTM spec number, material heat number, tubing size, wall thickness and manufacturer name. Ensures full product traceability.
Manipulation tests: see "Destructive testing"
Mean Coefficient of Thermal Expansion: A number multiplied by the length of tubing (in inches) and the rise in temperature (in °F) to calculate how long a tube will expand during heating.
Mechanical properties: Characteristics of a material in response to externally applied forces. e.g.; tensile strength, yield strength and elongation hardness.
Modulus of Elasticity: Stress per unit strain, measured in psi. The higher the number, the more rigid the item will be for a given load.
O.D.: The outside diameter of a tubular product.
Orbital Weld: A circumferential, full fusion weld used to join together two lengths of tubing. It is a GTAW welding process. Usually to join coiled lengths.
Ovality: The difference between the maximum and minimum diameters of a tubular section.
Passivation: A protective layer of oxides on the surface of a metal which resists corrosion. This passive oxide layer is the primary reason stainless steels have such excellent corrosion resistance.
Pickling: Chemical or electro-chemical removal of surface oxides.
Pressure test: Subjecting tubular products to specified hydraulic or pneumatic internal pressure to detect defects or weaknesses in the tube wall.
Process Anneal: Annealing close to, but below, the eutectoid temperature.
Sinking (sink drawing): A cold finishing operation to obtain exactly the desired diameter and/or to improve mechanical properties. Performed by pulling a tube through a hardened die without using an interior tool (mandrel).
Straightness tolerance (camber): Maximum deviation, or bow, within a specified length. Usual method to determine straightness is to use a straight edge and a dial indicator or a flat plate and feeler gauges.