Glossary of tube terms

ASME (American Society of Mechanical Engineers)
An organisation of engineers dedicated to the preparation of design code requirements, and material and testing standards.

ASTM (American Society of Testing and Materials)
A body of industry professionals involved in writing universally accepted steel material and test specifications and standards.

As-drawn tube
Any tube in any temper other than annealed or heat treated.

Alloy Surcharge
The producer’s selling price plus a surcharge added to offset the increasing costs of raw materials caused by increasing alloy prices, normally based on the LME, London Metal Exchange.

Annealing (Solution Annealing)
The controlled process of heating and cooling a tube to achieve a reduction in hardness, it relieves stresses that have built up during cold working and insures maximum corrosion resistance. Annealing can produce scale on the surface that must be removed.

Austenitic Stainless Steel
Non-magnetic stainless steels ( 300 series ) that contain chromium (18-30%) & nickel (6-20%) as their major alloying additions. Sufficient to develop and retain the austenitic phase at room temperature. Austenitic stainless steels are the most widely used category of stainless steel.

Bend Tests
Tests used to assess the ductility and malleability of stainless steel tubes subjected to bending.

Bright Annealing
A heat treat process performed in a carefully controlled furnace atmosphere filled with gases, such as hydrogen or nitrogen resulting in a clean, scale free metal surface.

Burst Pressure
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.

Chemical Analysis
A report of the chemical composition of the elements, and their percentage that form a stainless steel tube, all is stated on the test certification.

Chloride Stress Corrosion Cracking
Cracking due to the combination of tensile stress and corrosion in the presence of water and chlorides.

Coils
A reel of stainless steel tubes that has been rolled into a coil to facilitate transportation and storage.

Cold finished tubes
Hot rolled stainless steel tubes that are annealed and cold worked to produce a higher surface quality and higher strength.

Cold forming (Cold Working)
Any mechanical operation that creates permanent deformation, such as bending, rolling, drawing, etc. performed at room temperature that increases the hardness and strength of the stainless steel. This production method gives a better control on nominal dimensions, tolerances and surface finish without additional process, all Merinox Tubing are cold worked.

Concentricity
Used to describe tubing where the centre of its inside diameter is consistent with the outside diameter resulting in no variation of wall thickness.

Corrosion
The attack upon metals by chemical agents converting them to non-metallic products film created by the presence of chromium (and often other alloying elements like; nickel, molybdenum, titanium & niobium) that resists this process.

Corrosion Fatigue
Cracking due to repeating and fluctuating stresses in a corrosive environment.

Corrosion Potential
The potential of a corroding surface in an electrolyte relative to a reference electrode under open-circuit conditions.

Corrosion Resistance
A metal’s ability to resist corrosion in a particular environment.

De burring
Removing the subtle ridge from the edge of the tube that results from cutting operation.

Ductility
A measurement of the malleability of stainless steel in terms of the amount of deformation it will withstand before failure.

Duplex
Stainless steel comprised of austenitic and ferretic stainless steels that contain high amounts of chromium and nickel. This combination is stronger than both of the individual stainless steels. Duplex stainless steels are highly resistant to corrosion and cracking.

Eddy Current Testing
Non-destructive test procedure that examines for outside diameter cracks and burrs.

Electro polishing
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 micro inch) is attainable.

Elongation
A measurement of ductility expressed in terms of the stretch having occurred over a given length on a standard tensile specimen at time of fracture, usually based upon an original length of 2 inches.

Erosion
The continuous depletion of a material due to mechanical interaction with a liquid, a multicomponent fluid, or solid particles carried with the fluid.

Extrusion
A shaped piece of stainless steel produced tube by forcing the pre pipe, bar, or rod through a die of the appropriate shape.

Ferritic
Magnetic stainless steels that have a low carbon content and contain chromium as the main alloying element, usually between 13% and 17%. It is the second most widely used stainless steel. Ferritic stainless steels are generally used in automotive trim and exhaust systems, hot water tanks, and interior architectural trim.

Grain (Grain Boundary)
The individual crystal units comprising the aggregate structure where the crystalline orientation does not change. The grain boundary is where these individual crystal units meet.

Hardness Test
Hardness testing consists of pressing an indenter into a flat surface under a perfectly controlled load, then measuring the dimension of the resulting indentation. The three methods most commonly used for stainless steel are the Rockwell B, Rockwell C and Vickers tests. The higher the number, the harder the material.

Heat
Term referring to batch of refined stainless steel tube; a charged oxygen or electric furnace full of stainless steel. A heat of stainless steel can be used to cast several slabs, billets, or blooms.

Heat-Affected Zone (HAZ)
The part of a metal that is not melted during cutting, brazing, or welding, but whose microstructure and physical properties are altered by these processes.

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

Heat Treatment
Altering the properties of stainless steel by subjecting it to a series of temperature changes. To increase the hardness, strength, or ductility of stainless steel so that it is suitable for additional applications.

Hollow
Seamless raw material supplied for tube processing. This may be in the form of an extrusion or tube reduced product.

Hot Forming
Hot forming operations are used widely in the fabrication of stainless steel to take advantage of their lower resistance to shape change. High temperature reduces their yield strengths, and this results in a marked lowering of the force that is required to bring about plastic movement or flow from one shape to another (hot rolling, hot stretching, etc.).

Hydrogen Stress Cracking
Cracking of a metal resulting from the combination of hydrogen and tensile stress.

Hydrostatic Testing
A non-destructive 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.

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

Impact Test
Impact testing is used to measure the toughness of a material, corresponding to the energy necessary to cause fracture under shock loading. Low toughness is generally associated with brittle shear fracture and high toughness with ductile plastic tearing.

Intergranular Corrosion
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.

Line Pipe
A pipe extending over long distances that transports oil, natural gas, and other fluids.

Martensitic
A small category of magnetic stainless steels typically containing 12% chromium, a moderate level of carbon, and a very low lever of nickel.

Mechanical Properties (Physical Properties)
Properties determined by mechanical testing, such as yield strength, ductility, ultimate tensile strength, harness, bendability, impact strength, etc.

Molybdenum (Mo)
An alloying element that enhances corrosion resistance along with chromium in stainless steels.

Nickel (Ni)
An alloying element used in stainless steels to enhance ductility and corrosion resistance.

Nickel-Based Super Alloys
Alloy metal produced for high-performance, high-temperature applications such as nickel-iron-chrome alloys and nickel-chrome-iron alloys.

OD
Outside diameter of a tubular product.

Orbital Weld
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.

Ovality
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.

Oxidation
Rust or corrosion due to exposure to oxygen.

Passivation
When exposed in air, stainless steels passivate naturally (due to the presence of chromium). But the time required can vary. In order to ensure that the passive layer reforms rapidly after pickling, a passivation treatment is performed using a solution of nitric acid and water.

Pickling
A process that removes surface scale and oxidation products by immersion in a chemically active solution, such as sulphuric or hydrochloric acid.

Pitting
Localized corrosion (in the form of pits) of a metal surface that is confined to a small area.

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

Printing
Outside some capillary tubes, all our tubes are printed with information needed to verify such as; heat number, dimensions, material, smls ( seamless ), mill’s reference .This is printed along the length of all tubes dispatched.

Roughness Average (Ra)
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.

Seamless Tube
Tube produced from a solid billet that is heated and rotated under pressure. This rotating pressure creates a hole in the middle of the billet, which is then formed into a tube by a mandrel.

Sensitization
The phenomenon in austenitic stainless steels that causes a change to occur in the grain boundaries when heated in the general range of 850 to 1475 degree F. This change destroys the passivity in these locations.

Solution Heat Treatment
Heating a metal to a high temperature and maintaining it long enough for one or more constituents to enter the solid solution. The solution is then cooled rapidly to retain the constitutes within.

Stabilisation
An addition of titanium or niobium, making stainless steels less sensitive to intergranular corrosion.

Stainless Steel
Group of corrosion resistant steels containing at least 10.5% chromium and may contain other alloying elements. These steels resist corrosion and maintain its strength at high temperatures.

Stress Corrosion Cracking (SCC)
Slowly developing cracks that form in stainless steel due to mechanical stress and exposure to a corrosive environment.

Stress relieving
Heat treatment carried out in order to reduce internal stresses in steel.

Tensile Strength
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.

Tubing Dimensions
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

Yield Strength
The stress beyond which stainless steel undergoes important permanent flow – commonly specified as that stress producing a 0.2% or 1.0% offset from the linear portion of the stress-strain curve.