Definitions, terms, and acronyms related to: construction, HVAC systems, mechanical engineering, materials engineering, welding, inspection, nondestructive examination, rigging, industrial rope access, pressure vessels, pressure piping, storage tanks, and the power generation and petrochemical industries.


Abrasion – The removal of surface material from any solid through the frictional action of another solid, a liquid, or a gas or combination thereof.

Absolute Pressure – The pressure above the absolute zero value of pressure that theoretically obtains in empty space or at the absolute zero of temperature, as distinguished from gauge pressure.

Acceleration Stress – Additional stress imposed by an increase in the load velocity.

Aggregate Strength – The wire rope strength derived by totaling the individual breaking strengths of the elements of the strand or rope. This strength does not recognize the reduction in strength resulting from the angularity of the elements in the rope or from other factors that may affect efficiency.

Aid Climbing – Method of progression in suspension, either by moving from one fixed anchor to another or by the use of moveable anchors or anchor points.

Alligatoring – Extensive surface cracking in a pattern that resembles the hide of an alligator.

Alloy – Any of a large number of substances having metallic properties and consisting of two or more elements; with few exceptions, the components are usually metallic elements.

Alternating Current – (AC) An electric current that reverses direction at regular intervals, having a magnitude that varies continuously in sinusoidal manner.

Alternate Lay – Lay of wire rope in which the strands are alternately regular lay and lang lay.

Ampere – (Amp) The basic unit of electrical current in the International System of Units (SI), equivalent to one coulomb per second.

Anchor – Fixture for the secure attachment of anchor lines or persons. Also known as a belay.

Anchor Point – Attachment point at an anchor for anchor lines or persons.

Angle Joint – A joint between two members located in intersecting planes between zero (a butt joint) and 90 deg. (a corner joint).

Angle of Loading – The inclination of a leg or branch of a sling measured from the horizontal or vertical plane, provided that an angle of five degrees or less from the vertical may be considered a vertical angle of loading.

Angle Valve – A valve, usually of the globe type, in which the inlet and outlet are at right angles.

Annealing – Annealing generally refers to the heating and controlled cooling of solid material for the purpose of removing stresses, making it softer, refining its grain structure or changing its ductility, toughness or other properties.

API – American Petroleum Institute.

Arc Welding – A group of welding processes wherein coalescence is produced by heating with an electric arc, with or without the application of pressure and with or without the use of filler metal.

Areaway – An open subsurface space around a basement window or doorway; provides light, ventilation, and access.

Ascender – Rope adjustment device which, when attached to an anchor line of appropriate type and diameter, locks under load in one direction and slides freely in the opposite direction.

ASHRAE – American Society of Heating, Refrigerating and Air-Conditioning Engineers.

ASME – American Society of Mechanical Engineers.

ASNT – American Society for Nondestructive Testing.

ASTM – American Society for Testing Materials.

Automatic Welding – Welding with equipment which performs the entire welding operation without constant observation and adjustment of the controls by an operator. The equipment may or may not perform the loading and unloading of the work.

AWG – American Wire Gage.

AWS – American Welding Society.


Backfill – The gravel or earth replaced in the space around a building wall after the foundation is in place.

Back-Up Device – Rope adjustment device for a safety line of appropriate type and diameter, which accompanies the user during changes of position or allows adjustment of the length of the safety line, and which locks automatically to the safety line, or only allows gradual movement along it, when a sudden load is applied.

Backing – Material backing up the joint during welding to facilitate obtaining a sound weld at the root. Backing strip is a backing in a form of a strip.

Bail – (a) The U-shaped member of a bucket or load usually used as a lifting point; or (b) a U-shaped portion of a socket, or other fitting used on wire rope.

Base – The mounting flanges or feet used to attach a hoist to its supporting structure or foundation.

Basket Hitch – A sling configuration whereby the sling is passed under the load and has both ends, end attachments, eyes, or handles on the hook or a single master link.

Beam – A horizontal structural component, usually wood or steel, that is typically supported by a foundation wall or column. A beam is generally used to support floor joists.

Becket – A wedge socket type wire rope end termination.

Block – A term applied to a wire rope sheave (pulley) enclosed inside plates and fitted with some attachment such as a hook or shackle.

Bottom Plate – The bottom horizontal member of a frame wall.

Brake – A device used for retarding or stopping motion by friction or power means.

Breaking Strength – The measured tensile load required to cause failure of cable, chain, wire rope, or any other load-bearing element.

Breaking Strength/Ultimate Strength – The average force (Minimum Breaking Load) at which the product, in the condition it would leave the factory, has been found by representative testing to break, when a constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull testing machine. Do NOT use breaking strength as a criterion for service or design purposes. Refer to the Working Load Limit instead.

Bridle Sling – Sling composed of multiple wire rope legs with a fitting that attaches to the lifting block.

Brittle Fracture – The tensile failure with negligible plastic deformation of an ordinary ductile metal.

Brittleness – Materials are said to be brittle when they show practically no permanent distortion before failure.

BTU – (British Thermal Unit) The amount of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.

Bull Ring – The main, large ring of a sling to which legs are attached; also called master link.

Bulldog Clip – A wire rope cable clamp or clip.

Bushing – A pipe fitting for connecting a pipe with a female fitting of larger size. It is a hollow plug with internal and external threads.

Butt Weld – A weld joining two members lying approximately in the same plane.


Cable – A term loosely applied to wire ropes, wire strand, and electrical conductors. Wire Rope is the preferred term for hoisting and rigging application.

Cable-Laid Wire Rope – A wire rope consisting of several independent wire ropes wrapped around a fiber or wire rope core.

Camber – The slight curvature given to beams and girders to compensate for deflections caused by loading.

Cantilever – A structural member that projects beyond its supporting wall or column.

Certificate of Conformity – Documentation provided by a supplier of equipment at the time of purchase or rental, stating performance specifications of the equipment or indicating conformity to known standards or compliance with relevant legislation.

Check Valve – A valve designed to allow a fluid to pass through in one direction only.

Cheek Plate – The stationary plate that supports the pin (axle) of a sheave or load.

Choker Sling – Wire rope with eyes spliced on each end, which is used to lift load.

Choker Hitch – A sling configuration with one end of the sling passing under the load and through an end attachment, handle, or eye on the other end of the sling.

Clad Vessel – A vessel made from plate having corrosion resistant material integrally bonded to a base of less resistant material.

Clevis – A U-shaped fitting with holes in each end through which a pin or bolt is run.

Clip – Fitting for clamping two parts of wire rope.

Closed Socket – Wire rope end fitting consisting of integral basket and ball.

Come-Along – A lever-operated chain or wire rope device designed for pulling, not lifting; also called a puller. Unlike hoists, the tension is held by a releasable ratchet.

Competent Person – Designated person suitably trained or qualified by knowledge and practical experience to enable the required task or tasks to be carried out properly.

Complete Fusion – Fusion which has occurred over the entire base-metal surfaces exposed for welding.

Complete Penetration – Penetration which extended completely through the welded joint.

Compressor – The component of an air conditioning or heat pump system that forces refrigerant to travel through the system and also changes a low pressure vapor to a high pressure vapor.

Condensate – The water (condensed humidity) that drips from a cooling coil on an air conditioning system and flows to a drain.

Condenser – The component of an air conditioning or refrigeration system that cools hot refrigerant vapor to the point where it changes state and becomes a liquid.

Connector – Openable device used to connect components, which enables the user to link himself directly or indirectly to the anchor.

Control Joint – A groove that is formed, sawed, or tooled in a concrete or masonry structure to regulate the location and amount of cracking.

Core – Member of wire rope about which the strands are laid. It may be fiber, a wire strand, or an independent wire rope.

Corner Joint – A welded joint at the junction of two parts located approximately normal (at right angles) to each other.

Cornice – A horizontal projection at the top of a wall or under the overhanging portion of the roof.

Corrosion – Chemical erosion by motionless or moving agents. Gradual destruction of a metal or alloy due to chemical processes such as oxidation or the action of a chemical agent.

Corrosion Fatigue – Damage to or failure of a metal due to corrosion combined with fluctuating fatigue stresses.

Corrugated – A term used to describe the grooves of a sheave or drum when worn so as to show the impression of wire rope.

Coupling – A threaded sleeve used to connect two pipes. They have internal threads at both ends to fit external threads on pipe.

Cow’s Tail – Short strop, lanyard, or sling connected to the main attachment point of a harness.

Craneway – The area in length and width served by a crane.

Creep – Continuous increase in deformation under constant or decreasing stress. The term is usually used with reference to the behavior of metals under tension at elevated temperatures. The similar yielding of a material under compressive stress is usually called plastic flow.


D/d Ratio – A term regarding wire rope. D = Diameter of curvature around which the rope is bent.   d = diameter of rope. The D/d ratio is a key factor in load-carrying ability and life span of a wire rope.

Deadman – An object or structure, either existing or built for the purpose, used as anchorage for a guy rope.

Deflection – (a) The sag across a span of a load member caused by the imposed live and/or dead loads, which is usually measured at mid-span as the distance along a straight horizontal line drawn between the supports; (b) any deviation from a straight horizontal line.

Deformation (Strain) – Change in the form or in the dimension of a body produced by stress.Elastic deformation is such deformation as disappears on removal of stress; permanent deformation is such deformation as remains on removal of stress.

Derrick – An apparatus for lifting or lowering loads, consisting of a mast or equivalent member held at the head by guys or braces, with or without a boom, for use with hoists and ropes.

Descender – Manually operated, friction inducing, rope adjustment device, which when attached to an anchor line of appropriate type and diameter, allows the user to achieve a controlled descent and stop with hands off anywhere on the anchor line.

Design Factor – (aka Safety Factor) An industry term usually computed by dividing the catalog Breaking Strength by the catalog Working Load Limit and generally expressed as a ratio.

Design Pressure – The pressure used in determining the minimum permissible thickness or physical characteristics of the different parts of the vessel.

Design Temperature – The mean metal temperature (through the thickness) expected under operating conditions for the part considered.

Dog Leg – Permanent short bend or kink in wire rope caused by improper use.

Double-Welded Butt Joint – A butt joint welded from both sides.

Double-Welded Lap Joint – A lap joint in which the overlapped edges of the members to be joined are welded along the edges of both members.

Downdraft – A downward current of air in a chimney, often carrying smoke with it.

Dry Well – A covered pit, either with open-jointed lining or filled with coarse aggregate, through which drainage from downspouts or foundation footing drains may seep into surrounding soil.

Ductility – The ability of a metal to stretch and become permanently deformed without breaking or cracking. Ductility is measured by the percentage reduction in area and percentage elongation of the test bar.

Dynamic Loading – Loads introduced into the machine or its components by forces in motion.

Dynamic Rope – Rope specifically designed to absorb energy in a fall by stretching, thereby minimizing the impact force.


Eccentricity – A load or component of a load normal to a given cross section of a member is eccentric with respect to that section if it does not act through the centroid.

Efficiency of a Welded Joint – The efficiency of a welded joint is expressed as a numerical quantity and is used in the design of a joint as a multiplier of the appropriate allowable stress value.

Elastic – Capable of sustaining stress without permanent deformation; the term is also used to denote conformity to the law of stress-strain proportionality. An elastic stress or elastic strain is a stress or strain within the elastic limit.

Elastic Limit – Limit of stress above which a permanent deformation takes place within the material. This limit is approximately 55 to 65% of breaking strength of steel wire ropes.

Endless Rope – Rope whose two ends are spliced together.

Endurance Limit (Fatigue Limit) – The maximum stress that a material can endure for an infinite number of stress cycles without breaking.

Endurance Strength (Fatigue Strength) – The maximum stress that a material can endure for a given number of stress cycles without breaking.

Energy Absorber – Component or components in a fall arrest system, designed to minimize the impact force generated in a fall.

Equalizer – Device used to compensate for unequal length or stretch of a hoist rope and connects two or more systems to a single running block.

Erosion-Corrosion – Attack on a metal surface resulting from the combined effects of erosion and corrosion.

Evaporator – The portion of an air conditioning system installed in the duct work above a furnace. Its function is to cause liquid refrigerant to expand suddenly into a gas, thus causing an evaporation and cooling effect as a result of the change of state.

Expansion Joint – A joint whose primary purpose is not to join pipe but to absorb that longitudinal expansion in the pipe line due to heat.

Eye or Eye Splice – A loop with or without a thimble formed in the end of a wire rope.

Exclusion Zone – Zone designated to exclude the public from a hazardous area and from the rope access equipment, or to exclude the operatives from a hazardous area, unless suitably protected.


Factor of Safety – See Design Factor.

Fail-Safe – A provision designed to automatically stop or safely control any motion in which a malfunction occurs.

Fatigue – The phenomenon leading to fracture under repeated or fluctuating stresses having a maximum value less than the tensile strength of the material.

Fascia – A horizontal board nailed vertically to the ends of roof rafters; sometimes supports a gutter.

Fiber Stress – A term used for convenience to denote the longitudinal tensile or compressive stress in a beam or other member subject to bending.

Filler Metal – Material to be added in making a weld.

Fillet Weld – A weld of approximately triangular cross section joining two surfaces approximately at right angles to each other. The effective stress-carrying area of a fillet weld is assumed to be the product of the throat dimension and the length of the weld. Fillet welds are specified by their legdimension.

Flashing – Sheet metal or other thin, impervious material used around roof and wall junctions to protect joints from water penetration.

Flemish Eye – A type or method of making a wire rope eye splice. Same as a “Molly Hogan”.

Flue – A passageway in a chimney for conveying smoke, gases, or fumes to the outside air.

Footblock – A steel weldment or assembly serving as the base mounting for a guy derrick, gin pole, or boom derrick.

Footing – An enlargement at the bottom of a wall or column for the purpose of spreading the weight over a larger area. It is usually made of concrete.

Frost Line – The depth of frost penetration in soil; varies in different parts of the country.

Full Fillet Weld – A fillet weld whose size is equal to the thickness of the thinner member joined.


Gage Pressure – The amount by which the total absolute pressure exceeds the ambient atmospheric pressure.

Galvanized Rope – Wire rope made of galvanized wire.

Galvanizing – Applying a coating of zinc to ferrous articles. Application may be by hot dip process or electrolysis.

Gas Welding – A group of welding processes wherein coalescence is produced by heating with a gas flame with or without application of pressure and with or without the use of filler metal.

Grades, Rope – Classification of wire rope by its breaking strength. Listed in order of increasing breaking strengths: iron, traction, mild plow steel, plow steel, improved plow steel, and extra-improved plow steel.

Grooved Drum – Drum with a grooved surface that accommodates and guides the rope.


Handle – A terminal fitting to which metal mesh fabric is attached.

Handle Eye – An opening in a handle of a metal mesh sling shaped to accept a hook, shackle, or other lifting device.

Head – The end (enclosure) of a cylindrical shell. The most commonly used types of heads are hemispherical, ellipsoidal, flanged and dished (torispherical), conical, and flat.

Heat Treatment – Heat treating operation performed either to produce changes in mechanical properties of the material or to restore its maximum corrosion resistance. There are three principal types of heat treatment; annealing, normalizing, and post-weld heat treatment.

High Alloy Steel – Steel containing large percentages of elements other than carbon.

Hitch – A sling configuration whereby the sling is fastened to an object or load, either directly to it or around it.

HMI – Hoist Manufacturers Institute

Hook Latch – A mechanical device used to bridge the throat opening of a hook.

Hydrogen Brittleness – Low ductility of a metal due to its absorption of hydrogen gas, which may occur during an electrolytic process or during cleaning. Also known as acid brittleness.


Idler – Sheave or roller used to guide or support a rope. Also used as a slang expression for an equaling sheave.

Impact Stress – Force per unit area imposed to material by a suddenly applied force.

Impact Test – Determination of the degree of resistance of a material to breaking by impact, under bending, tensile and torsion loads; the energy absorbed is measured by breaking the material by a single blow.

Independent Wire Rope Core (IWRC) – Wire rope used as the core of a larger rope.

Intermittent Weld – A weld whose continuity is broken by unwelded spaces.

Internally Lubricated – Wire rope or strand in which all wires are coated with lubricant.

ISO – International Standards Organization.

Isotropic – Having the same properties in all directions. Pertaining to strength of materials, isotropic usually means having the same strength and elastic properties (modulus of elasticity, modulus of rigidity, Poisson’s ratio) in all directions.


Jib – An extension attached to the boom point to provide added boom length for lifting specified loads.

Jog (inch) – To move the hook, trolley, or bridge in a series of short, discontinuous increments by momentary operation of a controller.

Joint Efficiency – A numerical value expressed as the ratio of the strength of a riveted, welded, or brazed joint to the strength of the parent metal.

Joint Penetration – The minimum depth a groove weld extends from its face into a joint, exclusive of reinforcement.

Killed Steel – Thoroughly deoxidized steel, (for example, by addition of aluminum or silicon), in which the reaction between carbon and oxygen during solidification is suppressed. This type of steel has more uniform chemical composition and properties as compared to other types.

Kink – Permanent distortion of wires and strands resulting from sharp bends.


Lang Lay Rope – Wire rope in which the wires in the strands and the strands in the rope are laid in same direction. Synonymous with Albert’s Lay.

Lap Joint – A welded joint in which two overlapping metal parts are joined by means of a fillet, plug, or slot welds.

Lay – The manner in which the wires in a strand or the strands in a rope are helically laid.

Lifting Eye – A point of attachment on the item to be lifted, having a looped head designed to accommodate a hook or shackle.

Lined Vessel – A vessel having a corrosion resistant lining attached intermittently to the vessel wall.

Line – Rope used for supporting and controlling a suspended load.

Link – A single ring of a chain.

Load – The total superimposed weight or force to be overcome by the hoisting and rigging equipment.

Low-Alloy Steel – A hardenable carbon steel generally containing not more than about 1% carbon and one or more of the following alloyed components: <2% manganese, <4% nickel, <2% chromium, 0.6% molybdenum, and <0.2% vanadium.


Malleable Iron – Cast iron heat-treated to reduce its brittleness. The process enables the material to stretch to some extent and to stand greater shock.

Master Link – Forged or welded steel link used to support all members (legs) of an alloy-steel chain or wire rope sling. Also called bull-ring.

Master Coupling Link – An alloy steel welded coupling link used as an intermediate link to join alloy steel chain to master links.

Material Test Report – A document on which the material manufacturer records the results of test examinations, repairs, or treatments required by the basic material specification to be reported.

Maximum Allowable Working Pressure (MAWP) – The maximum gage pressure permissible at the top of a completed vessel in its operating position for a designated temperature. This pressure is based on the weakest element of the vessel using nominal thickness exclusive of allowances for corrosion and thickness required for loadings other than pressure.

Mechanical Coupling Link – A nonwelded, mechanically closed steel link used to attach master links, hooks, etc., to alloy steel chain.

Messenger Sling – A short, standard eye-eye wire rope sling, often used to connect between a crane hook and another wire rope sling or bridle; also known as a pig tail.

Metal Arc Welding – An arc welding process in which the electrode supplies the filler metal to the weld.

Modulus of Elasticity (Young’s Modulus) – The rate of change of unit tensile or compressive stress with respect to unit tensile or compressive strain for the condition of uniaxial stress within proportional limit.


Neutral Axis – The line of zero fiber stress in any given section of a member subject to bending; it is the line formed by the intersection of the neutral surface and the section.

Nominal Strength – Nominal wire rope strengths as calculated by a standardized industry-accepted procedure. Minimum acceptance strength is 22% lower than nominal strength.

Nondestructive Examination (NDE) – Determination of the physical condition of an object without affecting that object’s ability to fulfill its intended function. NDE methods typically use an appropriate form of energy to determine material properties or to indicate the presence of material discontinuities. Also called nondestructive evaluation, nondestructive inspection, or nondestructive testing.

Nondestrcutive Testing (NDT) – See Nondestructive Examination (NDE).

Non-Pressure Welding – A group of welding processes in which the weld is made without pressure.

Normal – Being at right angles, as a line; perpendicular.

Normalizing – Heating metal to about 100 deg. F above the critical temperature and cooling to room temperature in still air.

Notch Strength – The ratio of maximum tensional load required to fracture a notched specimen to the original minimum cross-sectional area.

Notch Test – A tensile or creep test of a metal to determine the effect of a surface notch.



Operating Pressure – The pressure at the top of a pressure vessel at which it normally operates. It shall not exceed the maximum allowable working pressure (MAWP).

Overload – Any load in excess of the safe working load or rated capacity of the equipment or tackle.

Oxidation – or scaling of metals occurs at high temperatures and access of air. Scaling of carbon steels from air or steam is negligible up to 1,000 deg. F. Chromium increases scaling resistance of carbon steels. Decreasing oxidation resistance makes austenitic stainless steels unsuitable for operating temperatures above 1,500 deg. F.


P-Number – The number of welding procedure-group. The classification of materials is based on the hardenability characteristic. The purpose of grouping is to reduce the number of weld procedures (Refer to ASME Section IX).

Pass – The weld metal deposited by one progression along the axis of a weld.

Paying Out – Adding slack to a line or relieving load on a line by letting (spooling) out rope.

Peening – Permanent distortion of outside wire in a rope caused by pounding.

Pig Tail – A short, standard eye-eye wire rope sling, often used to connect between a crane hook and another wire rope sling or bridle; also known as a messenger sling.

Plasticity – The property of sustaining appreciable permanent deformation without rupture. The term is also used to denote the property of yielding or flowing under steady load.

Pneumatic Test – A completed vessel may be tested by air pressure in lieu of hydrostatic test when the vessel cannot safely be filled with water or the traces of testing liquid cannot be tolerated. The pneumatic test shall be 1.25 times the maximum allowable working pressure (MAWP) to be stamped on the vessel.

Poisson’s Ratio – The ratio of lateral unit strain to longitudinal unit strain, under the condition of uniform and uniaxial longitudinal stress within the proportional limit.

Porosity – Gas pockets or voids in metal.

Postweld Heat Treatment – Heating metal to a sufficient temperature to relieve the residual stresses which are the result of mechanical treatment and welding.

Preheating – Heat applied to base metal prior to welding operations.

Pressure Relief Valve – A valve which relieves pressure beyond a specified limit and recloses upon return to normal operating conditions.

Pressure Vessel – A metal container generally cylindrical or spheroid, capable of withstanding various loadings.

Pressure Welding – A group of welding processes wherein the weld is completed by use of pressure.

Prestressing – Stressing a wire rope or strand before use under such a tension and for such a time that the construction stretch is largely removed.

Proof Test Load (Proof Load) – The term “Proof Test” designates a quality control test applied to the product for the sole purpose of detecting defects in material or manufacture. The Proof Test Load (usually twice the Working Load Limit) is the load which the product withstood without deformation when new and under laboratory test conditions. A constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull testing machine. The Proof test load does not mean the Working Load Limit should ever be exceeded.

Quench Annealing – Annealing an austenitic ferrous alloy by heating followed by quenching from solution temperatures. Liquids used for quenching are oil, fused salt or water, into which a material is plunged.


Rated Load – The maximum load designated by the manufacturer for which a crane, hoist, rigging, or other lifting device is designed and built.

Refractory – A material of very high melting point with properties that make it suitable for such uses as high-temperature lining.

Regular-Lay Rope – Wire rope in which the wires in the strands and the strands in the rope are laid in opposite directions.

Rerate – To change the rated load capacity. The rated capacity may be increased or decreased.

Residual Stress – Stress remaining in a structure or member as a result of thermal or mechanical treatment, or both.

Resistance Welding – A pressure welding process wherein the heat is produced by the resistance to the flow of an electric current.

Reverse Lay – See alternate lay.

Rigging – The act of attaching hoisting equipment to the load.

Rocker Beam – Beam used for hoisting flimsy trusses or long flimsy loads. Also used to equalize the weight and to keep a load, such as tank plate, from buckling.

Root of Weld – The bottom of the weld.


Safe Working Load (SWL) – The maximum load a piece of equipment (or tackle) can handle without exceeding the rated capacity (the rated capacity of the lowest capacity item used in the lift).

Scale – An iron oxide formed on the surface of hot steel, sometimes in the form of large sheets which fall off when the sheet is rolled.

Scarf – Edge preparation; preparing the contour on the edge of a member for welding.

Seizing Strand – Small strand, usually of seven wires, made of soft-annealed-iron wire.

Seizing Wire – A soft-annealed-iron wire.

Shackle – A type of clevis normally used for lifting.

Shear Stress – The component of stress tangent to the plane of reference.

Shock Load – A load resulting from rapid change of movement, such as impacting, jerking, or swinging of a static load. Sudden release of tension is another form of shock loading. Shock loads are generally significantly greater than static loads. Any shock loading must be considered when selecting the item for use in a system. Avoid shock loads as they may exceed the Working Load Limit.

Side Loading – A loading applied at any angle to the vertical plane of the boom.

Slag – A result of the action of a flux on nonmetallic constituents of a processed ore, or on the oxidized metallic constituents that are undesirable.

Slenderness Ratio – The ratio of the length of a uniform column to the least radius of gyration of the cross section.

Slings – Wire ropes, chains, or synthetic fabric made into forms, with or without fittings, for handling loads.

Snatch Block – A single or double-sheave block arranged so one or both cheek plates can be opened, permitting the block to be reeved without having to use a free rope end; also called a gate block. The brand name SKOCUM is also used generically; thus snatch blocks are also called skocum blocks.

Softeners – Anything used to protect the load or the rigging from damage while making a lift. Also, prevents the load from slipping.

Spooling (rope) – Winding of rope on a cylindrical drum in evenly spaced, uniformed layers.

Spreader Bar – A frame, forming part of the boom suspension, supporting sheaves for the live suspension ropes and attached to the fixed suspension ropes (pendants); also called bridle, spreader, live spreader, or flating harness.

Spreader Beam – A fixture made of rigid parts, such as pipe, wide-flange, I-beam, channel, plate, etc., to assist in rigging a load; also called lifting beam.

Static Head – The pressure of liquids that is not moving, against a vessel wall, is due solely to the “Static Head”, or height of the liquid.

STI/SPFA – Steel Tank Institute/Steel Plate Fabricators Association.

Strain – Any forced change in the dimensions of a body. A stretch is a tensile strain; a shortening is a compressive strain; and angular distortion is a shear strain.

Stress – Internal force exerted by either of two adjacent parts of a body upon the other across an imagined plane of separation.


Tack Weld – A weld made to hold parts of a weldment in proper alignment until the final welds are made.

Tee Joint – A welded joint at the junction of two parts located approximately at right angles to each other in the form of a “T”.

Tensile Strength – The maximum stress a material subjected to a stretching load can withstand without tearing.

Thermal Fatigue – The development of cyclic thermal gradients producing high cyclic thermal stresses and subsequent local cracking of material.


U.M. Plate – Universal Mill Plate or plate rolled to width by vertical rolls as well as to thickness by horizontal rolls.

Undercut – A groove melted into the base metal adjacent to the toe of a weld and left unfilled by weld metal.

Unit Strain – Unit tensile strain is the elongation per unit length; unit compressive strain is the shortening per unit length; unit shear strain is the change in angle (radians) between two lines originally at right angles to each other.

Unit Stress – The amount of stress per unit of area.

Vessel – A container or structural envelope in which materials are processed, treated, or stored; for example, pressure vessels, reactor vessels, agitator vessels, and storage vessels (tanks).


Weaving – A technique of depositing weld metal in which the electrode is oscillated from side to side.

Weld – A localized coalescence of metal produced by fusion with or without use of filler metal, and with or without application of pressure.

Weld Metal – The metal resulting from the fusion of the base metal and the filler metal.

Welding – The metal joining process used in making welds.

Welding Procedure – The materials, detailed methods, and practices involved in the procedure of a welded joint.

Welding Rod – Filler metal, in wire or rod form, used in the gas welding process, and in those arc welding processes wherein the electrode does not furnish the deposited metal.

Working Load Limit (WLL) – The maximum load which an item of lifting equipment is designed to raise, lower, or suspend. This load represents a force that is much less than that required to make the lifting equipment fail or yield, also known as the Minimum Breaking Load (MBL). See Breaking Strength/Ultimate Strength. WLL is calculated by dividing MBL by a Factor of Safety (Design Factor). The Factor of Safety is usually 5.

Wrought Iron – Iron refined to a plastic state in a pudding furnace. It is characterized by the presence of about 3% of slag irregularly mixed with pure iron and about 0.5% carbon.


X-Ray – Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release energy. Radiation is nonisotopic in origin and is most often generated by bombarding a metallic target with high speed electrons.

Yankee – the term “Yankee” and its contracted form “Yank” have several interrelated meanings, all referring to people from the USA. To foreigners, a Yankee is an American. To Americans, a Yankee is a Northerner. To Northerners, a Yankee is an Easterner. To Easterners, a Yankee is a New Englander. To New Englanders, a Yankee is a Vermonter. And in Vermont, a Yankee is somebody who eats pie for breakfast.

Yield Point – The lowest stress at which strain increases without increase in stress. For some purposes it is important to distinguish between the upper yield point, which is the stress at which stress-strain diagram first becomes horizontal, and the lower yield point, which is the somewhat lower and almost constant stress under which the metal continues to deform. Only a few materials exhibit a true yield point; for some materials the term is sometimes used synonymous with yield strength.

Yoke – In magnetic particle testing (MT), portable U-shaped electromagnet or permanent magnet that induces longitudinal magnetization in the region of the test object between its magnetic poles.

Young’s Modulus – See Modulus of Elasticity.

Zone – Inline scanners for infrared testing, a scanned area created by the transverse linear motion of the product or process under a measurement sector of the scanner.