IIW IWI-S flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Heat input formula

Q (kJ/mm) = k × U × I × 60 / (1000 × v), where U is arc voltage in volts, I is current in amperes, v is travel speed in mm/min and k is process efficiency, typically 0.8 for SMAW and GMAW.

Spray transfer GMAW

A metal transfer mode in which fine droplets are projected axially across the arc above a transition current, using argon-rich shielding gas. It gives deep penetration, low spatter and is limited to flat and horizontal positions.

Duty cycle definition

The percentage of a ten-minute period during which a welding power source can operate at a given current without overheating. At 60 percent duty cycle, welding is permitted for six minutes, then cooling for four.

Low-hydrogen electrode storage

Basic-coated electrodes absorb moisture from air, which raises weld hydrogen and cracking risk. They must be baked at about 300 to 350 degrees Celsius and held in heated quivers at 100 to 150 degrees Celsius.

Carbon equivalent formula

CE = C + Mn/6 + (Cr+Mo+V)/5 + (Cu+Ni)/15, using weight percentages. Values above about 0.40 percent indicate high hardenability and the need for preheat, low-hydrogen consumables or post-weld heat treatment.

Hydrogen cracking conditions

Cracking in the weld or heat-affected zone requires three simultaneous factors: diffusible hydrogen, a susceptible hard microstructure and tensile stress. Preheat, low-hydrogen consumables and post-heating reduce the risk.

Sensitisation of austenitic stainless

Chromium carbide precipitation at grain boundaries during exposure to roughly 450 to 850 degrees Celsius depletes chromium locally. Corrosion resistance falls in the affected zone; low-carbon or stabilised grades prevent this.

Aluminium oxide film

Aluminium forms an oxide layer melting near 2050 degrees Celsius, far above the 660 degrees Celsius melting point of the metal. Alternating current or reverse polarity in GTAW breaks the oxide and allows fusion.

Delta ferrite in austenitic welds

Austenitic stainless steel weld metal often contains 5 to 10 percent delta ferrite, which resists solidification cracking. Prolonged exposure above about 550 degrees Celsius can transform ferrite to brittle sigma phase.

Fillet weld throat thickness

For a fillet weld with equal legs at 90 degrees, the design throat thickness a equals 0.707 times the leg length z. Strength calculations use the throat area, not the leg size.

ISO 2553 weld symbol sides

On the reference line, a symbol placed above the line denotes a weld on the arrow side of the joint. A symbol below the line denotes a weld on the other side.

Fatigue-critical joint design

Full-penetration butt welds with smooth, flush profiles give the highest fatigue strength. Fillet welds and transverse attachments create stress concentration and reduce fatigue life, especially under cyclic loading.

Residual stress relief

Post-weld heat treatment at roughly 550 to 650 degrees Celsius for carbon steels reduces residual stress by allowing creep relaxation. It also lowers hardness and improves dimensional stability of the fabrication.

Welding procedure qualification

A PQR records the test results of a welded test piece made to a proposed procedure. The WPS is then written from the qualified ranges of essential variables such as material group, thickness, filler and preheat.

Preheat measurement location

Preheat is checked on the thicker part, at least 100 mm from the joint edge, before welding starts. Interpass temperature is measured between passes and must stay below the specified maximum.

Tack weld requirements

Tack welds become part of the finished joint and must be made with qualified procedures and consumables. They must be sound, free of cracks and slag, and are inspected with the final weld.

Back-step welding technique

Welding is performed in short segments, with each new pass started ahead of the previous one and directed back toward it. This balances shrinkage and reduces distortion and residual stress in thin sections.

Visual testing illumination

Visual inspection requires adequate lighting, commonly at least 500 lux at the weld surface, plus good access and eyesight. It detects surface discontinuities such as undercut, overlap, spatter and dimensional errors.

Magnetic particle testing principle

A magnetic field is induced in ferromagnetic material; surface or near-surface discontinuities distort the flux and attract particles. Alternating current favours surface defects, direct current gives some subsurface sensitivity.

Radiographic testing limitations

Radiography detects volumetric defects such as porosity and slag. Planar defects like cracks or lack of fusion oriented parallel to the beam may not be detected, so ultrasonic testing is often used in addition.

Bend test purpose

A destructive test in which a welded specimen is bent through a specified angle to assess ductility and root fusion. Cracks or open defects on the tension face indicate unacceptable weld quality.

NDT personnel levels

ISO 9712 defines three levels. Level 1 performs tests under supervision, level 2 sets up and interprets results per procedure, and level 3 develops procedures and approves techniques and personnel.

Quality assurance versus control

Quality assurance is preventive and process-oriented, ensuring the system can produce conforming work. Quality control is product-oriented, inspecting and testing finished work to detect nonconformities against acceptance criteria.

ISO 3834 scope

This standard specifies quality requirements for fusion welding of metallic materials. Parts 2, 3 and 4 cover comprehensive, standard and elementary requirements, chosen according to product criticality and contract.

Essential variables in WPS

Parameters whose change beyond qualified limits requires requalification: base material group, thickness range, filler classification, welding process, position, preheat and post-weld heat treatment. They are defined in the applicable standard.

Nonconformance report content

A record of a deviation from specification, including location, description, extent, disposition such as rework, repair, concession or scrap, and the corrective action taken. Traceability to the weld number is maintained.

Material certificate 3.1

An inspection certificate issued by the manufacturer's authorised inspection representative, stating that the delivered product complies with the order and giving specific test results. It provides full material traceability.

Welding fume control

Local exhaust ventilation must capture fume at the arc. Manganese and hexavalent chromium from stainless steel are significant hazards, so extraction, respiratory protection and air monitoring are used in confined spaces.

Arc eye prevention

Ultraviolet radiation from the arc causes painful photokeratitis. Welders need helmets with correct filter shade, typically 10 to 13 for high-current arc welding, and nearby workers need protective screens.

Acetylene pressure limit

Acetylene is unstable and must never be used at a gauge pressure above about 1.5 bar. Flashback arrestors are fitted on both the torch and regulator sides to prevent flame travel into the cylinder.

Discontinuity versus defect

A discontinuity is any interruption in the weld, such as porosity or slag. It is classified as a defect only when its size or nature exceeds the acceptance criteria of the applicable standard, such as ISO 5817.

Inspection report essentials

A report identifies the project, component and weld number, references drawings, WPS and standard, states the method and date, records findings and acceptance status, and carries the inspector's name and signature.