GaugePass

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Processes and examination methods

Every process leaves its own signature on a weld, and every examination method has a blind spot. Knowing which is which is the difference between inspecting a weld and looking at one.

Welding processes

7 pages
Covering burns to shieldSlag freezes over the bead
SMAWShielded metal arc weldingManual stick welding, where a consumable covered electrode carries the current, melts to supply filler metal, and burns its own covering to shield and refine the weld pool.
Solid wire fed continuouslyGas shield from the nozzle
GMAWGas metal arc weldingA continuously fed solid wire electrode burns in an arc protected by shielding gas from the gun nozzle, giving high deposition and no slag to remove between passes.
Tubular wire, flux in the coreSlag covers the bead
FCAWFlux cored arc weldingA continuously fed tubular wire filled with flux, run either with additional shielding gas or entirely self-shielded, combining wire-feed productivity with the slag and forgiveness of a covered electrode.
Tungsten does not meltFiller added by hand
GTAWGas tungsten arc weldingAn arc burns between a non-consumable tungsten electrode and the work under inert gas shielding, with filler added separately by hand, giving the cleanest and most precisely controlled arc weld.
Granular flux buries the arcNo visible light, no spatter
SAWSubmerged arc weldingA continuously fed bare wire burns under a blanket of granular flux, so the arc is completely buried and enormous currents can be used without arc flash, spatter, or fume escaping.
Resistance of the slagdoes the melting
ESWElectroslag weldingA vertical joint is filled in a single continuous pass as wire melts in a bath of electrically resistive molten slag held between water-cooled shoes, with no arc burning after start-up.
Chemical flame, not an arcInner cone does the heating
OFWOxyfuel gas weldingA flame produced by burning fuel gas in oxygen melts the joint while filler rod is added by hand, the oldest fusion welding method still valued for its total control of heat.

Nondestructive examination

5 pages
Light, angle and accessEverything else follows VT
VTVisual testingDirect examination of the weld and surrounding material with the eye, aided by light, gauges, and optical instruments, and the only method applied before, during, and after welding.
Capillary action fills the crackDeveloper bleeds it back out
PTLiquid penetrant testingA coloured or fluorescent liquid is drawn into surface-breaking flaws by capillary action, then bled back out onto a developer so tight cracks become visible indications.
Field leaks at the flawParticles gather on the leak
MTMagnetic particle testingA magnetic field is induced in ferromagnetic material, and fine iron particles gather at the flux leakage caused by a crack, marking surface and slightly subsurface flaws.
Sound in, echo backOrientation decides what returns
UTUltrasonic testingHigh-frequency sound is injected into the material and the echoes returning from internal reflectors are timed and measured, giving both the depth and the size of buried flaws.
Density difference makes the imageVolumetric, and it keeps a record
RTRadiographic testingPenetrating radiation passes through the weld onto film or a digital detector, and differences in how much is absorbed produce a permanent image of the joint's internal condition.