API 577 cheat sheet

Quality control performs inspections and tests; quality assurance is the planned system that verifies those controls are defined, followed, and documented.

Heat input (kJ/in) = (arc voltage × amperage × 60) ÷ (travel speed in in/min × 1000); record it against the WPS range.

Hold point: work cannot proceed until inspection is completed and accepted; witness point: the inspector is notified and may observe, but work continues if absent.

Pre-weld inspection verifies base metal identity, joint fit-up and cleanliness, preheat, WPS availability, consumable condition, and welder qualification.

Carbon equivalent (AWS) = C + (Mn+Si)/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15; higher CE increases hardenability and the preheat required.

Typical quality package: WPS, PQR, welder performance qualifications, NDE reports, heat-treatment charts, material certificates, and as-built records.

Positive material identification by XRF or OES is used when alloy identity cannot be confirmed from markings or when the specification requires it.

On a nonconformance, tag and segregate the item, document the deviation, and obtain engineering disposition before any repair welding.

SMAW uses a flux-coated consumable electrode; the flux provides shielding gas and a slag layer that must be removed between passes.

GTAW uses a nonconsumable tungsten electrode with separately supplied filler and produces high-purity welds, commonly used for root passes.

SAW uses a continuous wire under a granular flux blanket; high deposition rates are limited to flat and horizontal positions.

Essential variables for procedure qualification include base metal group, filler classification, position, preheat and interpass temperature, PWHT, and current type/polarity.

PQR testing typically includes tensile and guided-bend specimens, plus impact and hardness tests where the specification requires them.

Welder performance qualification is specific to process, position, and thickness; a 6G groove test qualifies all positions within stated limits.

GMAW transfer modes are short-circuiting, globular, and spray; spray transfer requires an argon-rich shielding gas and higher current density.

Self-shielded FCAW needs no external shielding gas, while gas-shielded FCAW generally gives better toughness and lower fume generation.

Hydrogen-induced (cold) cracking requires hydrogen, a hard susceptible microstructure, tensile stress, and a temperature below roughly 200°F.

Preheat slows the cooling rate, assists hydrogen diffusion, and lowers heat-affected-zone hardness, reducing cracking risk.

Austenitic stainless steels sensitize between about 800°F and 1500°F by grain-boundary chromium carbide precipitation, depleting chromium locally.

Hot (solidification) cracking is promoted by high sulfur and phosphorus, deep weld pools, and high joint restraint.

Reheat cracking occurs during PWHT in thick low-alloy sections where stress relaxation exceeds the creep ductility of coarse-grained regions.

Lamellar tearing occurs in rolled plate containing inclusion stringers loaded in the through-thickness direction by weld shrinkage.

Duplex stainless welds typically target 35–65% ferrite to balance strength and toughness with chloride stress-corrosion resistance.

PWHT relieves residual stress and tempers hard microstructures; the hold temperature must stay above the tempering range to avoid embrittlement.

RT: denser or thicker material attenuates more radiation; voids transmit more and appear darker, so RT is suited to volumetric discontinuities.

UT detects planar defects such as cracks and lack of fusion and requires a smooth surface, couplant, and trained interpretation of A-scan signals.

MT applies only to ferromagnetic materials and reveals surface and near-surface discontinuities that distort the applied magnetic field.

PT reveals surface-breaking defects in nonporous materials; it cannot detect subsurface discontinuities and requires thorough pre-cleaning.

Visual examination precedes other methods because surface condition, cleanliness, and fit-up affect every subsequent NDE technique.

Portable hardness testing verifies PWHT effectiveness and screens for hard heat-affected-zone microstructures.

Method selection rule: volumetric defects (porosity, slag) favor RT or UT; tight planar defects favor UT, MT, or PT depending on location.

Preheat is verified with a contact pyrometer or thermocouple within a few inches of the joint, on the side opposite the heat source.

Temperature-indicating crayons mark a specific temperature; contact thermocouples or pyrometers provide measured, recordable values.

Backstep welding advances in short segments opposite the general travel direction, spreading heat and reducing distortion and residual stress.

A single-V groove is commonly 60–75° included; excessive bevel angle increases filler consumption and shrinkage.

Distortion control options: balanced welding sequence, presetting, backstepping, minimum number of passes, and judicious restraint.

Low-hydrogen electrodes are held in ovens at about 250–300°F after opening and baked per manufacturer instructions before use.

Fit-up checks cover alignment, root gap, bevel angle, and cleanliness; poor fit-up raises stress concentration and risks incomplete penetration.

Common weld defects include porosity, slag inclusion, incomplete fusion, incomplete penetration, undercut, overlap, and cracking.

Repair sequence: locate the defect by NDE, excavate to sound metal, confirm by MT or PT, reweld with a qualified WPS, then re-inspect.

Toe cracks result from stress concentration plus a hard microstructure; grinding the toe profile reduces the risk of re-initiation.

Chloride stress-corrosion cracking of austenitic stainless steel requires tensile stress, a susceptible alloy, and the specific environment.

A hydrogen bake-out at about 400°F for several hours before PWHT allows hydrogen to diffuse out of thick sections.

Cracking should not be repaired until the cause is established; repeated repairs at the same location may require component replacement.

Temporary repairs are governed by fitness-for-service assessment and require documented engineering approval before implementation.