welding-field-issues

name	welding-field-issues
description	Welding field troubleshooting — porosity (gas entrapment, hydrogen, nitrogen), hot cracking (solidification/liquation cracking, Varestraint test, carbon equivalent CE), cold cracking/hydrogen-induced cracking (HIC, Pcm formula, preheat calculation, CEIIW), lamellar tearing (Z-direction testing ASTM A770), distortion (angular, longitudinal, transverse), undercut, overlap, incomplete fusion, burn-through, weld spatter, arc strikes, PWHT issues (inadequate temperature, wrong rate, residual stress), weld repair procedures, dissimilar metal welding issues, buttering, cladding defects, ASME IX/AWS D1.1 compliance.
metadata	{"priority":8,"promptSignals":{"phrases":["weld crack","porosity","welding defect","hot cracking","cold cracking","PWHT","weld distortion","incomplete fusion","lamellar tearing"],"minScore":2}}

Welding Field Issues — Complete Troubleshooting Guide

Porosity

Types and Root Causes

Hydrogen porosity: Moisture in electrode coating, flux, base metal, shielding gas → H₂O decomposes in arc → atomic H dissolves in molten weld → as weld solidifies, H₂ solubility drops dramatically → gas bubbles trapped Most common: SMAW with wet/damaged electrodes; FCAW with damp flux core; GMAW with moisture in shielding gas

Nitrogen porosity: Air entrainment in shielding gas → N₂ dissolves in weld pool → bubbles on solidification Cause: shield gas flow too low, cross-wind, wrong cup size, contaminated gas line

CO porosity (carbon steel): High carbon + oxygen → CO gas at high temperature; reacts: FeO + C → Fe + CO Prevention: use deoxidizers (Si, Mn in electrode); insufficient deoxidation → CO porosity

Diagnosis by location: Surface porosity: gas not escaping; too fast travel speed or wrong shielding Subsurface (volumetric): hydrogen from moisture; measure by radiography or UT Wormhole porosity (elongated pores): nitrogen; air entrainment during solidification

Prevention/fix:

• Bake SMAW electrodes: E7018 → 300–370°C, 1 hour before use (ASME IX); store in rod oven at 120°C
• Preheat base metal to >10°C above dew point
• Shielding gas flow: 15–25 L/min GMAW; reduce if wind (use wind shield or increase flow rate)
• Clean base metal: remove mill scale, oil, paint within 25 mm of weld
• Repair: grind out pores to bright metal; re-weld with proper procedure

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Hot Cracking (Solidification and Liquation)

Solidification Cracking

Mechanism: During solidification, liquid film trapped between dendrites; tensile strain (from shrinkage) exceeds ductility of semi-solid → crack along grain boundaries High risk: high sulfur/phosphorus (forms low-melting eutectics FeS, Fe₃P); high carbon; high C:Mn ratio

Carbon equivalent for hot cracking susceptibility: Ito-Bessyo: Pcm = C + Si/30 + (Mn+Cu+Cr)/20 + Ni/60 + Mo/15 + V/10 + 5B UCS (Units of Cracking Susceptibility) = 230C + 190S + 75P + 45Nb − 12.3Si − 5.4Mn − 1 High susceptibility: UCS > 25; low: UCS < 10

Restrastraint test (Varestraint): Controlled bending strain applied during welding → measure total crack length (TCL); threshold augmented strain ε_th below which no cracking Used to rank consumable susceptibility; higher ε_th = more resistant

Field diagnosis: Centerline crack in weld (longitudinal); appears immediately on cooling; visible without NDT on surface; red-end-check test shows crack at high temperature

Solutions:

• Limit heat input: reduces segregation zone size
• Weld bead shape: width/depth ratio W:D > 1.0 (avoid deep narrow beads — worst for centerline cracking)
• Lower S+P in base metal; use low-S filler metal (< 0.008% S)
• Preheat for high-restraint joints (reduces shrinkage stress rate)
• Back-step technique to reduce end-crater cracking

Liquation Cracking (HAZ)

Mechanism: In HAZ, grain boundary liquation of low-melting phases (sulfides, carbides) → liquid films at grain boundaries → tensile stress from weld shrinkage → intergranular crack Most common in: nickel alloys (Inconel 600, 718 — worst), austenitic SS with niobium, some aluminum alloys

Field diagnosis: HAZ cracks, typically 1–3 mm from fusion line; found by PT or MT after cooling; intergranular fracture surface on SEM

Solutions:

• Reduce heat input (limits HAZ width and peak temperature)
• Solution anneal before welding to dissolve grain boundary phases
• For Inconel 718: use Inconel 625 filler (less susceptible); reduce welding current; use pulsed GTAW

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Cold Cracking / Hydrogen-Induced Cracking (HIC)

Mechanism

Three conditions ALL required simultaneously:

1. Susceptible microstructure (martensite; high hardness > HRC 22)
2. Diffusible hydrogen in weld/HAZ (from moisture, contamination)
3. Tensile stress (residual + applied)

Remove any one → no cold crack. Occurs 48–72 hours after welding (delayed cracking).

Preheat calculation (ASME IX / CEN method): Carbon equivalent: CE_IIW = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15 Minimum preheat temperature (AWS D1.1 prequalified): T_p [°C] = 350 × √(CE − 0.25) [Seferian formula; approximate] Or use ASME D-10.8 nomograph with CE, hydrogen level (H4/H8/H16), and restraint level

Hydrogen scale (EN ISO 3690): H4: < 4 mL H₂/100g deposited weld metal (low hydrogen SMAW, baked E7018) H8: 4–8 mL H₂/100g (standard) H16: 8–16 mL/100g (high — not acceptable for > 50 ksi yield)

Field preheat rules (carbon steel SMAW, medium restraint): CE < 0.40: no preheat (t < 20 mm) CE 0.40–0.50: 100°C preheat CE 0.50–0.60: 150–200°C preheat CE > 0.60: 200–300°C preheat

Diagnosis: Underbead cracks (HAZ, parallel to fusion line); toe cracks; root cracks; delayed appearance; transgranular or intergranular fracture; magnetic particle reveals HAZ cracks

Solutions:

• Low-hydrogen electrodes (E7018): baked to manufacturer spec; hermetic containers
• Preheat to calculated T_p; maintain interpass temperature (usually same as preheat min)
• Slow cool or PWHT immediately after welding (hydrogen bake-out: 200–300°C, 1h/25mm thickness)
• Post-weld hydrogen release: hold at 200°C for 4 hours before cool-down (if PWHT not done immediately)

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Lamellar Tearing

Mechanism

Through-thickness tensile stress (from weld shrinkage perpendicular to plate surface) → tears along planar inclusions (MnS stringers from rolling) → step-shaped fracture below weld

Z-direction ductility (ASTM A770): Z-test: tensile specimen pulled through thickness; fracture area reduction (RA_Z) RA_Z ≥ 35%: low lamellar tearing risk (Z35 steel) RA_Z < 15%: high risk; do not use in T-joints with through-thickness stress

High-risk joints: T-joints, corner joints, set-on nozzles, orthogonal stiffeners — any joint pulling through the plate thickness

Solutions:

• Use Z35 or Z25 steel at critical joints (AS/EN 10164)
• Buttering: build up low-strength, high-ductility layer on plate surface before welding T-joint
• Shift fusion boundary: angle weld so it doesn't align with plate mid-thickness
• Replace T-joint with set-through nozzle design
• Use forged nozzle (no inclusions from rolling)

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Distortion

Types and Prediction

Angular distortion (fillet welds): θ ≈ 0.02 × Q / (t × v) [degrees; Q = heat input [J/mm] = V×I/(v); t = plate thickness; v = travel speed] Transverse distortion: Δ_t ≈ K × A_weld / t [K ≈ 0.1–0.2 for butt welds; A_weld = weld cross section]

Root causes:

• Non-symmetric weld sequence
• Inadequate clamping during welding
• Wrong joint fit-up (excessive root gap → more weld metal → more shrinkage)
• High heat input

Control methods: Pre-setting (pre-cambering): plate bent opposite to expected distortion before welding Weld sequence: backstep; balanced welding (symmetric about neutral axis) Strongbacks and fixtures: mechanical restraint Thermal pre-tensioning: flame straightening post-weld Peening (only intermediate passes): compressive stress at weld toe Stress-relief (PWHT): doesn't remove distortion but prevents springback on cut

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PWHT Field Issues

Common PWHT Problems

Insufficient temperature: ASME VIII UCS-56: min PWHT temp for CS = 593°C (1100°F) for t > 38 mm; 593°C for lower thicknesses (different per P-number) Below minimum → residual stresses not adequately relieved → SCC risk in service; HIC risk in wet H₂S Field failure: furnace thermocouple calibration error → actual temp 50°C below setpoint → PWHT credit invalid

Wrong heating rate: Max rate for PWHT: 200°C/h (above 315°C); or 5500/t [°C/h] (t = wall thickness in mm) per ASME Too fast → thermal gradients → thermal stress cracking (especially in thick-to-thin junctions)

Incorrect thermocouple placement: Thermocouples attached to surface (not buried in insulation) → surface reads correct but interior may not reach temperature ASME: thermocouples must be on or embedded in part; soak band ≥ 4× wall thickness each side of weld

Inadequate soaking time: ASME UCS-56: 1h/25mm minimum; not less than 1h Short hold → partial stress relief → high residual stress remains

Re-heat cracking (relaxation cracking): Cr-Mo steels (P91, P22) + PWHT above precipitation temperature → creep + simultaneous strengthening from carbide precipitation → intergranular cracking during PWHT Prevention: ensure PWHT temp is per WPS; avoid temp above upper transformation range for P91 (815°C max)

Sensitization of austenitic SS during PWHT: SS 304: sensitization at 450–870°C (chromium carbide precipitation at grain boundaries → Cr-depleted zone → intergranular corrosion) Never PWHT 304/316 in sensitization range; use stabilized grades (321, 347) or L grades (304L, 316L) if PWHT needed

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Incomplete Fusion / Lack of Penetration

Incomplete fusion (IF): weld metal adjacent but not fused to base metal; planar discontinuity Causes: too-low heat input; incorrect torch angle; incorrect travel speed; wrong groove angle (< 60° for SMAW) Most serious discontinuity: planar → stress concentrator; acts like embedded crack

Incomplete penetration (IP): weld metal doesn't reach root of joint Causes: root gap too small; electrode too large for gap; burn-through risk if gap too large Single-sided pipe welds: target complete penetration; verify by back gouging + RT/UT

Undercut: groove melted into base metal at weld toe not filled by weld metal ASME B31.3: max undercut = 0.8 mm (1/32 in) for t ≤ 25 mm; not permitted at sharp notch angle Fatigue stress concentration at undercut → fatigue crack initiation → especially critical for cyclic loading

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Dissimilar Metal Welding Issues

Carbon steel to stainless steel: Use Inconel 82/182 (ERNiCr-3) filler: prevents carbon migration (decarburization in CS, carburization in SS HAZ) Carbon migration: at service temperature 400–600°C → C migrates from CS to SS → CS side decarburized (weak) → creep failure Buttering: apply 309L SS or Inconel 625 to CS side, PWHT if required, then weld with 309L to SS

Martensitic SS to austenitic SS: Preheat martensitic side (410, 420) to 200–315°C; use austenitic filler (309L); slow cool; PWHT

P91 to P22 or P91 to 304SS: Critical: different PWHT requirements; PWHT P91 = 760°C; PWHT 304 → sensitization Solution: buttering on P91 side at P91 PWHT temp; then weld buttered surface to SS without PWHT

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Arc Strikes

Arc strike: accidental arc contact outside weld zone → rapid local heat cycle → hard martensite → HIC nucleation site ASME B31.3: arc strikes not permitted in pressure-containing welds AWS D1.1: arc strikes not permitted; must be ground and MT/PT inspected; hardness check

Repair: Grind arc strike to bright metal; MT/PT to confirm no cracks; hardness check (< HRC 22 for CS); re-inspect

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Standards

Standard	Scope
ASME BPVC Section IX	Welding procedure qualification
AWS D1.1	Structural welding (steel)
ASME B31.3	Process piping welding requirements
AWS D1.6	Structural welding (stainless steel)
EN ISO 3690	Hydrogen measurement in welds
ASTM A770	Z-direction tensile test for lamellar tearing
NACE MR0175	Sour service material/welding requirements
EN ISO 15614-1	WPS qualification (European)
API 582	Welding guidelines for chemical/petroleum industry

Output

Identify defect type: porosity / hot crack / cold crack / lamellar tearing / distortion / IF / IP / undercut / arc strike / PWHT issue. For each: Porosity: type (H₂/N₂/CO); root cause (moisture/shielding/base metal); size and distribution; acceptable per ASME/AWS? Hot crack: Pcm or UCS; weld bead W:D ratio; recommendation: low-heat-input, wider bead, low-S filler Cold crack: CE_IIW; diffusible H level (H4/H8/H16); T_preheat required [°C]; residual stress condition Lamellar tearing: RA_Z from mill cert [%]; joint type; buttering required? Distortion: measured angle [°]; predicted θ from Q/tv formula; mitigation: pre-camber or fixture PWHT: temp achieved vs. ASME minimum [°C]; rate [°C/h] vs. maximum; soak time [min/mm]; thermocouple placement Repair: grind-out method; re-weld: same or different WPS; re-inspect: MT/PT/UT/RT Applicable code: ASME IX / AWS D1.1 / API 582.