Welding

Stainless heat tint colours

In short

Tint, temperature reached and backing oxygen: how far is acceptable.

Tint and temperature (304 heated in air)

290 °CPale yellow
340 °CStraw yellow
370 °CDark yellow
390 °CBrown
420 °CPurple brown
450 °CDark purple
540 °CBlue
600 °CDark blue

Indicative temperatures: more chromium delays the tints; longer time, air or a rough surface darkens them. A tint marks an oxide layer and a chromium-depleted surface with lower corrosion resistance (imperfection 610 of ISO 6520-1).

AWS D18.2 chart: oxygen added to the argon backing

1 · 10 ppmBright metal, no tint
2 · 25 ppmBright metal, barely tinted
3 · 50 ppmStraw
Usual limit for hygienic piping.
4 · 100 ppmGolden brown edged with purple
5 · 200 ppmPurple blue
6 · 500 ppmLight blue
7 · 1 000 ppmBlue
8 · 5 000 ppmGrey purple
9 · 12 500 ppmDull grey
10 · 25 000 ppmDark grainy grey

What is accepted

AS/NZS 1554.6 and ASME BPE use samples 1 to 3 (light straw at most) as a guide; from sample 4, a brown, blue or black oxide is rejected on a product contact surface. The specification sets the level; beyond it: pickling, passivation or rework. Compare with the printed AWS chart, not a screen.

Sources

BSSA : teintes de revenu de l’inox chauffé à l’air : Tableau couleur / température, 1.4301 (link)
AWS D18.2:2009 : niveaux de teinte à l’intérieur des tubes inox : Échantillons 1 à 10, ppm d’O₂ (link)
PlantAxiom : soudage hygiénique : < 50 ppm, niveau 3 (link)
ASSDA : résistance à la corrosion et nettoyabilité : Teinte paille pâle maxi sans traitement (link)
AS/NZS 1554.6:2012 (extrait public) : § 6.2.6, tableau 6.3.3 : échantillons AWS D18.2 1 à 3 admis, 4 et au-delà refusés au contact du produit (link)
Kimbrel, Pharmaceutical Engineering : ASME BPE-2009 tableau MJ-3 : échantillons AWS D18.2 1 à 3 (link)

Updated 10 November 2026 · Publisher: The Level Code

Tools · Welding

Heat inputHeat input in kJ/mm (EN 1011-1) from current, voltage and travel speed.Carbon equivalent and preheatCE (IIW), CET and indicative preheat temperature (EN 1011-2, method B) with validity range check.Shielding gasRecommended gas (ISO 14175 class) and flow in L/min by process, material and wire diameter.Back purgeVolume to purge between dams, pre-purge time and gas use to shield the root side.Welding settingsCurrent, voltage, wire or electrode, gas and polarity by process, material, thickness and position; dimensioned joint preparation and passes.Weld shrinkageIndicative transverse and longitudinal shrinkage of a butt joint, with pre-setting advice.Filler metal weightJoint section (V, X, fillet), deposited weight and filler weight to order by process.Weld defect diagnosisTick what you see at the arc, in the pool and on the bead: ranked likely causes and remedies (TWI).ISO 5817 criteriaPermitted limit of an imperfection by quality level B, C or D, and verdict on the measurement (ISO 5817:2023).Weld pass layoutGroove area, number of layers and passes, numbered welding sequence sketch.Dissimilar metal weldingFiller metal to join two different metals (steel, stainless, duplex, nickel, aluminium) and precautions.