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Welding Cleanup Tips: Pre and Post-Process Essentials

Last updated:
April 22, 2024
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Table Of Contents

I. Pre-Weld Cleaning

Before assembly, the surfaces or bevels on both sides of the welding area, ranging from 20 to 50mm, should be cleaned of oil, dirt, embroidery, scale, protective layers, and oxide films to ensure the welding quality of the seam. The common cleaning methods for weldments include degreasing cleaning, chemical cleaning, and mechanical cleaning.

1. Degreasing Cleaning

Before welding, it is necessary to thoroughly degrease the weldments and welding wire of grease and dirt. Otherwise, it will cause defects such as porosity and cracks in the weld. The degreasing cleaning method is as follows:

1) Scrubbing with organic solvents.

For the areas to be welded and the welding wire, if the grease and dirt are minimal and thin, you can use organic solvents such as alcohol, gasoline, dichloroethane, trichloroethylene, and carbon tetrachloride to scrub the grease and dirt. This method is inefficient and labor-intensive.

2) Degreasing in a solution.

Place the greasy or dirty parts of the workpiece and the welding wire into a tank containing a degreasing solution and soak for a certain time to clean off the grease or dirt. Degreasing in a solution is a method of high quality and efficiency, suitable for degreasing plates and welding wires before welding. The composition and degreasing standards of commonly used chemical degreasing solutions are shown in Table 2-25.

Table 2-25 Composition and degreasing standards of commonly used chemical degreasing solutions

Metal materialsSolution CompositionSkimming Specifications
Temperature/℃Time /min
Carbon steel, structural steel, stainless steel, heat-resistant steelNaOH: 90g/L

Na2CO3: 20g/L
Iron, copper, nickel alloyNaOH: 10%. NO: 90%80 ~908 ~10
Na2CO3: 10%. NO: 90%1008~10
Aluminum and aluminum alloysNaOH: 5%. NO: 95%60 ~652
Na2PO4: 40 ~ 50g/L

Na 2 PO 3 : 40 ~ 50g/L

Na 2 SiO 3 : 20 ~ 30g/L
60 ~705~8

① The percentages in the solution composition are by mass.

2. Chemical cleaning

Chemical cleaning mainly involves chemical reactions between the chemical solution and the rust or oxides on the surface of the workpiece and welding wire, forming soluble substances, revealing the metallic luster of the surface of the areas to be welded and the surface of the welding wire. After chemical cleaning, the workpiece and welding wire must be rinsed with hot and cold water to prevent corrosion of the weld by residual chemical solutions. The composition and cleaning standards of commonly used chemical cleaning solutions are shown in Table 2-26.

Table 2-26 Composition and cleaning standards of commonly used chemical cleaning solutions

Metal materialsSolution Composition
(Mass Fraction)
Cleaning RegulationsNeutralizing Solution
Temperature /℃Time /min
Carbon steel heat-resistant alloyHCl: 100 ~ 150mL/L

O: Remaining
First rinse with hot water at 40-50°C, then rinse with cold water
Hot-rolled low alloy steel

Hot-rolled stainless steel

Hot-rolled heat-resistant steel

Hot-rolled high-temperature alloy
SO 4 : 10%

HCl: 10%
54 ~60First, soak the item in a 10% soda solution at temperatures between 60 to 70°C, and then rinse it thoroughly with cold water.
Copper alloy with high copper contentSO 4 : 12.5%

SO 4 : 1% ~ 3%
20 ~77First soak in hot water at 50°C, then rinse with cold water
Copper alloy with low copper contentSO 4 : 10%

FeSO 4 : 10%
50 ~60
Pure aluminumNaOH:15%Room temperature10~15Rinse with cold waterHNO 3 : 30%

(Mass fraction) Room temperature soaking ≤2min
Rinse with cold waterFirst dry at 100 to 110°C, then dry at a lower temperature
NaOH:4% ~5%60~701~2
Aluminum alloyNaOH:8%50 ~605 ~10
Magnesium and magnesium alloys150 to 200 mg/L chromic acid aqueous solution20~407~15Rinse in 50℃ hot water
Titanium alloyHF: 10%

HNO3: 30%

H2O: 60%
Room temperature1Rinse in cold water

3. Mechanical cleaning

Commonly use scrapers, files, emery cloth, metal wire brushes (or metal wire wheels), grinding wheels, and sandblasting to remove rust, oxide layers, and surface protective layers on the surface of weldments near the welding groove. However, for non-ferrous metals and stainless steel, heat-resistant steel weldments, mechanical cleaning is generally only used when local cleaning is needed.

After mechanical cleaning, the end faces and both sides of the weldment to be welded should be wiped with acetone or alcohol to remove residual dirt and grease.

4. Chemical and mechanical cleaning

For large workpieces with long production cycles, chemical cleaning is often not thorough enough, or parts may be contaminated again after chemical cleaning, thus requiring mechanical cleaning of the welding groove area before welding to ensure pre-welding cleaning requirements. Aluminum alloys, titanium, and titanium alloys require immediate welding after cleaning.

5. Permissible time from cleaning of the weldment to completion of welding

After cleaning the surface of the weldment to be welded, welding should be completed as soon as possible to prevent the cleaned surface of the weldment from rusting or oxidizing again during storage, which affects the quality of welding. The permissible time from cleaning the surface to be welded to the completion of welding is shown in Table 2-27.

Table 2-27 Permissible time from cleaning the surface to be welded to the completion of welding

Metal MaterialsWelding MethodsPermissible Storage Time (hours)
Mechanical CleaningChemical Cleaning
CopperFusion welding, Brazing, Spot welding, Seam welding<24<24
Aluminum and Aluminum AlloysFusion welding, Brazing2~3<120
Spot welding, Seam welding<2<72

If the welding is not completed within the specified time, local cleaning can be done mechanically before continuing to weld.

II. Post-weld cleaning

For welded parts that have been completed or have been paused for a long time, it is necessary to promptly remove the welding slag, residual flux, and metal spatter on the welded parts (especially in the weld area) to facilitate visual inspection and non-destructive testing (such as magnetic particle testing, radiographic testing, penetrant testing) of the welds, prevent corrosion of the welds by welding slag and residual flux, and avoid adverse consequences due to the detachment of welding slag and metal spatter during use (especially in moving mechanisms and containers).

Accurately identify welding defects, timely repair welding defects, and eliminate hidden dangers of welding accidents. Common post-weld cleaning methods for welded parts are shown in Table 2-28.

Table 2-28 Common post-weld cleaning methods for welded parts

Metal MaterialsWelding MethodsCleaning MethodsTime Interval from Welding to Cleaning (hours)
SteelFusion WeldingMechanical cleaning (usually sandblasting)<120
Soft SolderingFor water-insoluble fluxes, clean with organic solvents such as alcohol, gasoline, trichloroethylene, isopropanol, etc.

For water-soluble corrosive fluxes and those composed of organic acids and salts, rinse with hot water.

For chlorides of alkali and alkaline earth metals, wash with a 2% HCl solution followed by rinsing with hot water containing a small amount of NaOH.
Hard brazingFor borax and boric acid fluxes, they can be cleaned mechanically; washed in HCl solution; soaked in a 10% H2SO4 solution.

Rinse with hot water or in a 10% hot citric acid solution for borax and flux containing a higher amount of potassium chloride or potassium fluoroborate.
Copper and Copper AlloysBrazingSame cleaning method as for steel welds<24
Aluminum and Aluminum AlloysGas Welding and Arc WeldingAfter scrubbing in hot water at 60-80°C, rinse in a solution of potassium dichromate (K2Cr2O7) or a 2%-3% mass fraction of chromium anhydride (CrO3) solution, then wash again in hot water at 60-80°C and finally dry.Aluminum-Manganese Alloys≤6
Hard Aluminum Alloys≤1
BrazingGenerally, rinsing with hot water is sufficient, but you can also wash in hot water followed by pickling (e.g., 10% HNO3 solution) and passivation.≤1
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