In general, there are many elements and compounds that […]
In general, there are many elements and compounds that must be eliminated before welding stainless steel grooved pipes. If not removed, the heat generated during welding will cause cracks, welding defects or reduce the corrosion resistance of the weld or heat affected zone. The general sources of elements and elements to purge are:
Sulfur, carbon hydrocarbon: cutting fluid, lubricating grease, oil, wax, primer.
Sulfur, phosphorus and carbon: marking pen, paint and temperature display mark.
Lead, zinc, copper: tools, such as hammers (lead), fixed support rods (copper), zinc rich paint.
Workshop dust: various elements mentioned above.
Sulfur, phosphorus and low melting point metals can cause cracks in the weld or heat affected zone. Carbon or carbonaceous materials left on the surface during welding may be brought into the solution to form a thick carbon layer, which will reduce corrosion resistance in some media.
In addition to general knowledge, there are several principles to be followed in removing the above impurities. Metallic impurities that do not stick to oil or grease are best removed by mechanical means, such as peening or grinding. It is important to ensure that there are no impurities such as free iron on the shot peening material or grinding wheel. After nitric acid treatment, neutralization treatment is also an effective way to remove some low melting point metals. In this way, the stainless steel groove tube will not be damaged.
Oil or grease based impurities (hydrocarbons) must be cleaned with a solvent because they cannot be removed by washing with water or acid water. Usually, large weldments are wiped with a cloth saturated with solvent. Other commonly used methods include soaking, scrubbing or spraying with alkali, emulsifier, solvent, or using the above methods at the same time; degreasing with steam; using steam with or without detergent; or spraying with high-pressure water.
Typical degrees of degreasing or greasing include:
-- wipe off impurities with clean cloth;
-- use organic solvent, such as aliphatic oil, chlorinated hydrocarbon or mixture of aliphatic oil and chlorinated hydrocarbon to scrub the weld area (at least 5cm area on both sides of the weld, only clean solvent (not polluted by acid, alkali or other foreign matters) and clean cloth can be used;
-- use a clean and dry cloth to remove the solvent;
-- check to make sure it is wiped clean.
The residue on the cloth indicates that it has not been cleaned. When the size allows, the fire break test or atomization test is an effective inspection method.