Porosity is a common defect in the welding of stainless steel pipes, which is manifested as small holes in the weld, affecting the tightness and strength of the pipes. The following is an easy-to-understand way to explain the causes of stomata and how to deal with them:
1. Where do pores come from?
1.1 Gas residue
The metal that melts during welding absorbs surrounding gases (such as oxygen and nitrogen in the air).
If the shielding gas (such as argon) is insufficient or not pure enough, these gases cannot be discharged too late when the metal is cooled, forming bubbles.
1.2 Material is not clean
There is oil, water stains or rust on the surface of the steel pipe, and gas such as hydrogen is decomposed at high temperature and mixed into the weld.
1.3 Improper welding
The current is too large and the speed is too fast: the temperature of the molten pool is too high or the solidification is too fast, and the gas cannot escape.
Wrong Angle of welding torch: the protective gas is blown away by the wind, and the air enters the melt pool.
2. How to avoid air holes?
2.1 Clean well
Clean oil, rust and moisture from the surface of the pipe thoroughly with sandpaper or alcohol before welding.
2.2 Control shielding gas
Argon with purity ≥99.99% is used and the flow rate is maintained at 15-20L/min.
Avoid welding in strong wind environment, which can be shielded by wind hood.
2.3 Adjust welding parameters
Choose the appropriate current (such as 90-120A for 1.2mm welding wire) to avoid excessive current.
Welding speed is uniform, not too fast (8-12cm/min is recommended).
2.4 Select butt welding material
Use a wire containing silicon (Si) or titanium (Ti), such as ER308LSi, to help remove the gas.
Flux-cored wire has better porosity resistance than solid wire.
2.5 Operating skill
Keep the Angle between the welding torch and the workpiece about 75° to ensure that the gas fully covers the molten pool.
The porosity is mainly caused by gas residue and improper operation. By cleaning the material, controlling the gas and adjusting the parameters, you can greatly reduce the porosity and ensure the quality of the welding!
