Main causes of Blowhole in submerged arc welding

1. Before filling with pearlite, the water accumulated on the foundation surface of air separation unit must be removed, dried with hot air, and all manholes shall be closed. 2. When filling pearlite, all containers and pipes in the cold box should be inflated and kept at 50kPa pressure, then slightly open the valve of each meter pipeline, and all thermometers should be electrified to check whether the thermometer cable is damaged during the filling process. 3. The filled pearlite shall not be mixed with combustibles. 4. When filling with pearlite, coarse mesh or pearlite pouring device should be set at the manhole on the top of the cold box to prevent whole bag pearlite from entering the cold box. 5. After the pearlite is filled, the manhole shall be sealed.

What is the oxygen extraction rate?