Nitrogen-hydrogen backing gas
Forming gas nitrogen-hydrogen is used for root-side purging of high-alloy austenitic pipe inner walls to prevent oxidation processes.
Physico-chemical mechanism of action
Forming gas nitrogen-hydrogen consists of a gas mixture of nitrogen and hydrogen. It is used to protect the workpiece from oxidation during forming. The water molecules react with the free oxygen molecules on the metal surface, which prevents the formation of oxide layers.
Metallurgical relevance & risks during welding
When root-side purging of high-alloy austenitic pipe inner walls, forming gas nitrogen-hydrogen can help keep the metal surface cleaner and free of oxides. This improves weld quality and prevents cracks or corrosion in the weld pool. Without this purging, oxide formation and corrosion can lead to hot cracking and other quality problems.
Workshop practice & instructions
Use forming gas nitrogen-hydrogen for root-side purging of high-alloy austenitic pipe inner walls. Make sure that the gas is applied directly to the metal surface and forms a dense layer. The concentration of hydrogen in the nitrogen gas should vary depending on the material and process, but is usually between 5% and 10%. Check the gas supply regularly and make sure that no gaps or bubbles form.