Doc. dr. Matej Pleterski, univ. dipl. inž., Domen Zorko, dipl. inž., oba Numip, d. o. o., Ljubljana;
Izr. prof. dr. Damjan Klobčar, univ. dipl. inž., Univerza v Ljubljani, Fakulteta za strojništvo

Abstract:
When welding stainless steel pipes, it is crucial to assure adequate welding conditions inside the pipe where the root is formed. The weld root characteristics need to be mechanically as well as physiochemically acceptable. Weld root protection is achieved by purging the inside of the pipeline with protective gas. The volume of the purging area is often limited with various types of barriers of which one is water-soluble paper. This type of purging barriers is usually used when there is no possibility to access the inside of the pipeline after welding. Occasional circumstances, i.e. pressure variations inside the pipeline, present a major impact on the purging atmosphere establishment. The present paper shows that the water-soluble paper dams are effective only when there is an atmospheric pressure inside the pipe. Even small pressure differences make use of water-soluble paper dams inappropriate and another purging technique shall be utilized.

Key words:
pipe welding, stainless steel, root purging, water soluble paper