Induction annealing of welded stainless steel tubes has been in practice in some tube mills over the past couple of years. Even now, major annealing operations are carried out in gas fired/electric furnaces with long soaking times. Both processes result in a dull surface finish and, in the latter case, scaling. As a result of this, the tubes need to be pickled and subjected to surface treatments. Induction annealing does result in less scale as the heat-up time is less, but the subsequent water quenching (quenching within the shortest possible time to avoid carbide precipitation) results in a bluish/green finish. Local environment regulations also restrict the installation of pickling plants and hence an alternative system of cooling the tubes in a bright condition has been employed. There is no treatment needed after this process, which has been commercially employed in the heat treatment of stainless steel seamless tubes and is described in detail in the following article.
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