TPT January 2014

Article

Steel Plant Specialities

4. Heat treatment of pressure vessels Valve areas of pressure vessels are critical and need to be protected from scaling during thermal cleaning and heat treatment. This is achieved by use of anti-scale coating being applied only on areas where scaling needs to be prevented (Image 3). 5. Salvaging of rejected forgings Re-heating or re-working of forgings is required due to underfill, improper metal formation and similar reasons. However, with stringent dimensional tolerances, there is a risk of components getting scrapped due to excessive scaling (Image 4). Anti- scale coating, when applied on forgings before re-heating for re-working, ensures minimal or no scaling, thereby eliminating risk of scrapping components during re-working (Image 5). 6. Reducing decarburisation during hot forging and hot rolling During hot rolling of special grades of steel where decarburisation needs to be kept in check, unforeseen conditions like mill breakdown and unplanned downtime may

Image 3 : Protection of critical valve areas during heat treatment of pressure vessel. Coating was applied on critical areas that have turned white after heat treatment, with zero scaling

subjected to prolonged heating leading to decarburisation. In both cases, applying an anti-scale coating ensures that billets are protected from decarburisation. (Endorsements 3 & 4)

arise. Even when the plant is closed for weekly holiday, the furnace is shut off abruptly, leaving billets inside the furnace. In these cases, billets or ingots are left in furnace and are

Image 4 : Pit marks formed due to scaling during re-heating for re-working

Summary 1. Use of protective coating has established itself as an effective technique of preventing oxidation and decarburisation during heat treatment, hot forging and hot rolling. 2. It has unleashed a number of additional benefits like ability to salvage by re-heat treatment, elimination of post-heat treatment operations like grinding, shot blasting, acid pickling, etc. 3. The coating process has simplified and accelerated many metallurgical heat treatment operations, saving a fortune in capital investment, reducing costs and improving quality.

Image 5 : Coated with ESPON anti-scale compound before re-heating. No scale pit marks

Steel Plant Specialities – India Tel: +91 22 67978060 Fax: +91 22 25552459

Email: info@steelplantspecialities.com Website: www.steelplantspecialities.com

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January 2014