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Contamination on pipe surface.

we are applying 5% Chemetall Oakite 31 (Phosphoric acid) to wash the Carbon Steel pipe (already grit blasted SA2 near white metal finish) at 45 °C temperature after 20 sec of dwell time we wash the surface with DI water (conductivity <20 microseamens. then drying with high pressure compressed air. this time surface is very clean near white metal finish.

Immediately after this we preheat the pipe up to 239-245 °C by Induction Oven. but when pipe somes out of the oven there is dark brown spot and leaves the traces on white paper also. it is like a contamination and it interferes in testing also. Could some one help me to resolve the same.

Yashwant gautam
management - India
December 14, 2009

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