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Improvement Of Jet Engine Descaling Procedure

Report Number: WADC TR 52-100
Author: Bryan, G. M.
Corporate Author: Northrop Aircraft, Inc.
Laboratory: Materials Laboratory
Date of Publication: 1952-08
Pages: 61
Contract: AF 33(038)-23310
Project: None Given
AD Number: AD0004090
Original AD Number: 4090

X-ray diffraction analysis of the Inconel scale on combustion tube inner liners revealed that it is composed of nickel oxide, the major component, and lesser amounts of chromium oxide and iron oxide. Metallographic examination demonstrated that heavy scale is associated with precipitation, possibly carbides at the grain boundaries, a fact which can explain intergranular corrosion of scaled Inconel in acid solutions. Inconel scale could not be taken off in neutral or alkaline solvents but several acid solutions were found which remove most of the scale without seriously attacking the base metal. Oxidizing pretreatments, particularly with the alkaline permanganate solution in current use by the Air Force, were shown to promote efficient acid pickling. Physical tests of Inconel specimens descaled with the nitric acid-ferric chloride solution revealed that high teiperature pickling (160 deg F) caused a severe loss in tensile strength whereas room temperature pickling caused no appreciable loss in tensile strength. A full scale test of the nitric acid-ferric chloride solution was performed at Norton Air Force Base, San Bernardino, and satisfactory results were achieved.

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