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A new upper shaft of a vertical ammonia transfer pump failed after 2000 hours of service. The new
upper shaft material was AISI 410 martensitic stainless steel and replaced the original shaft made
from AISI 4140 HT chromium-molybdenum steel while the lower shaft still in original condition.

A new upper shaft of a vertical ammonia transfer pump failed after 2000 hours of service. The new
upper shaft material was AISI 410 martensitic stainless steel and replaced the original shaft made
from AISI 4140 HT chromium-molybdenum steel while the lower shaft still in original condition. It was
broken into four separated pieces with different fracture modes. The failed shaft was examined and
tested by various methods. The result of the analysis indicated that the shaft failed by the improper
mechanical properties specification of new shaft material. The hardness and yield strength of the new
material were about 50% below the original material specification. In addition, these low hardness and
yield strength were resulted from non heat treatment condition confirmed by metallography
examination that revealed the anneal structures of shaft material. It is recommended that shaft
material must be heat treated first to produce tempered martensite structure with hardness minimum
280 BHN.

Key words: Shaft Failure, Martensitic Stainless Steel

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