MacMillan Bloedel Experience with Stress Corrosion Cracking in CTMP Equipment, 1992 Engineering Conference Proceedings

The predictive maintenance program at MacMillan Bloedel’s Powell River, B.C. mill has required periodic non- destructive examination of chip refiner discs since the early 1980s. Severe cracking has been found in several discs. Cracked discs have either been scrapped or weld repaired depending on the location and extent of the cracking. This paper describes the inspection techniques used and frequency of inspection. Examples of typical disc cracking are given.

Other occurrences of stress corrosion cracking in the Powell River CTMP system are reviewed to place the disc situation in context.

The results of metallurgical examination of scrapped discs are reported. Both stress corrosion cracking and original casting defects have been identified.

Weld repair procedures for cracked discs are reviewed. Since cracking can develop as a result of process changes or simply as a function of time, it is recommended that all TMP/CTMP mills institute formal inspection procedures.