抄録
The method of detecting the internal stress in highly stressed Admiralty tubes was studied by using various reagents, such as mercurous nitrate, ammonia and its salts. Investigations were also carried out for the removal of the internal stress and the determination of minimum stress detectable by ammonia treatment. The results obtained are summarised as follows:
(1) Ammonia treatment especially the second method-exposing a small portion of specimen over ammonia solution-is simple, sensitive and more reliable than usual mercury treatment.
(2) The ammonia method is very effective for revealing the direction, distribution, and other several delicate phenomena due to internal stress.
(3) The internal stress of tubes is reduced gradually by annealing; the higher the temperature and the longer the time, the greater is the reduction. Annealing at 400° for 50 minutes the internal stress of Admiralty tubes, whatever its degree, may be released perfectly or at least as safely as that no crack is produced by ammonia treatment.
(4) The stress as low as 3kg/mm2 can be easily detected by ammonia treatment, although the stress less than 8kg/mm2 can not be detected by usual mercury treatment.
Most of the test-pieces used were highly stressed tubes made up by hollow sinking, and others were ordinary tubes finished by plug drawing. As the latter is in a state of very much weaker internal stress than the former, it is ascertained experimentally that internal stress of the latter may be released satisfactorily by annealing at lower temp. (300° 1 hr.) than in the former case.
