The Locomotive . e preventives of corrosion and pitting, and vice versa. Asmall amount of caustic is regarded as a barrier against these last-named boiler ailments, and for that reason is sometimes added to feedwater. There arises, as a consequence, the question as to the doubtfulbenefit of counteracting or removing the caustic to prevent embrittle-ment if by so doing the boiler is to be made prey to corrosion. How-ever, the deciding element in corrosion and pitting is the amount ofdissolved or entrained oxygen in the feed water. If this be drivenout before the water enters the boiler the amou
The Locomotive . e preventives of corrosion and pitting, and vice versa. Asmall amount of caustic is regarded as a barrier against these last-named boiler ailments, and for that reason is sometimes added to feedwater. There arises, as a consequence, the question as to the doubtfulbenefit of counteracting or removing the caustic to prevent embrittle-ment if by so doing the boiler is to be made prey to corrosion. How-ever, the deciding element in corrosion and pitting is the amount ofdissolved or entrained oxygen in the feed water. If this be drivenout before the water enters the boiler the amount of caustic neededto prevent corrosion will not be enough to cause embrittlement. Acompetent feed water chemist will usually be able to prescribe atreatment that will satisfy both conditions. For some reason or other an embrittlement crack does not followwhat is generally considered the line of maximum stress, althoughthe cracks usually proceed from rivet hole to rivet hole in a jagged, 1928. THE LOCOMOTIVE 105. During a hydrostatic test to determine the seriousness of leakage at thegirth scam of a horizontal tubular boiler a trace of salt was found arouiid arivet on the external surface of the rear head. Removal of several rivetsdisclosed caustic embrittlement cracks that affected the head seam throughoutalmost its zvhole circumference. A section of the cracked plate is shozvn above. irregular course. Sometimes two cracks, starting from adjacent rivetholes, will run in a general way parallel to each other, creatingbetween them an island of plate. Very often fine cracks will radiatefrom rivet holes. Proof that the embrittling effect is not present exceptin those parts of the boiler where caustic is concentrated and stressis high is furnished by the observation that cracks never extendbeyond the lap of the plate. Usually the first evidence of embrittlement is a leaky joint thatcannot be made tight in spite of repeated caulking. Further, whitedeposits are frequently found at po
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Keywords: ., bookauthorhartfordsteamboilerin, bookcentury1800, bookdecade1860
