Steel Construction Digest

The American Institute of Steel Construction, Inc., of New York, publishes Steel Construction Digest 6) quarterly which is available without charge to the public. Production and sales data on fabricated structural steel are collected monthly, but these are restricted to members. 

Steel Construction Digest, American Institute of Steel Construction, Inc., New York, quarterly,... 

The sample introduction unit was constructed from inert materials, which minimizes the introduction of metal contamination into the system. The samples or digestion acids make contact only with PTFE, Kel-F, glass, acid-resistant rubber and platinum-iridium (9 + 1) alloy. In addition, the construction materials were Hmited to acid-grade Arborite (ureaformaldehyde laminate). Perspex and stainless-steel. The unit was constructed in three continuous sections a heated sample compartment, a turntable mechanism and heat-exchanger compartment, and a pump compartment. 

Operations using perchloric acid for digestions or heated dissolutions should be performed in perchloric acid hoods that are specifically constructed for this purpose. Perchloric acid, being extremely reactive, can produce explosive perchlorates with metals that are touch- or shock-sensitive. Thus, the interior lining of these hoods must be constructed of nonreactive materials (such as stainless steel) with sealed seams to facilitate decontamination. These hoods are normally fitted with equipment for washing down the interior of the hood exhaust system after perchloric acid use to prevent the buildup of explosive perchlorate residues. The entire exhaust system must be independent of other exhaust systems connected to other chemical hoods. These hoods must be clearly labeled as perchloric acid work only. Anyone using perchloric acid should seek special training in these operations. 

The chromium-nickel-molybdenum steels 1.4571 (SAE 316 Ti, X6CrNiMoTil7-12-2) and particularly 1.4435 (SAE 316 L, X2CrNiMol8-14-3) are resistant to crevice corrosion, which can occur under the operating conditions in a digester if steels with lower alloy contents are used. The importance of the correct constructive design as well as the elimination of welding tarnishes by pickling is discussed [58]. 

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