Document jmbmRkxXqp72gDxx32bkRDqzk

898 : - 1- ' CHAPTER Sir:. : - ?. 1948 Guide minimum-of-about-3 ppm. JHoweverr even as littleas-3 ppmof dissolved COj can produce .active: corrosion if..large-amounts ofcondensate". are flowing. ,.i.Chemical Treatment ofCondensate. , Condensates containing,compara tively,.Jarge'-amounts ofoil.are.practically non-corrosive,-.due,to the pro tective film providedby the oil. When oil is, intentionally; added to con densate 2i, inadequate quantities -may accelerate rather than.. decelerate corrosion on those surfaces not,Coveredrby the oik. Sodium,silicate added to:CGj-beanng, condensate, has {been shown to, decrease;: but not entirely prevent;, corrosive action.:-. It is. not definite, whether the protection afforded by silicate solutions'is due to the, establishment of;ri protective film pn the meta| surface or to .neutralization 0f.the.Gp2 by .the.aikali in the'silicate solution. 'c (Corrosion and Water Formed Deposits Causes and Prevention 899 - In-contemplating the use of a resistant metal, as a section of a conden sate line, it should, be remembered that, if, other conditions are right, corrosive attack will merely be transferred down stream in the system. Galvanic corrosion resulting from the,contact of dissimilar metals in: a condensate line seldom occurs. No paint or similar, protective coating have thus fUr .ploVen satisfactory; Tests'of cement lined and vitreous lined pipe have; shown the linings to be'readily dissolved by hot con densates. ' ''' '" ATMOSPHERIC CORROSION Most of' the. problems originated by atmospheric corrosion occur,in Connection with the fire side of boilers and furnaces (including their flues and stacks), sewer vents, air ducts, coal, and ash handling equipment; Usually such equipment ^ fabricated from common types of ferrous metals. ' Fig:' 5. Delation of Hydrate/Carbonate 'CoNTENt-iN i/o'r<i:BofLER;WATEft; ;l and COj in Steam at About 5 Psi Operating Pressure: > {Allanalytical values.are:ppm by weight) - . ; . .. ' .... ", !; .It- has: been postulated that'Ammonia M; cyclbhexylamirie " 'etliylenh diamMei.and morpholine27: will retard corrosibn of condensate lines:' Tests' with beri'zylominehavealsdbeen reported 28. 'Where copper andits alloy's are Involved, the use'bf alkaline inhibitors is believed ihadvisable. .The use 0f; small amount's of sodium hexametaphosphate hasbeCn' suggested too,1 but tests 29`indicate that this Salt accelerates'ratHer'thAii decelerates, the rate 'ofattack of ' -steel. by'1 condensate containing CO2 and oxygen. Whether chemical' treatment of'steam or condensate1 is feasible; must be determined not only, upon the basis,of the acuteness of corrosion troubles, but also-upon-,the uses to'which thesteam or.condensate.are put; - '"Use of Resistant Metals. For economic reason's, the:nietals'known to: resist coffpsiori can seldom be used exclusively for condensate linCs hi any' sizeable enterprise. : Nevertheless, there may be instances "where the use of a limited amount of the more costly; but resistant, "materials ca'n' be justified. - The data.in Fig.,6 are the results of. tests30 designed.to reflect the corrosion resistance of the more commonly used metals .to attack by condensate-containing oxygert and-C02- -''Fjg.6, CoMPARAtlVErGoRROSIOn!RESISTl'viTY OF 10 MATERIALS Exposed to Condensate " Generally little or rid' atmospheric corrosion occurs' at temperatures higher than the boiling pointof water, because at such temperatureslittle or no condensate is formed. If it does form at the higher temperatures, only ,,negligible, amounts of carbon. dioxide and oxygen-, present-dn the Atmosphere, will dissolve ifl .the hot liquid but sulphur gases may dissolve arid-cause rapid^attack/ , Oxygeri;isulphur.dioxide, sulphur trioxide, and carbon-dioxide are the "deleterious gases most .frequently accountable for fcorrosiondn moist.atmospheres. :. : -.-.'t t Coal Storage and Handling Equipment ' Virtually all coals contAirl sulphur in the form of pyrite, and some moisture. . .In storage, the pyrite.is likely to be decomposed by oxidizationMoisture dissolves the products of decomposition forming sulphurous.and sulphuric acid. The acid solutions vigorously, attack the supporting.metah Rubber linings have been developed .for coal chutes and: bins-that effectively-resist corrosion and the abrasive action of the coal, but they are. expensive?1..- Concrete,-linings ..for steel bunkers, have also been effectively employed32.