The full surface of the superheater should be presented for contact with the 

 gases, but the construction must be such as to offer no undue lodging place for 

 the soot and dust that is carried by practically all gases. 



All parts of the superheater should be readily accessible for inspection, 

 cleaning and necessary repairs. The design should be such as to allow freedom 

 of expansion without affecting the boiler proper or the setting. 



All superheaters should be equipped with safety valves set slightly lower 

 than the boiler valves. This is essential to provide a flow of steam through the 

 superheater and prevent any overheating of the superheater in case the load should 

 be suddenly thrown off the boiler or the plant. Safety valves for this purpose 

 should be of the outside spring type, with steel bodies. 



PIPING With moderate degrees of superheat, not exceeding 200 degrees, 

 with properly constructed piping, there will be no greater operating difficulties 

 experienced than with saturated steam. Due to the higher temperatures present, 

 proper care must be taken to allow for pipe expansion in order that there may 

 be no undue strains. This is particularly true in a mixed plant, where super- 

 heated and saturated steam are both used. Under such conditions there will be 

 portions of the piping where the steam at times will become saturated. Such 

 portions will be reduced to the temperature of saturated steam and water will 

 collect. When starting to draw superheated steam through such a dead pipe, 

 due to a sudden increase in temperature, expansion strains will be set up that 

 may lead to ruptured elbows or other connections in the line where proper 

 allowance has not been made for such expansion. 



FITTINGS The question of the proper fittings to be used with superheated 

 steam has been widely discussed. It is an undoubted fact that while in some 

 instances superheated steam has caused deterioration of cast-iron fittings, in 

 others, such fittings have been used with 150 degrees of superheat without 

 difficulty. The quality of the cast iron used for the fittings has doubtless a large 

 bearing on the life of such fittings for this service. The difficulties that have 

 been encountered are distortion and an increase in the size of the fittings, with 

 an eventual deterioration great enough to lead to serious breakage, the develop- 

 ment of cracks, and, when flanges are drawn up too tightly, the breaking of a 

 flange from the body of the fitting. The latter difficulty is undoubtedly due, in 

 certain instances, to the form of flange in which the strain of the connecting 

 bolts tended to distort the metal. 



The Babcock & Wilcox Co. have used steel castings in superheated steam 

 work over a long period and experience has shown that this metal is suitable 

 for the service. There seems to be a general tendency toward the use of 

 steel fittings. In European practice, until recently, cast iron was used with 

 apparently satisfactory results. The claim of European engineers was 

 to the effect that their cast iron was of a better quality than that found in 

 this country and they thus explained the results secured. Recently, how- 

 ever, certain of the difficulties enumerated above have been encountered 



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