THE USE OF IRON. 69 



has this to say : " The usual market grades of steel plate may 

 be described as follows : Tank steel is the cheapest grade. 

 Us low price is due primarily to the grade of stock used, 

 giving a metal with high percentages of the detrimental 

 elements, even without the careless manipulation which cheap 

 work is so apt to receive. The quality of the tank steel pro- 

 duced by a few makers is sometimes quite good, but experi- 

 ence has shown it to lack uniformity, and good authorities 

 generally agree in condemning its use in important structures. 

 While it may display the physical excellence of the best 

 grades of steel, ' it is apt to be hard and brittle, and should 

 never be used in any part of a stand-pipe.' It is believed 

 by some that a fruitful cause for the treachery of tank steel is 

 to be found in the practice of selling under that classification 

 steel plate which has been rejected from higher grades. It 

 is common to find merely the tensile strength of this grade of 

 steel specified, '60,000 T. S.' being the usual requirement. 



" Shell steel is the next better grade. Its greater excel- 

 lence and enhanced cost are due to the use of more care in 

 selecting the stock and in perfecting the chemical nature of 

 the finished product. Shell steel is used in ordinary boiler- 

 construction, and many stand-pipes have been built from it. 

 It is, of course, preferable to tank steel, but the best practice 

 demands a better grade for high quality boiler and stand-pipe 

 construction. . . Flange steel, the next grade above shell 

 steel, is distinguished by its uniformity, high ductility, and 

 usually low tensile strength. It is the grade of steel plate 

 adopted in. the best practice for the construction of steam- 

 boilers and stand-pipes. . . . Ordinary fire-box and locomo- 

 tive fire-box are still higher grades of steel boiler-plate, pos- 

 sessing special properties which fit them for the uses indicated 

 by their trade designations." 



The matter of cost naturally has a distinct influence upon 

 the selection of grades of materials to be used in stand-pipe 



