168 STEAM BOILERS 



All braces should be inspected by sounding them with a 

 hammer, and if they are attached by cotter pins, it should 

 be seen to that these are firmly in place. All defects found 

 should be marked 1 ; it is good practice to make a memorandum 

 of them as well. If any of the bracing seems to have worn 

 considerably,' it should be measured at the smallest part in 

 order that the safe working pressure thereon may be calculated 

 afterwards. To determine to what thickness a plate attacked 

 by uniform corrosion has been reduced the inspector will have 

 one or more holes drilled through the plate in the worn part to 

 enable him to measure the thickness. These holes are after- 

 wards plugged, generally by tapping out and then screwing in 

 a plug. 



Inspection of Locomotive-Type Boilers. In internally fired 

 boilers of the firebox and locomotive type, particular atten- 

 tion must be paid to the crown bars, crown bolts, and sling 

 stays, and in boilers having the crown sheet stayed by radial 

 staybolts, to these. As a general rule the inspector can make 

 only an ocular inspection of most of them, as they are beyond 

 his reach; where the outer sheets of the firebox contain inspec- 

 tion or washout holes above the level of the crown sheet, a 

 lighted candle tied or otherwise fastened to a stick can usually 

 be introduced through these holes from the outside by a helper. 

 In inspecting above the crown sheet, the inspector should look 

 for mud between the crown sheet and crown bars and sight 

 over the top of the bars to see if any have been bent. As the 

 inspector can reach from the inside of the boiler only a few of 

 the staybolts staying the sides of the firebox, he must rely on 

 the hammer test applied from the inside of the furnace for 

 finding broken staybolts. 



Flues and Combustion Chambers. In boilers having cir- 

 cular furnace flues and internal combustion chambers the top 

 of the furnace flues must be carefully inspected for deposits of 

 grease and scale, which are especially liable to be found if the 

 feedwater is obtained from a surface condenser. Even a light 

 deposit of grease on the furnace flue is liable to lead to over- 

 heating and subsequent collapse of the top. The tops of the 

 combustion chambers, together with their supports, are usually 

 easily inspected, there being ample space to reach every part. 



