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Reg. 572, Reg. 573, Reg. 574

Raised manhole frames, cover plates and joint bolts

 

Raised circular manhole frames not exceeding 16 inches in diameter shall not be less than ¾ inch thick in all parts.

The circular cover plates and joint flanges for such frames shall be not less than-

1 inch thick for pressures not exceeding 120 pounds per square inch.

1- 1/8 inches thick for pressures exceeding 120 pounds per square inch but not exceeding 200 pounds per square inch.

1 ¼ inches thick for pressure exceeding 200 pounds but not exceeding 250 pounds per square inch.

For pressure exceeding 250 pounds per square inch, raised circular manhole frames shall not be fitted.

The cover plates shall be secured by at least sixteen steel bolts not less than 1 inch diameter, such that the stress in the bolts due to steam pressure shall not exceed:-
5,000 pounds per square inch for 1 inch bolts.
6,000 pounds per square inch for 1- 1/8 inches bolts.
6,500 pounds per square inch for 1 ¼ inches bolts.

For the purpose of calculation the pressure shall be assumed to act on the whole area within the pitch circle of the bolts and the bolt area at the bottom of the screw thread shall be taken.



Reg. 573

Stand Pipes and branches-
a) The thickness and bolting of all flanges for joining the mountings  and fittings shall be in accordance with the dimensions as laid down in Appendix- E to these regulations. In no case, however, shall the thickness of flanges be less than 13 mm.
b)
(i) The Wall thickness of nozzles and other connections shall not be less than that specified for the applicable loading, namely, internal pressure, bending and static loads.
(ii) The pressure loading shall be determined by regulation 564, but in no case shall the thickness be less than that calculated by the following formula:-

t = 0.04D + 2.5 mm (equation XII/10)

where, t is the thickness of standpipe and D is the outside diameter of connection. If the branch is connected by screwing, the thickness ‘t’ shall be measured at the root of the thread.
c) Where a double flanged steam pipe is tapered, the thickness of flange joining the boiler and fitting shall correspond to the bore of pipe at the flange connection in accordance with Appendix-E to these regulations.



Reg. 574

Stayed Flat surfaces (other than Crowns of Vertical Boilers).

Stayed heads/ Braced and stayed surfaces.

For various braced and stayed flat plates and those which by these regulations require staying as flat surfaces with braces or stay bolts of uniform diameter symmetrically spaced, the thickness should be calculate by the following formula; namely:-

                                             __________

                        e  =  Cd      P        +   e1

   f1

 


Where,

P=design pressure in kgf/cm²
e=thickness, in mm.
d=diameter of the largest circle taken between staying points of the plate (in mm)
f1=0.85 f (f as defined in regulation 271), kfg/cm²
e1=additional thickness equal to 0.75 mm (0.03 in)
C=coefficient having the following values:-

1) C=0.33 for flanged connections;

NOTE:
d is the diameter of the largest circle taken from the commencement of the curvature of the flange.
2) C=0.40 for stays screwed in plate with nut or screwed and welded, or plain end strength welded on the outside;
3) C=0.33 for screwed bar stays with washer of not less than 3.5 times the diameter of bar stay;
4) C=0.31 for screwed bar stays with reinforcing plate, washer and nut on the outside.

NOTES:
1. If the plate is stayed in any other way, average values of C shall be taken into account.

2. If the plate is flame swept, the thickness shall be increased by 10%.

3. The welding materials used in the manufacture of these plates shall not have the ultimate tensile strength less than that of the plate used.

 
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