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Reg. 167
MANHOLES, MUDHOLES, ETC.

 

Raised Manhole Frames and Cover Plates

a) Raised circular manhole frames not exceeding 16 inches in diameter shall be at least ¾ inches 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 lbs./sq. inch.

1 1/8  inch thick for pressures over 120 lbs. but not exceeding 200 lbs./sq. inch.

1¼ inch thick for pressures over 200 lbs. but not exceeding 250 lbs./sq. inch.

For pressures 250 lbs./sq. inch and over 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.

b) External raised circular mouthpieces shall be:

(1) formed in one piece without welds.

(2) formed from a suitable rolled section and forge welded, or

(3) fabricated by fusion welding provided they are stress relieved by heat treatment after welding and before attaching to the boiler.

Welds should be positioned so that they are located on the transverse centre line of the boiler. The jointing flanges of mouthpieces and covers shall be machined on the face and edge and on the bearing surface for the bolts.

Bolts and nuts shall be machined where in contact with the flanges and the joints should be formed inside and outside the bolts to preclude the possibility of flange distortion. Cover plates shall be dished outwards to a depth of approximately one-eighth of the internal diameter of the frame.

All frames and mouthpieces shall bed closely to the surfaces to which they are to be connected, and where riveted to cylindrical shells shall be at least double riveted. All caulking edges shall be machined or machine gas cut.
 
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