MANHOLES, MUDHOLES, ETC.
Raised Manhole Frames and Cover Plates
||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
1 inch thick for pressures not exceeding 120 lbs./sq.
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.
||External raised circular mouthpieces
(1) formed in one piece without welds.
(2) formed from a suitable rolled section and forge welded,
(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.