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Reg. 409

RIVETED STEEL BOILERS

Seating for Mounting

Where the working pressure is not greater than 250 lb./sq.in. mountings have screwed ends not exceeding ¾ inch, standard Pipe Thread may be used.

The mountings may be screwed:

i) Directly into the boiler shell plates, nuts being fitted on the waterside or
(ii)  

Into steel distance pieces (see Fig.35), the length of thread engaged being is no case less than the bore of the mountings plus one quarter inch.

 
That distance piece shall be made solid from mild steel and shall be screwed into the boiler pieces and fitted with nuts on the water side. The walls of the distance plates shall be not less in thickness than one-quarters inch at the bottom of the thread.
 
Method of attachment by welding of connector to sells are shown in Figures 36 to 40.

Water gauges and pressure gauge siphons may be attached direct to the boiler shell or ends without the intervention of a pad or standpipe, provided they are flanged and secured by studs. If the studs are screwed through the plate, nuts of full thickness shall be fitted on the inside of the boiler.

Where the design pressure exceeds 250 lb./sq. in or the nominal bore of the mounting exceeds ¾ inch mountings shall be attached by short standpipes or pads.

Flanges and pads in contact with the boiler shall be formed to bed closely to the plate to which they are attached.

Standpipes:- Where short standpipes are used the flanges shall be machined on the jointing and bolting surfaces and shall bed closely to the plate. The caulking edge of the flange shall be machined or flame cut by machine. Where separate flanges are fitted they shall be attached as shown in Fig 28, 29, 30 and 33.

Standpipes fabricated by fusion welding shall be stress relieved by heat treatment before attachment to the boiler.

Where the outside diameter of a standpipe is not greater than 5 inches plus twice the thickness of the shell plate in inches, the standpipe may be secured by fusion welding in the manner shown in Figures 41-A and 41-B without subsequent stress relieving by heat treatment.

MINIMUM WELD ATTACHMENT FOR STANDPIPES 5 INCH BORE AND UNDER WITH PLATE THICKNESS Ts EQUAL TO 1.5 Tn OR GREATER FIG. 41-A AND 41-B MINIMUM WELD ATTACHMENT FOR STAND PIPES UP TO AND INCLUDING 4 INCH BORE NOT REQUIRING COMPENSATING PLATES 

NOTE: 
TWO TYPES SHOWN A & B ARE REQUIRED ONLY WHERE THE ELECTRODES AND TECHNIQUES TO BE USED HAVE BEEN SHOWN AS SEPARATELY PREPARED TEST SPECIMENS TO GIVE FULL PENETRATION WITH SOUND WELDING AT THE ROOT AND THE GROOVES. 

Where the outside diameter of the standpipe exceeds 5 inches plus twice the thickness of the shell plate in inches, the standpipe may be secured by fusion welding as shown in Figure 42 and 43. The standpipe and the entire plate to which it is attached shall be stress relieved by heat treatment.

Standpipes shall be designed to withstand the internal pressure, but additional thickness may be required for:

(1) Compensation (see Regulation 407).
(2) Stress imposed on the standpipe by expansion and contraction of externally attached pipework.
The thickness of the standpipe shall be not less than ¼ inch or that give by the following formulae, whichever is the greater:
(a) for working pressure up to and including 250 lbs./ sq. in…t = D+4
(b) for working pressure above 250 lbs. / sq. in …t =1.4 D+6
where t = thickness of standpipe in thirty-seconds of an inch.
 
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