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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.
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| |
|
| 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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