| (a) Composition.-
Brass for boiler tubes may be of either 70/30 alloy or 2/1 alloys
as specified.
(b) Chemical analysis.- The tubes shall consist of
an alloy of copper and zinc, and shall contain:-
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70/30 alloy. Not less than 70 per cent of copper and
not more than a total of 0.75 per cent of materials
other than copper and zinc.
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2/1 alloy. Not less than 66.70 per cent of copper and
not more than a total of 0.75 per cent of materials
other than copper and zinc.
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The manufacturer shall supply when required free of
charge, a copy of his works analysis* of the material.
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(c) Freedom from Defects.- The tubes shall be clean,
smooth and free from surface defects or longitudinal grooving,
both internally and externally, and the ends shall be clean
and square.
(d) Tolerances.- The tubes shall be solid drawn and
shall be concentric within the working margins for thickness
given below. The tubes shall be straight and unless otherwise
ordered they shall be of uniform diameter throughout.
The working margins shall be as follows:
On length ± 1/16 inch.
On thickness ± half the difference between the Standard
Wire Gauge (S.W.G.) specified and the next Standard Wire Gauge
thicker.
On external diameter ± 0.005 inch.
(e) All test material shall be annealed before testing and
shall comply with the following mechanical tests:-
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(i)
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Bulging or Drifting
Test.- The test piece shall stand bulging or drifting
cold (see Diagram 1 and
2 respectively) without showing
either crack or flaw, until the diameter of the bulged
or drifted end measures not less than 25 per cent more
than the original diameter of the tube.
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| (ii) |
Flanging Test.-
The test piece shall stand flanging cold (see Diagram
3) without showing either crack or flaw until the diameter
of the flange measures not less than 25 per cent more
than the original diameter of the tube. |
| (iii) |
Flattening and
Doubling over Test.- The test piece shall stand the
following test when cold without showing either crack
or flaw. The rest piece shall be flattened down until
the interior surfaces of the tube meet and then be doubled
over, on itself, that is, bent through an angle 180°
(see Diagram 4), the bend being at right angles to the
direction of the length of the tube.
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(f) Hydraulic Test.- Each tube shall be tested, before
the tubes are presented for inspection, by an internal hydraulic
pressure of 750 lbs. per sq. inch or by such internal hydraulic
pressure as may have been specified by the Inspecting Authority
and the Inspector may re-test 5 per cent or more as he may
deem necessary.
The tubes shall withstand the test without showing any signs
of weeping.
*A Works analysis is defined as the routine analysis taken
by or for the manufacturer in order to control the quality
of the material.
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