| (i) |
General.- The provisions of
this regulation apply to both Hot Finished and Cold
Drawn Seamless Boiler and Superheated Tubes which shall
conform in all respects with the requirements herein
specified.
|
| (ii) |
Material.- The tubes
shall be manufactured from steel produced by the Open
Hearth or Electric process or any of the oxygen processes
and shall conform to the following limits of chemical
composition:- |
| |
Carbon |
0.15% maximum |
| Manganese |
0.30% to 0.70% |
| Silicon |
0.1% to 0.50% |
| Phosphorus |
0.04% maximum |
| Sulphur |
0.04% maximum |
| Chromium |
1.90% to 2.6% |
| Molybdenum |
0.87% to 1.2% |
| |
The Steel maker shall prove to the satisfaction
of the Inspecting Authority that the quality of the steel
is of the required high temperature Creep Strength.
|
| (iii) |
Heat Treatment.-
The tubes shall be fully annealed or normalised and tempered,
at a temperature approved by the inspecting Authority. |
| (iv) |
Workmanship and tolerance.-
The tubes shall be well finished, clean and free from
harmful defects. They shall be reasonably straight, smooth,
cylindrical and subject to the following tolerance before
bending. |
| (a) |
Diameter.- The external
diameter of the tubes measured at any point shall be within
the following tolerances of the diameter specified:-
|
| |
Type of Tube
|
Outside Diameter of Tube
|
Tolerance
|
Hot finished
|
Upto and including 64 mm (2½ inches)
|
+0.4mm (1/64”)
-0.8mm
(1/32”) |
Hot finished
|
Over 64 mm (2½ inches)
|
+1%
-1% |
Cold drawn
|
All sizes
|
+0%
-1% |
|
| (b) |
Thickness.- The thickness
of the tubes shall be within the following tolerances:-
|
| |
| Type of Tube |
Outside Diameter of Tube |
Tolerance |
Hot finished
|
Upto and including 64 mm (2½”)
---------------------------------------------
Over 64 mm (2½”)
|
+17½%
-7½%
----------------
+15%
-5%
|
Cold drawn………………
|
All sizes
|
+10%
-5% |
|
| |
Where the ends of the tubes are swelled
or reduced, the thickness at the ends may be decreased
below or increased above the nominal thickness of the
tubes by an amount in proportion to the percentage of
such swelling or reduction, and in addition to this allowance,
the tolerances relating to thickness shall also apply.
Swelling or reduction shall be carried out before the
heat-treatment specified in Regulation 56A (iii).
|
| (c) |
Length.- The tubes shall be not less
than the nominal length but may exceed it by the amount
given below:-
Upto and including 9 metres (30 ft.)……………3
mm (1/8”)
Over 9 metres (30 ft.)…………………………...6
mm (1/4”)
|
| (v) |
Selection of tubes for testing.-
After heat-treatment, the tubes shall be presented for
mechanical testing in accordance with the Regulations
56A(vi), 56A(vii)
and 56A(viii),
in batches of not more than 100 of the same nominal diameter
and thickness. The manufacturer shall provide at his own
expense extra tube at the rate of 2 per cent, of each
diameter and thickness of tube specified and the Inspecting
Officer shall select for test such of the tubes as he
may think proper to the extent of the percentage mentioned.
Should the number of tubes specified of any one nominal
size exceed 400, then, for every 100 tubes or part thereof
above that number, one additional tube shall be provided.
The samples for testing shall not be heat treated after
selection.
|
| (vi) |
Tensile Test.- Test
pieces cut from the ends of the selected tubes shall comply
with the following requirements:-
The tests may be carried out on test pieces cut out
from the tube in the longitudinal direction which shall
not be further heat-treated nor straightened within
the gauge length. As an alternative, tubes may be tested
on full cross section.
|
| |
Kind of Steel
|
Tensile strength minimum
|
*Elongation on
|
|
kg./mm2
|
Tons/sq. inches |
Lo = 5do or
Lo = 5.65 (A)1/2
% minimum |
Chromium Molybdenum Steel
|
39
|
25 |
20 |
|
| |
Notes:
Lo = original gauge length
do = original diameter; and
A = original area of cross section
|
| (vii) |
Flattening Test.-
A ring not less than 51 mm (2 inches) in length cut from
one end of each selected tube shall be flattened between
two parallel flat surfaces, the width of which shall be
not less than 1½ times the diameter of the tube.
When the pressure is released, the interior surfaces of
the test pieces (at the middle) shall remain at a distance
apart of not more than three times the specified thickness
of the tube and the test piece shall then show no sign
of crack or flaw.
Flattening test carried out in accordance with any
other standard code may be accepted in which case, the
Code adopted shall be specified.
|
| (viii) |
Expanding Tests.-
The tubes shall withstand expanding by a drift expander
having a total included angle of between 40° and 60°
(20° and 30° per side) to the following increases
in external diameter without showing crack or flaw:- |
| |
Thickness of Tube
|
Increase in Diameter per cent |
3 mm (0.128”) and thinner………………………….
|
12½ |
Thicker than 3 mm (0.128”) upto
and including 5 mm (0.192”)……………………………………………….
|
9½
|
Thicker than 5 mm (0.192”)…………………………
|
6½
|
|
| |
In lieu of expanding test as
above, flaring test carried out in accordance with any
other standard code may be accepted in which case, the
Code adopted shall be specified.
|
| (ix) |
Additional tests before rejection.-
Should a tube selected for testing purpose show definite
signs of failure in any one or more of the tests specified
in clause (vi), (vii) and (viii) two further tests of
the same kind may be made at the option of the manufacturer
from two additional selected tubes. If the repeat tests
are satisfactory, the tubes shall be accepted provided
that in all other respects they fulfill the conditions
of these Regulations. Should either of the tubes fail
in any test, the batch of tubes represented may be re-heat-treated
in accordance with clause (iii) and then re-tested in
accordance with clauses (vi), (vii) and (viii) but employing
twice the number of test pieces.
If the second repeat tests are satisfactory, the tubes
shall be accepted provided that in all other respects
they fulfill the conditions of this standard; but if
definite defects are again shown, the batch of tubes
which the test pieces represent shall be rejected.
|
| (x) |
Each tube shall
be tested at the Makers’ works and shall withstand
a hydraulic pressure of 1½ times the design pressure,
subject to a minimum of 70 kg./sq. cm2 (1000 lbs. per
square inch). |
| (xi) |
Notwithstanding
anything contained in sub-regulation (x), the hydraulic
test for tubes in makers’ premises shall be dispensed
with by the Inspecting Authority provided that the tubes
are subject to non-destructive testing by an appropriate
method like ultrasonic or/and Eddy current testing. |
