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36.(a)
General.-
(i) These regulations cover both hot finished and cold drawn
seamless boiler, superheater and heat exchanger tubes, which
shall conform in all respects with the requirements herein
specified.
(ii)The
seamless tubes conforming to other national or international
standards which are known to be commonly used as being
suitable for use as boiler, superheater and heat exchanger
tubes can also be used with the designations of the national
or international standards, provided such materials are not
specifically prohibited by the regulations.
(iii)
While making tubes to other national/international
standards the allowable stresses of the respective standards
shall be strictly followed while designing the tubes.
(b)
Material. -
(i)The tubes shall be seamless and manufactured from steel
produced by an open hearth or electric process or any of the
oxygen processes. The steel shall be fully killed.
(ii)The
steel shall conform to the following limits of chemical
composition.
Chemical
composition (%)
|
Grade
|
C
|
Mn
|
Si
|
S
|
P
|
|
TA
|
0.06-0.18
|
0.27.-0.63
|
0.25
max
|
0.035
max
|
0.035
max
|
|
TB
|
0.27
max*
|
0.93
max
|
0.10
min
|
0.035
max
|
0.035
max
|
|
TC
|
0.35
max*
|
0.29-1.06
|
0.10
min
|
0.035
max
|
0.035
max
|
*
For grade TB and TC for each reduction of 0.01% below the
specified carbon maximum, an increase of 0.06% Manganese above
the specified maximum will be permitted up to a maximum of
1.35%.
(c)
Heat Treatment.- Hot
finished tubes need not be heat treated, cold drawn tubes
shall be given a sub-critical
annealing, a full anneal, or a normalising heat
treatment after the final cold finishing process.
(d)
Workmanship and Tolerance.-The
tubes shall be well finished, cleaned free from harmful
defects. They
shall be reasonably straight, smooth, cylindrical and subject
to the following tolerances.
Finished tubes shall be reasonably straight and have
smooth ends free of burrs.
They shall have a workmanlike finish.
Surface imperfections like any discontinuity or
irregularity found in the tube may be removed by grinding,
provided that smooth curved surface is maintained, and the
wall thickness is not decreased to less than that permitted.
The outside diameter at the point of grinding may be
reduced by the amount so removed.
(i)
Permissible variations in outside diameter.
|
Outside
Diameter (mm)
|
Permissible
variation
Over
(mm)
|
Permissible
variation Under
(mm)
|
|
Hot
finished seamless tubes
|
|
101.6
and under
|
0.4
|
0.8
|
|
Over
101.6 to 190.5 incl.
|
0.4
|
1.2
|
|
Over
190.5 to 228.6 incl.
|
0.4
|
1.6
|
| Cold
finished seamless tubes
|
|
Under
25.4
|
0.1
|
0.1
|
|
25.4
to 38.1 incl.
|
0.15
|
0.15
|
|
Over
38.1 to 50.8 excl.
|
0.2
|
0.2
|
|
50.8
to 63.5 excl
|
0.25
|
0.25
|
|
63.5
to 76.2 excl.
|
0.3
|
0.3
|
|
76.2
to 101.6 incl.
|
0.38
|
0.38
|
|
Over
101.6 to 190.5 incl.
|
0.38
|
0.64
|
|
Over
190.5 to 228.6 incl.
|
0.38
|
1.14
|
(ii)
Permissible variation in Wall Thickness in percentage.
|
Outside
diameter
(mm)
|
Wall
thickness (mm)
|
|
2.4
and under
|
Over
2.4 to 3.8
Incl.
|
Over
3.8 to 4.6 incl.
|
Over
4.6
|
|
|
Over
|
Under
|
Over
|
Under
|
Over
|
Under
|
Over
|
Under
|
|
Seamless
Hot Finished tubes
|
|
101.6
& under
|
40
|
0
|
35
|
0
|
33
|
0
|
28
|
0
|
|
Over
101.6
|
NA
|
NA
|
35
|
0
|
33
|
0
|
28
|
0
|
|
Seamless
Cold Finished tubes
|
|
|
Over
|
Under
|
|
38.1
and under
|
20
|
0
|
|
Over
38.1
|
22
|
0
|
| |
|
|
|
|
|
|
|
|
|
(iii)
Permissible variations in length
|
Method
of manufacture
|
Outside
diameter (mm)
|
Cut
length (mm)
|
|
Over
|
Under
|
|
Seamless
hot finished
|
All
sizes
|
5
|
0
|
|
Seamless
cold finished
|
Under
50.8
50.8
and over
|
3
5
|
0
0
|
Note.-
These permissible variations in lengths apply to cut lengths
up to and including 7.3 m.
For lengths over 7.3 m, an additional over tolerance of
3 mm for each 3 m or fraction thereof, shall be permissible, up to a
maximum of 13 mm. Length
tolerances on the positive side other than specified may be
mutually agreed.
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