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(a) The tensile strength of different grades of material
shall be within the limits specified in regulation
9 (d).
(b) – The upper yield point at room temperature shall
be not less than 50% of the specified minimum tensile strength
at room temperature.
(c) – The breaking elongation in percentage shall be
not less than ( N-Rm)/C
Where
Rm = Tensile strength at room temperature in kgf/mm2
N
= a quality index of 100 for plate thickness upto 50 mm or
95 for plate
thickness
over 50mm.
C
= 2.2 for only gauge lengths of L=5 do or L=5.65/ ÖAo
Where
Lo
= gauge length
Ao
= original cross section of the rectangular test piece.
do
= original diameter of the round test piece.
NOTE: C= 1.9 for gauge lengths of 4 ÖAo
for test piece of Appendix-B.
(d) – The minimum values of the stress at proof limit
0.2% at elevated temperature (Et) may be calculated by multiplying
the minimum specified tensile strength at room temperature
(R20) by the value of the ratio (Et/R20)
given in the table below:
TABLE
Minimum values for the ratio of the stress at proof limit
0.2% at elevated temperature (Et) to the minimum specified
tensile strength at room temperature (R20) of carbon steel
boiler plates.
| Temperature |
250°C |
*275°C |
300°C |
325°C |
350°C |
375°C
|
| Et/R20 |
0.40 |
0.38 |
0.36 |
0.34 |
0.33 |
0.32 |
| Temperature |
400°C |
425°C |
|
|
|
|
| Et/R20 |
0.31 |
0.30 |
|
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*For temperatures lower than 300°C any test required
for acceptance purposes (in the absence of records of previous
tests at these temperatures) shall be made at 300°C, in
which case the proof stress shall be not less than value obtained
by calculation from the specified minimum tensile strength
at room temperature and the above proof-ratio of 0.36 for
300°C.
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