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Reg. 58
MATERIALS OF CONSTRUCTION


Material.- (a) Tubes shall be manufactured from steel produced by an open hearth, or electric process or any of the oxygen processes.

(b) Manufacture The tube shall be made by electric resistance welding and heat treated as per the table given below.  In case of cold finished tubes the heat treatment shall be done after the final cold finishing process.

Tube Grade

Heat treatment

WC 1

Normalized* or sub-critically annealed #

WC 2  &  WC 3

Normalized*

* Temperature range                                      800 Deg.C  to  940 Deg.C.

# Temperature range                                      660 Deg.C  to  720 Deg.C.

The tube shall be well finished and free from harmful defects.  The external weld (flash) shall be removed completely i.e. flushed with outside surface.  The internal weld upset shall be trimmed throughout the length of the tube so that the maximum height shall not exceed 0.25 mm.

(c) Chemical Composition.- Ladle analysis of the steel grades shall conform to the following requirements.

Tube Grade

C

      Mn

 

Si

P

S

WC 1     

0.16 max

0.30/0.70

0.35 max

0.040 max               

0.040max

WC 2

0.17 max

0.40/0.80

0.10/0.35

0.035 max

0.035max

WC 3

0.12/0.18

0.90/1.20

0.10/0.35

0.035 max

0.035max

NOTE :1    WC1 grade may be fully killed, rimmed or semi-killed. 

NOTE: 2    For rimmed or semi-killed steel, in case of grade WC1, the C max is 0.19%.

Where the temperature is below 400 Deg. C either rimming, semi-killed or killed steel may be used.  If rimming steel is used, the strips shall be rolled in single width, and not slit longitudinally.

The steel used for design steam temperature above 400 Deg. C shall be of fully killed type.

When ladle analysis is not available the analysis of sample tube selected at random may be used.

(d) Thickness . - The thickness of each tube excluding  the weld shall conform to the permissible variation given below :

Permissible variation (in percent) in wall thickness.

______________________________________________________________

Tube                           Wall thickness                                 _Permissible variation_

Grade                                                                 Over               Under                             _______________________________________________________________

WC1                           3.2 mm and under                               10                            10

WC1                           Over 3.2 mm                                          7.5                           7.5

WC2 &WC3               All                                                            10                            10

________________________________________________________________

The minimum thickness in the weld area shall not be less than that permitted in the body of the tubes. 

(e) Diameter The outside diameter of each tube measured at any position shall conform to the specified diameter within the limits of plus 0.75% and minus 0.75% with a minimum of 0.30 mm over and under.

(f) Length- Unless otherwise specified tube shall be supplied as random length. Where the length is specified as exact length or cut length, the permissible variation shall be + 6mm -0 mm for length up to and including 6 meters.  For every 3 metre increase in length above 6 metres, the positive tolerance shall be increased by 1.5 mm with a maximum of 12 mm.

 
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