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Reg. 36
MATERIALS OF CONSTRUCTION

COLD DRAWN SEAMLESS CARBON STEEL BOILER, SUPERHEATER AND HEAT EXCHANGER TUBES FOR DESIGN METAL TEMPERATURES NOT EXCEEDING 454°C (850°F).


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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