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1. Scope  This Japanese Industrial Standard specifies high tensile strength steel tubes (gerefter referred to as "tubes") used principally for transmission steel tower.
Remarks 1. The purchaser may specify the special quality requirements specified in Annex in addition to the items specified in this text in the case or STKT 590 by preliminary agreement between the purchaser and manufacturer.
        2. THe standards cited in this Standard are given in Attached Table 2.

2. Classification and symbol The tubes shall be categorized into two classes, and their symbols shall be as given in Table 1.

                                                     Table 1  Classification and symbol

* World standard Comparative Table

3. Method of manufacture The manufacturing method of the tubes shall be as follows :
  (1) The tubes shall be manufactured by electric resistance welding or electric are welding(straight seam).
  (2) The tubes shall be supplied as-manufactured conditions and, as a rule, shall not be heat-treated.
           
4. Chemical composition The tubes shall be subjected to the test of 9.1, and the cast analysis value thereof shall be as given in Table 1.

                                                   Table 1  Chemical composition
                                                                                                                      

Unit:%

Symbol	C	Si	Mn	P	S	Nb+V
STKT 540	0.23 max.	0.55 max.	1.50 max.	0.040 max.	0.040 max.	-
STKT 590	0.12 max.	0.40 max.	2.00 max.	0.030 max.	0.030 max.	0.15 max.

Remarks 1. Alloy elements other than those given in Table 1 may be added, if necessary.
        2. The tubes of STKT 590 shall be of fine grain killed steel up to and including 25mm in wall thickness.
  
5. Mechanical properties

6. Carbon equivalent The carbon equivalent for the tubes shall be 0.40 % or less. The carbon equivalent shall be calculated from the following formula by using the cast analysis values given in 9.1.
              Carbon equivalent (%) = C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14

7. Dimensions, mass and dimensional tolerances

8. Appearance The appearance of the tubes shall be as follows :
 (1) The tubes shall be practically straight, and the both ends thereof shall be at a right angle to the axis of the tubes.
  (2) The tubes shall be free from defects that are detrimental to practical use.
  (3) When especially required, the surface finish of the tubes shall be agreed upon between the purchaser and manufacturer.

9. Test
 
10. Inspection
 
11. Making The tubes which have passed the inspection shall be marked on each tube with the following items provided that the order of arranging the peculiarities is not specified. However, in the case of either smaller tubes or on request by the purchaser, the tubes may be bundled together and marked for every bundle by suitable means.
Futher, when approved by the purchaser, a part of the items may be omitted.
  (1) Symbol of class
  (2) Symbol indicating method of manufacture(¹)
  (3) Dimensions
  (4) Manufaturer's name or identifying brand
  (5) Symbol Z denoting the special quality requirement
       Note(¹)   The symbol indicaing the method of manufacture shall be as follows, provided that the dash may be replaces by a blank.
                 Electric resistance welded steel tube :-E-G
                 Electric arc welded steel tube    :-A
12. Report When preliminarily requested by the purchaser, the manufacturer shall submit  the test results report