Home | FAQ List


Frequently Asked Questions

Q 30. Which quality of steel should we specify for our tower? What standard should be used ?

Ans : Quality of steel consists of quantitative measures of several different properties / characteristics of steel. End use of steel decides, which property of steel is of importance or relevance for that application. For example, if a chemical reactor is to be fabricated, chemical resistance is of relevance. If steel is to be used as a cutting tool on lathe, then its mechanical strength at high temperature ,involved in cutting, is relevant. In a communication tower, which has been designed to operate within elastic region of steel behavior, the most relevant property of steel is a) Yield Strength of steel. Other properties of lesser importance are
a) Ultimate tensile strength
b) Percent Elongation
c) Chemical Composition
d) Weldability etc. Each country ,depending on
a) Availability of raw materials within that country
b) Availability of production facilities/technologies
c) End use of steel has evolved several standards of steel for each application /end use. Manufacturers of towers everywhere, tend to specify standards of their own country. However, to meet the challenge generated by the situation that manufacturers and end users are from different countries, "International Organization for Standardization" Geneve, Switzerland has been formed.
Certain standards have been finalized by this organization in consultation with member countries. Standard ISO 630, for structural steels, is one of such International Standards. Poly Qual has a policy of specifying "Medium Grade" of steel as per International standard i.e. ISO 630 OR Indian standard IS 2062 for manufacture of towers.
Tabulated at the end as Table 1 and Table 2 are
a) Relevant properties of tower steel for various standards.
b) Range of values for Standards of different countries. As several grades of steel are available, any one grade could be chosen for use in the manufacture of tower. However , the properties of only the chosen grade must be used in the design process. As any grade of steel can be tailored by design process to get the required performance and strength of tower , objective of " Grade Selection Process " is only
a) to keep the total cost minimum for the required performance of tower.
b) To ensure easy availability of desired sections in selected grade of steel If higher value of " Yield Strength " is chosen, then lesser quantity of steel will be required. If lower value of " Yield Strength "is chosen, then comparatively larger weight of steel will be required. Higher value of "Yield Strength" is likely to result in lesser number of gussets, lesser number of holes, faster production and therefore lesser production cost. But the raw material cost of "High Yield Strength" is likely to be high. Availability is also expected to be less, resulting in longer delivery periods. Inspection requirements for high yield strength steel, will go up, because strength of structure will be impaired, if " Yield Strength" is not equal to design value.
Weldability of steels above yield strength of 355 Mpa is questionable. Therefore if welding has been planned in the manufacturing process, it is Desirable to keep the yield strength below 355Mpa. The final decision of selection of grade of steel is governed by
a) Availability of that grade in that country
b) Cost of that grade of steel in that country Needless to say that the availability of a particular grade of steel varies from country to country. Softwares are available, to optimize the amount of "High Yield Strength" and amount of "Low Yield Strength" steel to be used in a tower to get the maximum cost advantage, leveraging the cost differential of two grades of steel.
However, such an exercise becomes useful only when large number of towers are required. A small saving in each tower can result in substantial reduction in total cost of all towers. Conclusion : Standard or Country of origin of steel chosen, has no effect on performance/ strength of tower, as long as the "Yield Strength " of steel used in design is equal to "Yield Strength " of steel actually used for manufacture. International / " or equivalent " standards , whenever specified are likely to result in more competition and better prices for buyer. Please scroll down to next page for tables.
COMPARISON OF VARIOUS STANDARDS FOR TOWER STEELS TABLE - 1 SPECIFICATIONS GRADE OF STEEL
Thickness of Material in mm Minimum Yield Point, Mpa Minimum Tensile Strength,
Mpa max. % C max. % Mn max. % P max. % S max. % Si
BS 4360 40 A <=16 235 340 0.22 1.6 0.05 0.05 0.5
BS 4360 40 A <=19;>16 225 340 0.22 1.6 0.05 0.05 0.5
BS 4360 43 A <=16 275 430 0.25 1.6 0.05 0.05 0.5
BS 4360 43 A <=40;>16 265 430 0.25 1.6 0.05 0.05 0.5
BS 4360 50 A <=16 355 490 0.23 1.6 0.05 0.05 0.5
BS 4360 50 A <=40;>16 345 490 0.23 1.6 0.05 0.05 0.5
ASTM A36 <=38.1 250 400 0.25 1.2 0.04 0.05 0.4
ASTM A283 A <=38.1 165 310 0.14 0.9 0.035 0.04 0.4
ASTM A283 B <=38.1 185 345 0.14 0.9 0.035 0.04 0.4
ASTM A283 C <=38.1 205 380 0.14 0.9 0.035 0.04 0.4
ASTM A283 D <=38.1 230 415 0.14 0.9 0.035 0.04 0.4
API 5A J55 <=6.3 379 517
API 5L A <=12.5 207 241 0.21 0.9 0.03 0.03
API 5L B <=12.5 241 413 0.26 1.15 0.03 0.03
IS 2062 A <=20 250 410 0.25 1.6 0.055 0.055
IS 2062 B <=20 250 410 0.22 1.6 0.05 0.05 0.4
IS 2062 C <=20 250 410 0.2 1.6 0.04 0.04 0.4
IS 8500 Fe440 <=16 300 440 0.2 1.3 0.05 0.05 0.45
IS 8500 Fe440 16-40 290 440 0.2 1.3 0.05 0.05 0.45
IS 8500 Fe490 <=16 350 490 0.2 1.5 0.05 0.05 0.45
IS 8500 Fe490 16-40 330 490 0.2 1.5 0.05 0.05 0.45
IS 8500 Fe540 <=16 410 540 0.2 1.6 0.045 0.045 0.45
IS 8500 Fe540 16-40 390 540 0.2 1.6 0.045 0.045 0.45
IS 8500 Fe570 <=16 450 570 0.22 1.6 0.045 0.045 0.45
IS 8500 Fe570 16-40 430 570 0.22 1.6 0.045 0.045 0.45
IS 8500 Fe590 <=16 450 590 0.22 1.8 0.045 0.045 0.45
IS 8500 Fe590 16-40 430 590 0.22 1.8 0.045 0.045 0.45
ISO 630 E 235 <= 16 235 340-470 0.17 1.4 0.045 0.045 0.4
ISO 630 E 275 <= 16 275 410-540 0.24 1.5 0.05 0.045 0.4
ISO 630 E 355 <= 16 355 490-640 0.2 1.6 0.04 0.04 0.55
RANGE OF VALUES UNDER DIFFERENT STANDARDS TABLE -2
Standard Minimum Yield Strength in Mpa Minimum Tensile Strength in Mpa Min to Max, Min. to Max
American 165 to 379, 310 to 517
British 225 to 355, 340 to 490
Indian 250 to 450, 410 to 590
International 185 to 355, 340 to 640