Steel Plates for Low-Temperature

Steels for Low-Temperature

When designing low-temperature systems or equipment, the engineer finds that notch toughness ranks high in importance, because a part or structure will generally fail due to a notch or other stress concentration. Test results measure the steels capacity to absorb energy, and thus signify its ability to resist failure at points of local stress concentration.

Fatigue limit of steel also must be considered. At low temperatures, systems are usually subjected to dynamic loads, and structural members to cycle stresses. Examples include vessels that frequently undergo pressure changes and large structures and mobile equipment that experience extreme stress imposed by packed snow or high winds. Other considerations include heat conductivity and thermal expansion.

Carbon steels have a better weldability, greater toughness, and higher strenght with low coefficients of termal conductivity than alloy steels. The A 516, one of the most frequently used group of carbon steels, have tensile strengths ranging from 379 MPa to 586 MPa minimum. The big advantage of A 516 steels is their low initial cost.

Compared with A 516, A 442 class have higher carbon and manganese in plates less than 25.4 mm thickness, and lower manganese beyond 25.4 mm. However, applications for A 516 Grades 55 and 60 duplicate those of A 442. They are easier to fabricate than A 442 grades because carbon content is lower.

Higher strength with good notch toughness is available in carbon steels A 537 Grade A and A 537 grade B. Their can be earlier normalized or quenched and tempered to raise yield and tensile strength and impact toughness beyond those of the A 516`s. Table 1 shows mechanical properties at low temperatures for some typical ASTM carbon steels.

Table 1. Specifications for Low-temperature Steels

Designation Lowest usual service temperature, (°C) Min Yield Strength (MPa) Tensile Strength (MPa) Min Elongation, L0= 50 mm (%) Uses
A442 Gr. 55 -45 221 379 – 448 26 Welded pressure vessels and storage tanks; refrigeration; transport equipment
A442 Gr. 60 -45 221 414 – 496 23
A516 Gr. 55 -45 207 379 – 448 27
A516 Gr. 60 -45 221 414 – 496 25
A516 Gr. 65 -45 241 448 – 531 23
A516 Gr. 70 -45 262 483 – 586 21
A517 Gr. F -45 690 792 – 931 16 Highly stressed vessels
A537 Gr. A -60 345 483 – 620 22 Offshore drilling platforms, storage tanks, earthmoving equipment
A537 Gr. B -60 414 551 – 690 22
A203 Gr. A -60 255 448 – 531 23 Piping for liquid propane, vessels, tanks
A203 Gr. B -60 276 482 – 586 21
A203 Gr. D -101 255 448 – 531 23 Land-based storage for liquid propane, carbon dioxide, acetylene, ethane and ethylene
A203 Gr. E -101 276 482 – 586 21
A533 Gr. 1 -73 345 552 – 690 18 Nuclear reactor vessels where low ambient toughness required for hydrostatic testing; some chemical and petroleum equipment
A533 Gr. 2 -73 482 620 – 793 16
A533 Gr. 3 -73 569 690 – 862 16
A543 Gr. 1 -107 586 724 – 862 14 Candidate material with high notch toughness for heavy-wall pressure vessels
A543 Gr. 2 -107 690 793 – 931 14

Since a variety of low-temperature steels are available, the engineer must consider the advantages each has to offer according to the application. The cost-strength ratio is but one factor; others, such as welding and fabrication costs, have equal or greater bearing on final costs. However, heat-treated carbon grades are often used for low-temperature services. Besides offering excellent low-temperature toughness plus fabricability, these grades are lower in initial cost.