Question: I am designing a structure here in Canada and I am considering the use of steel hollow sections. The structure is exposed to extreme temperature and reversal of forces. As such, one requirement that was imposed by the client was that all structural steel shall be Grade 350WT comply with Charpy Test requirement of 20 Joules at -20 deg. Celsius. Grade 350WT has a minimum yield strength of 350 MPa (or 50 ksi) and tensile strength of 450 to 620 MPa (or 65 to 90 ksi). Appreciate if you could advise whether such HSS material is readily available in North America.

Answer: The specification of a notch tough steel for a cold, dynamic application is very wise, and CSA G40.20-13/G40.21-13 Grade 350 WT Category 2 seems to have been specified. (Category 2 corresponds to 27J at -20°C, whereas you have actually stated 20J, which is a slightly lesser requirement. Normally 27J is the stipulation in Canada, per Table 9(b) of the CSA “Structural Quality steel” standard). Grade 350W/50W is readily available in Canada (although ASTM A500 comprises around half of the national market), but the notch-tough WT grade may need to be ordered from a tube producer as it is a special requirement. 

There is another grade of HSS now produced in North America since mid-2013: ASTM A1085. This has superior structural properties to ASTM A500 and could be substituted for CSA G40.20/G40.21 Grade 350 WT Category 1. (Category 1 has a minimum Charpy V-Notch toughness of 27J at 0°C, whereas ASTM A1085 has a minimum Charpy V-Notch toughness of 34J at 4°C). If a HSS supplier suggests using ASTM A1085 material then you would have to invoke a supplement S2 add-on, which allows a special, more stringent, Charpy V-Notch toughness to be specified.  However, since your project is in Canada you may as well stick with CSA G40.20/G40.21 Grade 350 WT Category 2 material.