On Friday, June 26, 2020 at 8:09:00 AM UTC-4, David Spain wrote:
On 2020-06-23 2:49 PM, JF Mezei wrote:
Also, since SN7 was built as a test tank without both tanks or the
engine mounting structures under it, I assume SpaceX are testing new
tank building materials/techniques?


From what I have read elsewhere, yes this appears to have been a
deliberate "test to failure". Apparently SpaceX is experimenting with a
new steel alloy called "304L". Elon was said to have been pleased that
it failed first as a leak before a rupture. They were testing with
cryogenic liquid nitrogen as a prelude to other materials, presumably
liquid oxygen and liquid methane.

Dave

https://futurism.com/the-byte/spacex...-starship-tank
https://www.teslarati.com/spacex-sta...-up-new-alloy/

304L is a slightly modified version of 304 steel. The main difference is that 304L has less carbon, 0.03% as opposed to 0.08% in 304. That means 304L has slightly lower tensile strength and yield strength. But that reduction in carbon means it is easier to weld and gives stronger joints. Interestingly, most metals get stronger as they get colder. An exception is carbon steels as the carbon inclusions provide weak points when the metal is cold. So from that view, 304L is even better than 304.