[rout39574]

Think of it like a paper towel tube. It's a spiral.

Single helical weld.

[tlb]

Spiral tube are a bad choice for a rocket. Because rolled steel has the grains largely aligned with the direction of rolling, it is stiffer and has less thermal expansion in one axis than the other. Large forces and temperature changes therefore cause a twisting motion, which can put weird strains on the internal components.

[hinkley]

Pillsbury rolls come to mind. The tube is under pressure from the leavening agent, and you apply torsion on the tub until the can ruptures along the spiral seam.

[ryanmarsh]

That would not go over well with the occupants.

[hinkley]

I recall the rolls scaring the shit out of a fair number of people and those were with the promise of warm, flaky goodness, not hot, fiery death.

This of course matters if the seam is weaker than the rest of the metal.

I've been assured time and again that you can make welds that are stronger than the rest of the metal, but my lizard brain thinks they're all liars.

[mlindner]

They said they would do butt welds, not spiral.