Any steel tube that is used as a barrel for cannon or firearm
must be stress relieved before use. If the barrel should
have residual internal stress buildup due to machining or
manufacture it will be susceptible to low pressure rupture
or shattering. Once stress relieved by heating the barrel
to 525-550 degrees Celsius then allowing it to cool very
slowly to ambient temperature the steel will be very tough
and shatter resistant.
Of course it is possible to strengthen the barrel if desired
by very tightly winding around its exterior a very strong rope
As long as the Black Powder used as a propellant charge isn't
too fast burning or brisant the barrel should be quite safe if
just using it for salutes and not actually firing a heavy projectile.
This Blog has much information on how barrels are manufactured
by the major manufacturers and what steps are taken to make
the barrels very tough.