"Sewing" a 15" crack would be a terribly expensive job. Every time another threraded plug is added to the line of overlapping plugs there is a possibility for leaks where the plugs meet. That operation is usually used in a combustion chamber where 3 or 4 plugs are installed.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!