Late to the party here but..are we certain that there was not some obstruction in that Flues tube? Maybe I've missed something but most of the destroyed shotgun tubes that I've ever witnessed personally (& thankfully not experienced) were caused by a wad or dirt or even snow (which is what wrecked the last 3-inches of my brother's 16 Nitro Special back in the late 1970s).
Embrittlement arguments have been around for a long time and yet they've never been explained in a way for me that is convincing. There are many really old automobiles and even aircraft still in use that would also be subject to this malady and yet they are still in operation.
Actually Lloyd, automotive engineers have determined that steel body panels change over time. Autos are designed with so-called "crumple zones" and other features to absorb the impact from a collision while hopefully keeping the passenger compartment fairly intact. The body panels come out of the stamping press dies with some work hardening which makes them springier. But the engineers have found that some of this springiness dissipates after a few years of driving, probably due to the slight springing and vibration a vehicle endures as it is driven for thousands of miles. Actually, it's just the opposite of becoming more brittle over time, and it is something that can be measured and even seen in the microstructure of the steel.
However, while this is true of the alloys used for auto body panels, it may not hold true for other alloys of steel. I agree with you that the Flues barrel that is the subject of this thread was probably split open due to some sort of barrel obstruction. The relatively thin barrel walls certainly provided a weak point for them to let loose, but the same gun was probably used for a very long time with the same thin barrels, without so much as a slight bulge. If the owner of the gun was available to tell us the barrel split on the first shot after honing out some deep pits, I might feel differently. But a lot of shotguns are being used with even thinner barrel walls in that region. There are a lot of variables, and it is naive to merely blame the failure on wall thickness alone.
