The exhaust pipe coming out of the “tangential tube” is/was in the profile of an “8” without the connection in the center. An engineer friend of mine who looked it over said it makes sense - after the fact - that the exhaust pulses were causing the tube to flex at the center joint.  It appears to have started at the outboard end and went all the way to the center tube and then, perhaps from vibration, cracked out the pipes except for about ½” from the center connection.

 

The main manifold – runners and the tangential tube – are all sound with no signs of stress.

So, be careful out there!

I have several sets of Indy CART turbo race car headers, also Inconel. They were $15.00 a set. They are discarded after three heat cycles. Because they fatigue quickly. They hold strength at very high temps, better than any material. But not very long. They are very thin walled and fail in bending readily.

 

The bends are formed from sheet stock in a die. The two halves are welded together. This is so no stretching of the sheet stock can make it thinner.

 

So no shape that allows pressure pulses to move material around will survive.  The flat end caps will need to be conical or hemispherical. A web must be installed between the pipes.

 

Even a flattened tube end will have to be webbed in several places to last very long at all.

 

The welds are thicker and more stable, so a stress riser forms beside each weld.

 

Or, make it out of stainless.

 

I had made up primary header tubes from .130" wall mild steel tubing. I wrapped the bends with insulation. The outside of the bends turned to dust. Let a little air blow on the same tube bends without insulation, and they last for years. 

 

Lynn E. Hanover