Mechanical Considerations
With regenerative cooling, the pressure in the cooling channels is significantly above the chamber pressure hence the inner liner is under compression, while the outer wall of the engine is under significant hoop stresses.
The metal of the inner liner is greatly weakened by the high temperature, and also undergoes significant thermal expansion at the inner surface while the cold-side wall of the liner constrains the expansion. This sets up significant thermal stresses that can cause the inner surface to crack or craze after multiple firings particularly at the throat.
In addition the thin inner liner requires mechanical support to withstand the compressive loading due to the propellant's pressure, this support is usually provided by the side walls of the cooling channels and the backing plate.
The inner liner is usually constructed of relatively high temperature, high thermal conductivity materials; traditionally copper or nickel based alloys have been used.
Three different construction techniques have been used for regenerative cooling; a corrugated metal sheet is sometime brazed between the inner and outer liner; hundreds of pipes are sometimes brazed into the correct shape, or the inner liner is sometimes milled with cooling channels and an outer liner is used around that.
Read more about this topic: Regenerative Cooling (rocket)
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