OD, ID in Compression. Across Weld At Center - in Tension

The burden of conventional welding is residual stress and stress risers. It is a fact of nature. When molten metal is deposited onto cold steel, no matter how much pre heat, there is an interface where solid meets liquid. Upon solidification heat affected zone. Stress. That is also true of autogenous high energy welding. Friction welding is better but the demand for energy is tremendous. FSW is a different kettle of fish, restricted mostly to aluminum.

A 20 year old technique incorporates off the shelf equipment but arranged in a slightly different order. Result is a weld that has no HAZ, no fusion line, no stress riser. Fine grained base to base. And hardness mapping that is very close to base metal w/ a slight bump at the fusion line. It is one shot, autogenous. OD, ID in compression. Across weld - in tension. Thus 3, 6, 9 and 12 o'clock are in compression. Across weld at center is in tension. Residual stress was verified by Seoul National University using Frontics.

Technique is induction coil between work faces, take to hot working temperature below melting in an inert environment, remove coil, push and turn / shear. Once the work faces are push together, the outsides (OD, ID) begin to cool immediatedly. But the center is still slightly hotter than the outside. When at rest, the center is like a spider web in tension, pulling the outside in.

The advantage of this technique offers resistance to embrittlement, corrosion because the skin is the best protection.

Somewhere between the surface OD / ID and center of the weld, there is a zero, neutral line. But this author has not been able to secure beam time from ORNL to investigate.