Resistance welding of pipes — choosing the correct process Which welding process is typically used to join the ends of two pipes or bars of uniform cross-section in a butt joint by heating and upsetting under pressure?

Introduction / Context:
Butt welding of rods, bars, and pipes is common in production of rings, frames, and long products. Resistance-based butt welding processes rely on heat generated at the faying ends and axial pressure to forge the joint.

Given Data / Assumptions:

• Workpieces: pipes/bars with uniform cross-section.
• Objective: end-to-end joining in a butt configuration.
• Power source and force: resistance welding machine capable of upsetting.

Concept / Approach:
In upset butt welding, the prepared square ends are brought into firm contact under pressure; current is passed to heat the interface resistively; then axial force upsets the softened metal to form the bond. This differs from flash butt welding where arcing/flash is deliberately produced before upsetting. Spot, seam, and projection welding are sheet processes with overlapping joints, not end-butt joints.

Step-by-Step Solution:
Identify joint type: butt joint, end-to-end, uniform section.Select resistance process that heats by contact without flashing → upset butt welding.Confirm with mechanism: current + pressure + axial upset → forged joint.

Verification / Alternative check:
Industrial use: chain link fabrication, ring rolling preforms, pipe joining in mills use variants of upset or flash butt welding based on quality and geometry.

Why Other Options Are Wrong:
Spot/seam/projection require lap joints and thin sheet geometry.

Flash butt welding is a related but distinct process involving controlled arcing and flash; the prompt asks the general process used to join ends by heating and upsetting under pressure without explicit flashing, which maps to upset butt welding.

Common Pitfalls:
Poor end preparation causing lack of bond; insufficient upset leading to voids; inadequate alignment resulting in joint offset; not removing the external upset bead if dimensional constraints require it.

Final Answer:
Upset butt welding (resistance heating then axial upset)