Cold Work Influence on Subcritical Crack Propagation in Downhole Tubing
Cold work elevates downhole tubing dislocation density and residual tensile stress, sharply reducing K_ISSC thresholds and accelerating subcritical cracking.
Cold Pilgering
Meaning
Longitudinal rolling processes that use ring dies and a tapered mandrel reduce the diameter and wall thickness of metal tubes. The use of cold pilgering allows for high cross sectional reductions in a single pass while improving the surface finish of the pipe. This method is particularly effective for processing hard alloys like stainless steel and nickel superalloys.
It produces tubes with precise dimensions and a refined grain structure.
Mechanical Reduction
Force is applied by a pair of grooved rolls that move back and forth over the tube. During cold pilgering, the tube is fed forward and rotated between strokes to ensure uniform deformation. This complex movement distributes the strain evenly and prevents the formation of internal defects.
The reduction in area can reach over seventy percent for certain materials, which minimizes the number of processing steps required.
Surface Quality
Smooth finishes on both the internal and external diameters result from the high pressure contact with the tooling.
Throughput Efficiency
Production rates depend on the stroke frequency and the feed rate of the machine. While cold pilgering is slower than simple drawing, it offers better control over the final mechanical properties of the tube. The cost of the specialised dies and mandrels is offset by the reduction in material waste and the elimination of intermediate annealing cycles.
Manufacturers use this process to produce high performance tubing for aerospace and nuclear applications.