Longitudinally welded large diameter steel pipes are calibrated during the production process in order to meet the pipe tolerances required by the specifications. The higher quality of base materials and the increasing thickness of pipe walls has meant that pipe calibration using standard equipment has become ever more difficult. Furthermore, new pipe material and pipes with high technical requirements such as clad and riser pipes needs a production process designed to produce more precise pipe tolerances to ensure accurate orbital welding on site. In addition, the new orbital welding techniques only achieve satisfying results if limited pipe tolerances are applied.
In order to meet the new requirements of the pipe market, the traditional pipe calibration technique for large diameter steel pipes had to be modified to allow limited pipe tolerances to be produced. The main principle of the Impander® technique is to plasticize the pipe body by regularly upsetting the material until the pipe circumference becomes ideal. In contrast to standard pipe calibration, the Impander® technique produces a constant circumferential pressure, plasticizing the base material and thus making the pipe the optimum circular shape required. Furthermore, residual stress to the pipe is reduced by the Impander®technique. In order to realize this technique, a new machine was developed, patented and named Impander®.
The 4-tool Impander® installed at EBK site Dahlbruch is designed for the following application:
- Force: 4 x 40.000 kN
- Pipe length: 20‘ - 44‘ (6.000 - 13.500 mm)
- Pipe diameter: 14“ - 63“ (355 - 1.600 mm)
- Pipe wall thickness: 0.75“ - 3.15“ (19 - 80 mm)
Longitudinal welded pipes produced applying the Impander® technique (impanded pipe®) have the following advantages compared with conventionally calibrated pipes:
- Tighter tolerances over the whole pipe length even after cutting
- Reduced pipe stress
- Higher pipe collapse resistance