Finishing Operations of Cold Worked Tubes

Degreasing / Cleaning

The lubricant used in the cold pilgering process has to be removed completely. If not, the corrosion resistance will be reduced. The tubes are cleaned in hot alkaline. The cleaning is completed by weak acid treatment, rinsing and cleanliness check.

Annealing

Most stainless tubes are delivered in annealed (recrystallised) condition. There are annealing furnaces with open (oxidizing) atmosphere or bright annealing furnaces with a protective gas. Bright annealing is used for tubes in small sizes and tubes destined for special applications. Annealing takes place at 1000-1200°C and is followed by quenching.

Pickling

During annealing in an open atmosphere the surfaces of the tubes are oxidized. This influences the corrosion resistance and the oxide has to be removed. This is done mainly in white-pickling acids.

Straightening/Cutting/Deburring

After annealing the tubes are out of straightness to some degree. By feeding the tubes between inclined rolls they will come out perfectly straight. This operations needs long experience and skill. The straightened tubes are transferred to the automatic cutting device. After cutting, the tubes are transferred for deburring of the ends. All the samples for different material tests are also automatically cut.

Eddy current/Hydrostatic testing

Each tube is checked for leaks either by eddy current testing or hydrostatic testing at a prescribed internal high water pressure.

Ultrasonic testing

In order to guarantee a tube completely free from defects, the tubes can be tested by the ultrasonic method. This method will detect defects both on the outer and inner surfaces and within the tube wall.

Inspection/Marking

Each tube is checked individually for OD and wall thickness dimensions. The inner and outer dimensions. The inner and outer surfaces are also either inspected by Eddy current or optically before marking of the tubes.