High pressure tubes are used in many industrial applications. Examples are “waterjet cutting” and “hydrogen fuel handling”. In “high pressure application’s”, pressures are handled around 800 bar. The tube dimension 9,53 mm × 3,16 mm is a typical “high pressure” dimension. This dimension can be found in many “waterjet cutting machines”.

Tube is a important component in any “high pressure application”. Tubes are typically used in a fatigue environment. The tube needs to survive a certain number of pressure cycles. It is important to increase the number of “cycles” to extend the lifetime of the tube and as a result, the lifetime of the equipment. Higher lifetime rates greatly reduce planned maintenance and reduce risk of unplanned equipment breakdowns.

The investigation and development to increase the fatigue properties on existing grades (mainly TP316L is this example) is a foundation to the development of a “new high pressure grade” with specific mechanical Properties.

In order to prove the fatigue properties fatigue tests have been carried out under synchronized conditions, using different tubes in comparison grades. In the production of seamless tubes, there are different production methods to create different material properties. Combinations of these methods for each grade are tested and results measured relating to grain size, defect level and surface surface condition are recorded.

The test tubes are produced in different production flow with different surface conditions to develop a comparison between surface conditions and the resulting fatigue related results. Two different grades TP316L and HP120 have been used to prove the test results in combination to material grades.

Different tube samples run on a fatigue test bench. The test pressure is set at 3.000 bar with a sinus curve at 6 Hz.

The results give a development guideline to reach the most advanced tube product for fatigue related applications.

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