Material selection is typically made by considering the property and process condition of the fluid, and life time requirment. If carbon steel is acceptable material, it is often assumed that it is the most economical material selection. Corrosion allowance is normally added (typically 1 to 3 mm) depending of expected corrosion. Line sizing is often based on maximum allowable pressure drop, wet gas erosion, noise, etc. These criteria are based on experience, but they are not allways well documented.

The material selection, pipe wall thickness determination and line sizing are normally performed by different departments. Individually these departments will seldom possess the required total understanding of which selection parameters are important to arrive at a total economical solution. Therefore it is important to "join forces" at an early stage.

A linesizing and material selection optimization work was recently performed for a major Statoil project resulting in a weight saving of more than 1500 tonnes of piping. The cost reduction was in the order of 50 to 100 million USD. Since then this optimization philosophy has been demonstrated and implemented in several projects with a typical cost reduction of 40 to 50% for the piping systems considered. These solutions typically lead to more use of stainless steels.

As a result of this optimization work, a "new" material has been introduced in some projects that have contributed to an improved total economy, even if the material is expensive based on cost per unit weight. The material introduced is a high strength austenittic stainless steel material, UNS S34565.

Parameters affecting the material selection will be highlighted in this paper. Line sizing, cost and strength of material will be included to some extent to highlight its importance. Finally, some material test results and fabrication experience with the UNS S34565 material will be presented