*Article* **On the Weldability of Thick P355NL1 Pressure Vessel Steel Plates Using Laser Welding**

**Jiˇrí Capek ˇ 1,\*, Karel Trojan 1, Jan Kec 2, Ivo Cern ˇ ý 2, Nikolaj Ganev <sup>1</sup> and Stanislav N ˇemeˇcek <sup>3</sup>**


**Abstract:** Pipeline transport uses millions of kilometers of pipes worldwide to transport liquid or gas over long distances to the point of consumption. High demands are placed, especially on the transport of hazardous substances under high pressure (gas, oil, etc.). Mostly seamless steel pipes of various diameters are used, but their production is expensive. The use of laser-welded pipes could significantly reduce the cost of building new pipelines. However, sufficient mechanical properties need to be ensured for welded pipes to meet stringent requirements. Therefore, laser-welded 10 mm thick pressure vessel steel plates were subjected to various mechanical tests, including high-cycle fatigue tests. Furthermore, the microstructural parameters and the state of residual stresses were determined using X-ray and neutron diffraction, which could affect fatigue life, too. The critical areas for possible crack initialization, especially in and near the heat-affected zone, were found using different tests. The presented results outline the promising application potential of laser welding for the production of pipes for high-pressure pipelines.

**Keywords:** laser welding; pressure vessel steel; microstructure; X-ray and neutron diffraction; highcycle fatigue tests
