A CRITICAL REVUE OF THE DEVELOPED AND AVAILABLE KNOW HOW DEVOTED TO A SAFE USE OF X100 GRADE STEEL IN LARGE DIAMETER PIPELINES

The increase in natural gas demand in European, North American and Asian countries, foreseen for the immediate future, necessitates the development of cost effective transportation solutions to economically exploit gas fields located in remote area, in some cases 5000-6000 km away from the market regions, across harsh environments. A competitive option of gas to market is represented by the use of high-pressure natural gas transmission pipelines. In particular, for natural gas transportation over long distances, the use of high grade steel (X80, X100 or even higher) large diameter (36" to 56" of outer diameter), high pressure (greater than 15 MPa, that is almost the double of the traditional 8 to 10 MPa) gas pipelines is found to be very attractive and economical. In this context, during the last ten years steel making industries and gas companies have funded fundamental research and development projects dealing with the production and use of high grade steels for gas pipelines; as a consequence, specific know-how and experimental data related with metallurgical design, fracture and deformability behaviour, weldability, etc. of high strength steel gas pipes have been developed and made available to the public. This paper presents a critical revue of the developed and available know how about the production and use of X100 grade steel large diameter gas pipes. Main technical issues related with manufacturing, construction, and operation will be discussed. At the same time issues still open which deserve further investigation will be mentioned, highlighting the more important to fill for a safe use of this new class of steel for near to come high pressure long-distance gas transmission pipelines.