Carbon steel-concrete/cement mortar-stainless steel composite submarine pipeline

A carbon steel-concrete/cement mortar-stainless steel composite submarine pipeline, formed by connecting several composite sub-pipelines arranged sequentially along an axial direction of the pipeline, wherein each composite sub-pipeline has an identical structure and comprises an outer carbon steel pipe and an inner stainless steel pipe, the outer carbon steel pipe and the inner stainless steel pipe each have a circular cross section and are concentrically placed, and concrete or cement mortar is filled between the outer carbon steel pipe and the inner stainless steel pipe to form a sandwiched structure with a circular ring-shaped cross section,

• wherein two adjacent composite sub-pipelines are connected in following mode:
• axial lengths of inner stainless steel pipes of the two composite sub-pipelines at a junction are each beyond the outer carbon steel pipe and the sandwiched structure by a first length, the two inner stainless steel pipes are aligned and welded in a circumferential direction;
• two connecting structures having a length of twice the first length cover outer sides of the two inner stainless steel pipes at the junction respectively, each connecting structure is integrally formed by an inner concrete or cement mortar semi-circular ring and an outer carbon steel semi-circular ring placed concentrically, and an inner side of the inner concrete or cement mortar semi-circular ring contacts the outer side of the inner stainless steel pipe at the junction;
• two outer carbon steel semi-circular rings are aligned and welded in an axial direction;
• and two welded outer carbon steel semi-circular rings and the outer carbon steel pipes of the composite sub-pipelines at two sides are aligned and welded in the circumferential direction.