The oil casing is composed of a coupling and a pipe body. In order to ensure the function and facilitate transportation, the separate pipe body and the coupling are bolted and transported to the oil and gas field. In order to strengthen the compressive strength and tightening operation of the bolted connection, electric welding is required after the coupling and the pipe body are bolted. Therefore, it is particularly important to analyze the electric welding characteristics of thirty-seven Mn5 and formulate a scientific and reasonable welding method. 

After each technical oil casing and oil layer oil casing is fixed, if concrete does not return to the road surface, a part of oil casing floating in the hole without support point, is free oil casing.  The force of this part of the casing is on the casing that has been sealed.  In manufacturing, the pressure and temperature harm of free oil casing cause the extension of oil casing and the change of internal stress, so it is easy to damage the oil casing.  Therefore, the casing head should be modified after the concrete waiting time is over, in order to seal the annulus between the double oil casing, suspension part of the force of the free section of the oil casing, so that the force is pressed on the surface of the oil casing  

Casing head can be divided into slip type and screw type according to the structure form of suspension oil casing, which consists of oil layer oil casing, technical oil casing and surface oil casing.  A layer of casing head is installed on the top of the surface of the oil casing, connected with the surface of the oil casing pipe thread, casing flange level is basically flush with the road surface.  After the technical petroleum casing is fixed with concrete, part of the hanging weight of the free section is mentioned, and the slips are seated in the cone of the casing head, so that the hanging weight is placed on the cone and the annulus between the double petroleum casing is sealed, and the joint top joint can be removed.