What should be done at the steel pipe interface to make the insulation better

Generally speaking, the steel pipe like seamless steel pipe and ERW steel pipe for oil exploit would have good heat insulation with the withstand of high temperature of 120°C. Of course, it can reach at 180°C through modification or combination with other insulation materials, which would be better for heating pipeline applications.

Here is the question: What should be done at the steel pipe's interface to make the insulation better?

Trying to complete as many welding holes as possible on the ground first, and then drop the pipe in the buried trench. Due to the difficult flip, there should be dig before installation. At present, domestic units also use automatic welding machines, which can greatly reduce the welding strength and improve the welding quality.