) Source of evaluation of external coatings
It is pointed out in the literature that the surface condition of steel is called environment. It can be coated and insulated around the soil pipeline. The soil conditions on the surface of the pipeline are different. Therefore, the anticorrosion layer of the pipeline is an important barrier to prevent soil erosion. This is the basic starting point for evaluating the performance of external coatings. Joe Leighton, a British company, has discussed pipeline coating systems from two different perspectives: the European view is that they can withstand moisture and prevent corrosion, which is the "barrier" view. From this point of view, it has a "PE" protection layer method. The North American view is that it has antioxidant, chemical and negative resistance to prevent corrosion, which is the "glue" view. From this point of view, a protective layer of "FBE" law has been created.


Another current trend is to combine the two foreign viewpoints called "barriers" and "bonds" to develop new viewpoints. The forthcoming European "PE" barrier protective layer method and the North American "FBE" protective layer method are combined to develop an integrated "3PE" legal protective layer. Our country's new ideas, new technologies and new methods have begun to be popularized and applied.


(2) Basic Functions of Steel External Coating
There are two aspects:
First, to protect the surface of ERW steel pipe from electrochemical corrosion and bacterial corrosion of basic soil physical media.
Secondly, resistance to creep stress of soil medium movement, static stress and wear strength and structure of basic mechanical protection methods, etc.