about pre-insulated steel pipes, involving multiple standards such as EN 253, في 448, في 488, في 489, as well as material standards such as API 5L, أستم A53, إلخ. First of all, I need to sort out the specific content and application scope of these standards. According to the information I have searched, في 253 mainly targets steel pipe components of direct buried hot water pipe networks, بينما إن 488 involves steel valve components.