And a few inferior coal are tracheal, conduit intensity on the low side, tube wall is thin, seam welder art backward, seam insufficient rigor, zincic layer is thin, antirust difference.

• 而一些劣质煤气管，管道强度偏低，管壁薄，缝道焊接工艺落后，缝道不够严密，锌层薄，防锈差。