... GB,JIS,ISO,ASTM,BS,DIN the black carbon steel pipe is widely use in conveyor belt transmission,machine rotary ... a trip. you know the rectangular steel pipe is world wide use in construction,goods shelf,steel sheds,truck manufactruing,road construction,fence ... a trip. you know the rectangular steel pipe is world wide use in construction,goods shelf,steel sheds,truck manufactruing,road construction,fence ...