... 5. Technique: ERW, hot-rolled6. Certification: CE, ISO7. Material: Q195, Q235, Q345(16Mn), ST37, 20#, Q390, X42 ... steel pipe are widely used in machine-building, construction, metallurgy, automobile-making, railway construction, container support, furniture, decoration and steel ... used in many industries, for instance, steel construction project, machinery making and shipbuilding.structural square tube ...