... -frequency straight seam resitance welding machine, vertical cuts equipment of 1750mm, on-line ultrasonic testing device, off-line ultrasonic ... GB/T3091-2001, GB/T13793 AND SY/T5768 and international standards of API Spec 5CT, API SPEC 5L, ASTM A53, ... standards. All these steel pipes are suitable for the industries of oil, natural gas , shipbuilding , chemical , environmental protection, boiler, ...