The drill collars are made of forging or finish rolling alloy structural steel per process per API 7 specification. Our advance processing techniques can eliminate regional welding stress concentration and increase life duration, as well as with full length thermal heat-treatment process to ensure the mechanical performances. All DC are inspected to comply with the API standards. These inspections include fluorescent magnetic particle detection and inner ultrasonic flaw detection and hardness detection and mechanical performance detection. Serial numbers and inspection track information are stamped on bar bodies.