What is the structure and working principle of sucker rod?

The sucker rod is an important part of the rod pump oil production device. The role of the sucker rod is to connect the upper part of the oil pumping unit and the lower part of the oil pumping pump to transmit power, as shown in Figure . The sucker rod string is composed of several sucker rods connected by couplings.

The sucker rod itself is a solid rod made of round steel, with thick forged heads on both ends, with connecting threads and a square section for a wrench. The external threads of the two sucker rods are connected with a coupling. Common couplings are used to connect equal-diameter sucker rods, and reducing couplings are used to connect variable-diameter sucker rods.

At present, sucker rods are divided into two types from the manufacturing material manufacturers, one is carbon steel sucker rod, and the other is alloy steel sucker rod. Carbon steel sucker rods are generally made of No. 40 or 45 high-quality carbon steel; alloy steel sucker rods are made of 20CrMo and 20NiMo steel. Sucker rods are prone to breakage near the wellhead and threads.

The sucker rod string consists of polished rod and downhole sucker rod. The top sucker rod of the sucker rod string is called the polished rod. The polished rod cooperates with the wellhead sealing box to seal the wellhead.

Conventional sucker rods have simple manufacturing technology, low cost, small diameter, and wide application range. Their utilization rate accounts for more than 90% of rod pump wells. Generally, conventional steel sucker rods are divided into four grades: C grade, D grade, K grade and H grade.

Class C sucker rod: used in shallow wells and light load conditions.

Class D sucker rods: Steel sucker rods used in medium- and heavy-duty oil wells.

Class K sucker rod: Steel sucker rod used in corrosive light and medium load oil wells.

Class K and D sucker rods: Steel sucker rods with the corrosion resistance of K-class sucker rods and the mechanical properties of D-class sucker rods.

Class H sucker rod: Steel sucker rod used in heavy and extra-heavy load oil wells.

Grades A and B are fiber reinforced plastic (glass fiber reinforced plastic) sucker rods: the main material of the sucker rod body is fiberglass reinforced plastic, and a steel joint is installed at both ends of the sucker rod body. The fiberglass sucker rod structure is composed of a fiberglass rod body and steel joints with standard external threads of the sucker rod at both ends. It is light weight, corrosion-resistant, can achieve over-travel, and can be used in medium-sized oil pumping units to achieve deep pumping.