Sucker rods are an essential component of rod pump lifting systems. its function is to connect the pump jack at the top and the downhole pump at the bottom, transmitting power. A sucker rod string is composed of several rods connected by couplings.
It is a solid rod made of round steel, with thickened forged heads at both ends, featuring connecting threads and a square cross-section for wrench engagement. The external threads of two rods are connected using a coupling. Regular couplings are used to connect sucker rods of the same diameter, while transition couplings are used for connecting rods of different diameters.
Currently, domestically produced sucker rods are divided into two types based on manufacturing materials: carbon steel and alloy steel. Carbon steel rods are typically made of grade 40 or 45 quality carbon steel; alloy steel rods are made of 20CrMo and 20NiMo steel. they are prone to breakage near the wellhead and around the threaded areas.
The string consists of a polished rod and downhole sucker rods. The topmost rod is called the polished rod, which works in conjunction with the wellhead stuffing box to seal the wellhead.
Conventional Sucker Rod Types
Conventional rods have a simple manufacturing process, low cost, small diameter, and wide applicability, accounting for over 90% usage in rod pump wells. Conventional steel rods are generally classified into four grades: C, D, K, and H.
- Grade C: Used for shallow wells and light-load conditions.
- Grade D: Steel used for medium to heavy-load wells.
- Grade K: used for corrosive light to medium-load wells.
- Grade K, D: Steel rods with the corrosion resistance of Grade K and the mechanical properties of Grade D.
- Grade H : used for heavy to ultra-heavy load wells.
Grades A and B are fiber-reinforced plastic (fiberglass) sucker rods: The main body is made of fiberglass-reinforced plastic, with steel end fittings installed at both ends. Fiberglass rods are composed of a fiberglass rod body and steel end fittings with standard external sucker rod threads at both ends. They are lightweight, corrosion-resistant, can achieve extended stroke, and can be used with medium-sized pump jacks for deep pumping.
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