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The sucker rod is a slender component used in pumping wells, connecting the polished rod at the surface to the downhole pump. It serves as a critical link for transmitting mechanical power from the surface unit to the submersible pump. Typically, each individual sucker rod has a length of 7.62 meters, 8 meters, or 9.14 meters, and is made from low-carbon alloy steel that undergoes quenching and tempering treatment to enhance its strength and durability. These rods are joined together using internal-thread couplings, extending deep into the wellbore—often reaching depths of up to two kilometers, with some wells, like those in the Shengli Oilfield, going over three thousand meters deep.
As a vital part of the rod-pumping system, the sucker rod string consists of dozens or even hundreds of individual rods connected by couplings. During operation, the string experiences asymmetric cyclic loads due to the reciprocating motion of the pump. Additionally, it is exposed to well fluids such as crude oil and produced water, which may contain corrosive elements. This environment makes fatigue fracture and corrosion fatigue the most common failure modes. When a sucker rod breaks, it can significantly disrupt production, increase workover costs, and raise overall operational expenses.
Sucker rods have a long history, dating back nearly a century. The earliest versions were made from natural materials like rattan. The first metal sucker rod patent (U.S. 528168) was granted to Samuel M. Jones of Ohio on October 30, 1894. Over the past two decades, significant advancements have been made in their manufacturing, including the use of multi-element alloy steels and fiber-reinforced polymers. Modern techniques now include forging, intermediate frequency induction heating, quenching, infrared temperature measurement, and automated production lines for non-rotating heads and couplings. Innovations such as external thread rolling, variable diameter elbows, friction welding, shot peening, and surface hardening have greatly improved both the quality and performance of today’s sucker rods.
To meet the demands of various challenging well conditions—such as large pumps, deep pumping, heavy oil, high wax, corrosive, and inclined wells—specialized sucker rods have been developed globally. These include ultra-high-strength rods, FRP (Fiber-Reinforced Polymer) rods, hollow rods, KD-grade rods, continuous rods, electrically heated rods, wire rope rods, and aluminum alloy rods. Alongside these, many accessories have been introduced to enhance the performance and longevity of the sucker rod system, such as high-strength polished rods, toothless clamps, rotary devices, shock absorbers, graphite-sealed boxes, roller couplings, centralizers, wax scrapers, weighted rods, anti-fall devices, and magnetic wax prevention systems.
**Technical Principle**
The core of the system is the high-strength sucker rod coupling, which offers excellent tensile strength. The coupling size is typically 5/8", matching or exceeding the performance of the rod itself. To prevent electrochemical corrosion, a sacrificial anode is used, providing cathodic protection through a continuous flow of current. This method protects the rod by sacrificing the anode material, which dissolves gradually in the well fluid. To avoid damage from fluid flow or mechanical impact, stainless steel sheaths are installed around the anode and the rod connections. The coupling is made from high-nickel alloy, ensuring a smooth surface and significantly extending the service life of the coupling.
**Technical Parameters**
- Size: 1", 7/8", 3/4", 5/8"
- Supporting rod diameter: 25mm, 22mm, 19mm, 16mm
- Centralizer outer diameter: up to φ56mm
- Sacrificial anode protection range: 50m
- Effective power generation: ≥1.1 A.h/g
- Anode consumption rate: ≤12.36 kg/A.a
- Current efficiency: ≥65%
**On-site Installation**
During installation, the sucker rod should be connected using threaded joints. The placement of the anti-corrosion and anti-wear device should be based on the specific corrosion and wear conditions of the well, with one section typically installed every 80–100 meters. For optimal performance, this device works best when used in conjunction with the KXY-2 tubing cathodic protector and a standard nylon centralizer.
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Dongguan Shangen Precision Metal Plate Co., Ltd. , https://www.shangenmetal.com