Drill pipe is a steel pipe with threads at the tail end, which is used to connect the
surface equipment of the drilling rig and the drilling and grinding equipment
or bottom hole device at the bottom of the well. It is an OCTG pipe, which
is used to transport drilling mud to the drill bit and raise, lower or rotate
the bottom hole device together with the drill bit.
Drill pipe internal coating is a coating
treatment performed inside the drill pipe. Its main function is to prevent
rust, corrosion, reduce friction, and increase wear resistance. The coating can
not only increase the service life of the drill pipe, but also improve the
exploration efficiency and the success rate of drilling.
The main reasons for the shedding and
corrosion of the drill pipe internal coating include the following aspects:
1. Chloride ion damage in salt water
slurry: When the drill pipe is operating in salt water slurry, chloride ions
will destroy the coating structure and penetrate the coating, catalyze and
accelerate the corrosion of dissolved oxygen on the drill pipe substrate,
resulting in coating shedding and pipe corrosion.
2. Erosion corrosion in high temperature
and high flow rate environment: In a high temperature and high flow rate
multiphase flow environment, the drill pipe internal coating is susceptible to
erosion corrosion. Experiments show that in an environment containing sand or
water-carrying sand, the impedance of the coating in the low-frequency zone is
severely reduced and the coating surface is damaged and ineffective.
3. Ultraviolet aging: Ultraviolet rays play a decisive role in the
aging of the coating. Long-term ultraviolet irradiation can easily lead to
molecular chain breakage, resulting in coating powdering.
4. Reasons for the peeling of mechanical paint surface: Including
factors such as poor polishing process, incomplete curing of the paint film,
erosion by pollutants, and poor bonding between the original paint on the
substrate and the water-based paint.
Prevention and solution measures:
1. Choose suitable coating materials: Choose suitable coating
materials for different working environments. For example, in a salt water
slurry environment, a coating material resistant to chloride ion erosion should
be used.
2. Control environmental factors: In a high
temperature and high flow rate environment, try to avoid an environment
containing sand or water-carrying sand to reduce the impact of erosion
corrosion.
3. Strengthen coating protection: In areas
with strong ultraviolet radiation, take appropriate shading measures to prevent
long-term aging of the coating by ultraviolet rays.
4. Optimize the grinding and curing
process: Ensure that the grinding process is meticulous, the paint film is
completely cured, avoid erosion by pollutants, and enhance the bonding force
between the substrate and the coating.
Summary
The reasons for the rapid corrosion of the
coating on the drill pipe include chloride ion damage, erosion corrosion,
ultraviolet aging, etc. Reasonable prevention and solution measures can
effectively extend the service life of the coating on the drill pipe and reduce
the occurrence of shedding and corrosion.