In this paper, the material defects, working environment and stress characteristics of drill string in railway drilling are analyzed in turn, and then the drill pipe is discussed in combination with the above analysis.

Five specific manifestations of drill string wear, and finally put forward some views on reducing drill string wear.

Keywords: drill string wear in railway drilling

Date of receipt: 2007- 10- 10

Drill string wear is a serious problem in railway drilling. drill rod

When the column is worn to a certain extent, it should be replaced with a new one. At present, the diameter of the drill string

It has not reached the level of automatic monitoring with instruments, and most of them are technicians on the spot.

Visually measure the diameter of drill string with vernier caliper. And use specialized technology.

Personnel monitor the diameter of drill pipe, which is usually used to drill deep holes. When drilling holes

The drill string was badly worn, but it was not noticed.

Under normal circumstances, the drill string is easy to break. In a good geotechnical layer, such as

Results The verticality of the borehole is good, and there is no hole shrinkage and reaming, so it is relatively easy to salvage the drill string.

Otherwise, it will waste a lot of time and cause economic losses.

The loss of success is more obvious. The study of drill string wear has become a part of many scientific and technological work.

People attach great importance to it. The external causes and causes of drill string wear in railway drilling are analyzed.

Internal causes and concrete manifestations of wear and tear.

First, the material defects of drill pipe

From the material point of view, the drill pipe is defective. machine shop

When producing drill pipes, there is a heat treatment process. During heating and cooling,

The internal structure of drill pipe will change. Heat treatment usually eliminates coarse particles in drill pipe.

Weaving makes it exquisite in structure and can bear greater stress. But there are always some defects.

The grain structure of drill pipe was observed under high power electron microscope, and it was found that it was composed of many dislocations.

Children and atoms are arranged in a spatial lattice according to certain rules, and the lattice is general.

In a stable equilibrium state. There are usually a few inclusions between grains,

Cavities and other defects, in these grains, even in the elastic range, when the force is not

If it is too large, plastic deformation may occur.

Second, the drill pipe working environment

Rotary drilling is often used in railway drilling, and it is difficult to get core sand and other rock formations.

Impact drilling is also used in the case of fully weathered layer. The drill string runs with the drill pipe.

The main media of column action include drilling fluid and rock and soil layer.

Railway drilling drilling fluid is generally water-based drilling fluid, which is a kind of multiphase instability.

Fixed system, with water as dispersion medium (continuous phase) and clay as dispersed phase (solid phase),

Add some kind of chemical treatment agent or weighting material. Its composition includes water and swelling.

Wet soil, chemical treatment agent (such as carboxymethyl cellulose), gas (dissolved oxygen,

Carbon dioxide gas, hydrogen sulfide gas) and other corrosive media such as Cl-, SO42-,

Ca2+, CO32- and HCO3- etc.

The common cores in railway drilling are soil layer, sandy pebble layer, completely weathered rock layer,

Strongly weathered fractured zone rock stratum, weakly weathered rock stratum, etc. Sandy pebble layer, hard and strongly weathered.

The drill string wear caused by complex strata such as rock stratum is more serious than that caused by other rock strata.

Third, the working stress characteristics of drill string

In the process of work, the motion mode of drill string includes rotation and drilling around.

The rotation of the heart usually exists in deep hole drilling. bit

The stress on the rod is a compound stress, which mainly includes the following sub-items: drilling the drill pipe.

Tensile stress caused by the dead weight of the bar, bending stress caused by transverse stress,

Shear stress caused by torque, axial and transverse stress caused by drill pipe vibration

Force, friction with rock formation and interaction with drilling fluid.

Fourth, the manifestations of drill pipe wear

1. Abrasive wear

Abrasive wear is caused by external hard particles in the friction pair or micro-peaks on the hard surface.

In the process of relative movement of surfaces, the phenomenon of surface scratch and surface material falling off is caused, and drilling is carried out.

The surface characteristics of pole posts are wear, tear, longitudinal tensile marks, local peeling and cracks.

The wear mechanism of abrasive particles is micro-cutting, multiple plastic deformation leading to fracture and micro-fracture.

The drill string is easy to bend under combined stress. After bending,

There is serious friction between the protruding place and the hard rock stratum. Drill string surface

The thickness of quenching treatment is generally 1 mm, and after the quenching layer is worn off, the subsequent polishing is carried out.

The loss rate will accelerate. In deep hole drilling, sometimes the surface of the drill pipe taken out is bright.

Obvious scratches, which are the performance of abrasive wear.

2. Adhesive wear

When the two pairs of surfaces of the friction pair slide relatively, adhesive wear is caused by adhesion.

Transfer material from one surface to another or fall off the surface.

Caused by abrasion. Because the actual contact area between the two pairs of surfaces of the friction pair is very small

Small, the contact point stress is very high, and the dual surface of the friction pair is at this high temperature and high strain.

In the stressed state, the surface of the rod is broken, so that the contact peaks are attached, and then

The adhesion point is cut off when sliding.

The bending of drill pipe causes local friction with rock stratum, and the local contact point is high.

Stress constitutes the condition of adhesive wear.

3. Fatigue and wear

Fatigue wear refers to the rolling or rolling of two pairs of surfaces of a friction pair (page 185).