CS seamless pipe is a kind of long steel. The steel pipe has a hollow section and is widely used as a pipeline for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and certain solid materials. Compared with solid steel such as round steel, steel pipe has the same flexural and torsional strength, and is lighter in weight. It is an economical section steel and is widely used in the manufacture of structural parts and mechanical parts, such as oil drill pipes, automobile transmission shafts, bicycle racks and steel scaffolding used in building construction, etc.
Heat treatment of metal materials is divided into overall heat treatment, surface heat treatment and chemical heat treatment. Seamless steel pipe heat treatment generally adopts overall heat treatment. Generally, it goes through basic processes such as heating, insulation and cooling, and defects may occur in these processes. The heat treatment defects of seamless steel pipes mainly include unqualified organizational functions of American standard seamless steel pipes, oversized, surface cracks, abrasions, severe oxidation, decarburization, overheating, overburning, etc.
Common defects of cs seamless pipe
1) Dangerous defects: cracks, inward folds, outward folds, rolling, delamination, scarring, concave pulls, convex hulls, etc.
2) General defects: pits, blue lines, scratches, bumps, slight inner and outer straights, roll marks, etc.
What are most manufacturing defects in seamless steel pipe?
1. Bending of seamless steel pipes
It is a linear or spiral, continuous or discontinuous state existing on the outer or inner surface of seamless steel pipes. The main reasons for folding are poor quality of pipes, folding itself, or inclusions, severe scratches and cracks on the surface, edges and corners at the grinding, and folding after drawing. To avoid folding, the quality of pipes should be improved, and attention should be paid to inspection and grinding.
2. Cracking of seamless steel pipes
It refers to the fine cracks on the inner and outer surfaces of seamless steel pipes that are distributed in a straight line or spiral shape, with a depth of more than 1mm, and are continuous and discontinuous. According to Henggang Manufacturing Co., Ltd., the reasons are: there are subcutaneous bubbles and subcutaneous inclusions in the hot-rolled tube blanks, and there are cracks or deep pits on the steel pipes before drawing. During the hot rolling or cold drawing process, longitudinal scratches or scratches occur during the operation. Preventing the formation of cracks also lies in improving the quality of the tube blanks and strengthening the inspection and grinding of the tubes. At the same time, pitting, scratches and scratches should be avoided during the cold drawing production process.
3. Seamless steel pipe - scratches
The characteristic of this defect is that there are longitudinal linear scratches of varying lengths on the inner and outer surfaces of the seamless pipe. Most of them are groove-shaped, but they may also be raised stripes. The main reasons for scratches (cuts) are: there are scratches inside the pipe, which cannot be eliminated during drawing, the iron oxide film remains on the steel pipe, the mold sticks to the steel, and the strength and hardness of the pipe mold are insufficient or uneven. There is fragmentation and wear, the hammer head is defective, and the sharp edges and corners of the transition part of the hammer head damage the mold. To prevent scratches and scratches, the quality of each preparation process before wire drawing should be improved, and a mold with high strength and hardness and good finish should be selected.
4. Seamless steel pipe pits
This is one of the most common surface defects of seamless pipes. There are local depressions of different areas distributed on the surface of the steel pipe. Some of them are periodic and some are irregular. The pits are caused by the iron oxide scale or other hard dirt pressed into the surface of the steel pipe during drawing or straightening, or the original peeling and peeling of the steel pipe surface. Shandong Huangma Pipe Industry pointed out that the measures to prevent pits are to carefully check the pipe, remove defects such as warping, keep the workplace, tools and lubricants clean, and prevent scale and dirt from falling on the surface of the steel pipe. Pipeline.
When there are smooth or sharp spiral marks on the outer surface of the seamless steel pipe, the straightening machine should be checked. Due to the incorrect position and angle of the straightening roller, the steel pipe rubbed against the shoulder of the edge of the straightening roller during the straightening process. There are worn grooves on the straightening roller, and the ends of the steel pipe may appear on the outer surface of the steel pipe. Pit.
5. Seamless steel pipe pitting surface
Its characteristic is that small pits in the form of flakes and dots appear on the surface of the steel pipe. The main reason for surface pitting is pitting during pickling. After annealing, the oxide scale is too thick and straightened and pressed into the surface of the steel pipe, forming a pitted surface; the steel pipe is stored in a humid environment, and even pitting rust will occur after water ingress. The pitted surface is formed after the rust spots are removed.
6. Seamless steel pipe - spot
Since the seamless steel pipe is in contact with water (or water vapor) during processing or storage, and is not treated in time (such as drying), the traces left by water evaporation are called water spots, such as long-term contact with water or corrosive water. Rust spots are formed when the material is water spots. Water spots generally have no depth, and rust spots often corrode the surface of the steel pipe, and there will still be pitted surfaces after removal.
7. Seamless steel pipe warping
Its characteristics are that the inner and outer surfaces of the seamless steel pipe are partially separated from the metal matrix, and the single piece is blocky, discontinuous, rooted or unrooted on the tube wall, but it cannot be peeled off naturally. The reason is that the steel is of poor quality, there are subcutaneous bubbles, which are exposed after cold drawing; the warping caused by hot rolling is not removed on the cold-drawn tube blank; the original deep and angular horizontal pits on the steel pipe form warping after drawing.
8. Seamless steel pipe - scar
The inner and outer surfaces of the steel pipe are not removed in time due to defects such as folding and warping. In the subsequent processing, thin sheets that cannot be separated from the metal substrate are formed. Some are blocky and discontinuous, rooted or not rooted on the tube wall, but cannot be peeled off naturally. , called scars. Surface defects must be checked and removed in time to eliminate scars.
CS seamless pipe quality inspection method
1.Chemical composition analysis: chemical analysis method, instrumental analysis method (infrared C-S instrument, direct reading spectrometer, zcP, etc.).
1) Infrared C-S instrument: analyze ferroalloys, steelmaking raw materials, C and S elements in steel.
2) Direct reading spectrometer: C, Si, Mn, P, S, Cr, Mo, Ni, Cn, A1, W, V, Ti, B, Nb, As, Sn, Sb, Pb, Bi
3) N-0 instrument: gas content analysis N, O
N-0 instrument: gas content analysis N, O
2.CS seamless pipe sizes and shape inspection
1) Steel pipe wall thickness inspection: micrometer, ultrasonic thickness gauge, no less than 8 points at both ends and record.
2) Check the outer diameter and ovality of the steel pipe: caliper, vernier caliper, ring gauge, and measure the maximum and minimum points.
3) Steel pipe length inspection: steel tape measure, manual, automatic length measurement.
4) Steel tube bending inspection: straightedge, level (1m), feeler gauge, thin wire to measure the bending degree of each meter and the bending degree of the whole length.
5) Inspection of the bevel angle and blunt edge of the steel pipe end face: square ruler, card board.
Summarize
Although seamless steel pipes are known for their high strength and reliability in industrial applications, various defects in production may still affect their performance. Surface defects, continuity defects, internal defects, corrosion and material defects are the five most common problems. These defects will not only reduce the service life of the steel pipe, but may also pose safety risks. Therefore, when producing and using seamless steel pipes, strict quality control measures must be taken to regularly detect and repair defects to ensure that steel pipes can operate safely in various extreme environments.
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