Carbon Steel Pipe Hardness

​The hardness of carbon steel pipe commonly used Brinell, Rockwell, Vickers hardness of three kinds of indicators to measure.

Brinell hardness

In the steel standard, it is the most widely Brinell hardness, often expressed in the indentation hardness of the material in diameter, both intuitive and convenient. However, for a hard steel or steel thin NA.

Rockwell hardness

Rockwell hardness test tube with Brinell hardness test, as are the indentation test methods. The difference is that it is a measure of the indentation depth. Steel Rockwell hardness test is a very wide application, wherein after the Brinell hardness HB HRC use in steel standard. Rockwell applicable to the determination by the extremely soft to extremely hard metal materials, which make up not Brinell method, compared with Brinell method is simple and can be read directly from the dial hardness machine hardness value. However, because of its small indentation, the Brinell hardness values better method is accurate.

Vickers hardness

The welded steel pipe is also a Vickers hardness test indentation test method for the determination of a thin metal material and a surface layer hardness. It has a Brinell, Rockwell main advantages law, and to overcome their basic shortcomings, but not as convenient method Rockwell, Vickers method is rarely used in the steel standard.

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Carbon Steel Pipe Classification

​Carbon steel pipe is a hollow steel bar, a large number of pipes for transporting fluids such as oil, natural gas, water, gas, steam, etc. In addition, engaged in bending, torsional strength, lighter, so it widely used in the manufacture of mechanical parts and engineering structures. Also used in producing a variety of conventional weapons, the barrel, shells and so on.

Carbon steel pipe classification: carbon steel pipe can be divided into seamless steel pipe and welded steel pipe points two categories. By the cross-sectional shape can be divided into the tube and shaped tubes, round steel is widely used, but there are some square, rectangular, semi-circular, hexagonal, equilateral triangle, octagon shaped steel tubing. For steel to withstand fluid pressure hydraulic test should be carried out to test its ability to withstand and quality, does not leak under pressure requirements, wet or expansion of qualified, some steel but also according to the requirements of the standard or demand side, curling trials, flaring test, flattening test.

Seamless steel pipe is ingot made of perforated or solid through the capillary tube, and then hot rolled, cold-rolled or cold call is made. Seamless steel pipe with a diameter* thickness specifications expressed in millimeters. Seamless steel pipe is divide into hot and cold seamless steel categories. Hot-rolled seamless steel pipes of general, low, medium pressure boiler pipe, high pressure boiler pipe, steel pipe, stainless steel pipe, oil cracking pipe, steel pipes and other steel and other geological. Cold-rolled subject to sub- general seamless steel pipe, low pressure boiler pipe, high pressure boiler pipe, steel pipe, stainless steel pipe, oil cracking pipe, the other steel, but also thin-walled carbon steel, alloy steel thin-walled, walled stainless steel, special steel pipe.

Welded steel pipe with plate or strip is bent after forming, then made by welding. Press the seam into the form of DSAW steel pipe. Divided into general -use pipe, galvanized pipe, blowing pipe, wire casing, metric pipe, roller pipe, deep well pump tube, automotive tube, transformer tube, welded tube, welding shaped tube and spiral welded pipe.

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What is NDT Testing

​NDT testing means without prejudice or affect the detected object performance, not hurt at being provided to detect objects within the organization, the use of material internal structural abnormalities or defects heat, sound, light, electricity, magnetism and other reactions caused by changes to physical or chemical methods as a means of using modern technology and equipment, equipment, the specimen surface and the interior of the structural steel pipe, properties, and defect type state, nature, number, shape, position, size, distribution and change inspection and test methods . Non-destructive testing is an effective tool of industrial development is essential, to a certain extent reflects the level of industrial development of a country, the importance of non-destructive testing has been recognized, the main ray inspection (RT), ultrasonic testing (UT), magnetic particle testing (MT) and liquid penetrant testing (PT) four. There are other NDT methods eddy current testing (ECT), acoustic emission testing (AE), thermal imaging / infrared (TIR), leak testing (LT), the AC field measurement techniques (ACFMT), magnetic flux leakage testing (MFL), far-field test detection (RFT), ultrasonic time of flight diffraction method (TOFD) and the like.

NDT testing is the use of sound material, optical, magnetic and electrical characteristics such as, without prejudice or affect the performance of the detection object premise of the existence of defects or unevenness in the detection of the test object, given defect size, location the nature and quantity of information. Compared with the destructive testing, nondestructive testing has the following characteristics of carbon steel pipe. The first is a non-destructive, because when it is done without compromising detection performance by using a detection object; a second comprehensive, since the detection is non-destructive, so the object can be detected 100% comprehensive testing, if necessary this is destructive detection impossible; the third has a full, destructive detection generally apply only to the raw materials testing, such as mechanical engineering commonly used in tension, compression, bending, etc., are for nondestructive testing manufacturing of raw materials, finished products and for the supplies, unless the service is not ready to let it continue, otherwise it is not destructive detection and non-destructive testing without damaging the object to be detected by the use of performance. Therefore, it is not only the raw materials used to manufacture each intermediate step of the process of welded steel pipe, until the final finished products for the entire testing, but also on the service in the device for testing.

NDT Visual inspection: 1, the weld surface defect inspection. Check the weld surface cracks, incomplete penetration and weld leak welding quality. 2, the state examination. Check the surface cracks, peeling, cable, scratches, dents, bumps, spots, corrosion and other defects. 3, cavity inspection. When certain products (such as worm gear pumps, engines, etc.) work, according to the technical requirements of the project will be remote visual inspection. 4, assembly inspection. When required, and when needed, using the same three-dimensional industrial video endoscope assembly quality inspection; or a step after assembly is complete, check the parts and components assembled position meets the conditions for drawing or technical requirements; the existence of assembly defects. 5, extra material inspection. Check the product within the lumen of the residual dust, foreign objects and other remnants.

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DIN30670 for coating steel pipe

​DIN 30670 refers to polyethylene coatings on steel pipes and fittings –Requirements and testing.

This standard specifies requirements for factory-applied three-layer extruded polyethylene-based coatings, and one- or multi-layered sintered polyethylene-based coatings for the corrosion protection of steel pipes and fittings. The coatings are suitable for the protection of buried or submerged steel pipes at design temperatures of –40 °C up to +80 °C. The present standard specifies requirements for coatings that are applied to longitudinally or welded steel pipe or seamless steel pipes and fittings used for the construction of pipelines for conveying liquids or gases. Applying this standard ensures that the PE coating provides sufficient protection against the mechanical, thermal and chemical loads occurring during operation, transport, storage and installation. DIN EN ISO 21809-1 specifies requirements at international level for three-layer extruded polyethylene- and polypropylene-based coatings for steel pipes for petroleum and natural gas pipeline transportation systems. The following fields of application are not covered by DIN EN ISO 21809-1: ─ all polyethylene-based coatings for steel pipes and fittings used for the conveyance and distribution of water and wastewater, ─ all polyethylene-based coatings for steel pipes and fittings in distribution pipelines for gaseous and liquid media, ─ single- and multi-layer sintered polyethylene-based coatings steel pipe and fittings used for transport pipelines and distribution pipelines The present standard remains valid for the above fields of application. Two-layer polyethylene-based coatings are standardized at European level in DIN EN 10288 which was published in December 2003.

Materials shall be selected at the discretion of the coater because, depending on the installation and coating procedure, various materials can be used to comply with the minimum requirements specified in this standard for the finished coating. Any deviating requirements of the purchaser regarding the materials to be used shall be subject to agreement.The surface shall be prepared by removing rust by means of blast cleaning. Blast cleaning and any necessary subsequent work shall not result in the reduction of the minimum wall thickness specified in the technical delivery standards for the steel pipe. Residual abrasive dust shall be removed prior to coating.

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Internal Coated Pipe

Using epoxy powder coating is for 30 years of history in a foreign country due to the wide range of sources of raw materials, production methods are simple, cheap, good performance, which do not pollute the environment and long service life, so far it is a good anti-corrosion coatings. Petroleum Institute of Construction Technology in China for the oil field pipeline corrosion problems and successfully develop the anti-corrosion coating steel pipe of epoxy powder to fill the blank of the domestic pipeline anti-corrosion powder coating. the paint coating has excellent chemical resistance, good mechanical properties, high electrical insulation properties and good toughness. Corrosion tests predict coating life, the conditions intact Chu apply the paint to do the inner coating of oil, gas and water pipes, the life expectancy of up to l5 years; do sewage and mixed water injection pipeline within the coating, life up to 5 to 7 years. The construction method using the pipeline industry, the most widely used static thermal spraying method. According to the data reported, due to the transmission medium, the thickness of the coating of epoxy powder coating requirements are also different. Domestic oil, gas, water and sewage, etc. containing certain corrosive media, anti-corrosion pipe is the best thick coating. Electrostatic heat till coated thick coating, spraying a coating thickness of up to 250 ~ 350/an maximum thickness of up to 500, ~ 'n. Electrostatic Powder the moraine coated is a surface treatment of the solid powder, it has a simple, easy to operate equipment, process, free from the workpiece size limit.

Inner surface heat-resistant paints and coatings

The technology is the surface heat-resistant paint coating that mixed epoxy resin main agent and epoxy resin curing agent in the carbon steel pipe (each about 5.5m), natural drying a certain period of time, more than 6O ℃ warm water or 60 ℃ or more hot air into the tube, forced drying, more than three hours to complete the steel pipe coating. The technology is mainly applied to water pipelines and transmission and hot water pipe internal coated first surface treatment on the pipe wall, and then use the compressor by the pressure of air or nitrogen, Pressure between the resistance and the two applicator thermal coating in the pipe wall to form a uniform coating. Coating must 6O ° C more than warm water or 60 "C, hot air above the mandatory drying and natural drying is heat resistant to dissolution performance decreased significantly.

Epoxy resin latex cement mortar lining

Epoxy resin latex cement mortar lining in the steel tube surface first coated with epoxy cement water-based paint, to form the undercoat, and then based on this coating steel pipe . The use of materials is containing epoxy resin latex cement mortar. Colloidal silicon dioxide is added in the cement mortar. Cement water-based coatings and cement mortar contain ionic latex (a hydrocarbon solvent containing 5 to 8 sugars). The lining of steel pipes, except for sewage and water pipelines is also apply to oil, gas and steam pipelines. In order to get a solid lining, pipe lining before, the surface must be shot peening, shot peening is divided into dry and wet shot peening, if both methods are not adopted, can also be used to pickling.

Pipe Welding Procedure

Under the welded steel pipe from the top of the arc, from top to bottom all-position welding technique, the method of welding speed, weld appearance, good welding quality, you can save welding materials, reduce labor intensity, which is a common SMAW can not be compared and now more widely used in large-caliber long-distance pipeline welding in all position of power in the construction of low-welded large diameter thin-walled tube has some promotional value. 

Under the welding usually select the appropriate welding current, electrode angle and welding speed, straight through drag down or suppress arcing swing slightly to finish welding. Ordinary electrode prone drip drip molten iron and slag under question, and the use of the pipeline dedicated to welding electrodes, welding specifications strictly enforced, you can solve these problems. Cellulose type electrode welding slag less, arc force, stiffness enough to prevent the molten slag and drip down and penetrating arc large, especially for thick-walled containers and welded steel pipe hit the bottom, you can eliminating the root shovel operation, thereby improving work efficiency, improve working conditions, but because of its high hydrogen content of the weld, so for domestic high-pressure structural steel pipe welding current commonly used cellulose electrode backing plus low hydrogen electrodes and filler cap surface welding. 

The right set of tubes and tack welding is on ensuring the quality of the welding, the back of a good weld is an important factor. Tack welding seam is part of a formal, not only requires forming side welding, but also to ensure the welding quality. Tack welding length 20mm, a thickness of about 3mm, gentle slopes on both sides of the weld should be ground into shape, in order to facilitate joint. 

Next to the welding electrode is very important to use the correct angle. Backing weld, filling and capping rod angle is basically the same, but the arc length and transport of a different form. Next to the weld, the weld is controlled by the length and width of the main forms of transportation of the arc, arc and arc close attention to the wrong location should open.

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Mild Steel Pipe

Mild steel pipe refers to the content of less than 0.25% carbon steel because of its low strength, low hardness and soft. It includes most of the part of ordinary carbon steel and high-quality carbon structural steel, mostly without heat treatment used in engineering structures, some carburizing heat treatment and other mechanical parts required for wear. Mild steel pipe annealing organization ferrite and pearlite is lower its strength and hardness, ductility and toughness. Therefore, the cold formability is good and can be crimping, bending, punching and other methods of cold forming. Like that mild steel pipe has good weldability. Carbon content from 0.10 to 0.30% of mild steel is easy to accept all kinds of processing such as forging, welding and cutting, commonly used in the manufacture of chains, rivets, bolts, shafts, etc. 

Ordinary mild steel pipe is for the production of building components, containers, tank, furnace and farm machinery. Quality mild steel pipe is for making car cab, hood and other deep-red products; also rolled into bars, strength requirements for the production of mechanical parts. Before using mild steel pipe is generally not by heat treatment, the carbon content of more than 0.15% by carburizing or cyanide treatment, used to require high surface temperature, wear good shafts, bushings, sprockets and other parts. Due to the low strength of the low-carbon steel, use is restricted. Appropriate to increase the carbon content of manganese and add trace vanadium, titanium, niobium and other alloying elements, can greatly improve the strength of steel. If you reduce the carbon content of the steel and add a small amount of aluminum, and a small amount of boron carbide forming elements, you can get ULCB set high enough intensity, and maintain good ductility and toughness.

Low carbon content of mild steel pipe is very low hardness and poor machinability, normalizing process may improve machinability. Mild steel pipe tends to have a greater timeliness, both quench aging tendencies, as well as a tendency to strain aging. When the rapid cooling from a high temperature steel, ferritic scraping carbon, nitrogen saturation, it can also slow the formation of iron carbonitride was at room temperature, and thus the strength and hardness of steel, the lower the ductility and toughness, a phenomenon called quench aging. Even without quenching and low carbon air cooling will produce aging. Produce large amounts of low-carbon steel by deformation dislocations ferrite from carbon, nitrogen atom elastic dislocation interactions, carbon, nitrogen atom reign gathered around the wrong line. Such a combination of carbon and nitrogen atoms and the dislocation line is called the Coriolis-year-old air mass (Ke lop air mass). It will increase the strength and hardness of steel while reducing ductility and toughness, a phenomenon known as strain aging. Than quench aging of carbon steel pipe during deformation plasticity and toughness greater dangers in the tensile curve has obvious upper and lower yield point. Since the yield on the yield point elongation occurs until the end, appear deformed due to uneven surface with folds formed on the surface of the sample, called Luders band. So many stampings are often scrapped. There are two methods of its prevention. A high pre-deformation method, the pre-deformed steel stamping place after a period of time will produce Luders band, so the pre-deformed steel stamping is placed before the time not too long. Another steel, aluminum or titanium is added to the formation of a stable compound with the nitrogen to prevent the formation of air masses caused by the Coriolis deformation of aging. 

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