Seamless Carbon Steel VS Welded Carbon Steel

Carbon steel pipe is most commonly used in critical engineering applications. It may also be used in automotive applications or structural applications as well. Carbon steel piping is important in applications from oil and gas to control lines or electrical lines. Depending on the job at hand determine

whether you are in need of seamless carbon steel pipe or welded carbon steel pipe.

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Welded carbon steel piping is formed from an originally flat piece of carbon steel. The piece of carbon steel is rolled and welded creating a welded seam going long ways down your piece of carbon steel tubing or piping. The weld is formed by using a high energy source to melt the local metal together. Thus creating a weld bead when squeezed together. You will notices where the welded seam is the weld bead. This will be raised compared to the rest of the carbon steel pipe. You will find that some seams are manipulated to become more flush with the piping, while others are sold “as-weld” meaning they are left how they are welded with no further processing to the carbon steel.

Seamless carbon steel tubing or piping, also referred to as drawn piping starts with a solid bar or block of carbon steel. The piece of carbon steel is then put through a process of drilling, extrusion, or oxygen lance to create a hollow pipe. Once the tubing is hollow it is then placed through a die and mandrel phase to create a larger interior diameter providing various sizes of seamless carbon steel tubing.

Detailed Notes to Welding Inspection of Welded Steel Pipe

The contents of the welded steel pipe welding inspection include the inspection of the materials, tools, equipment used in the whole production process, process and finished product from drawing design to product completed. It is divided into three stages: pre-weld inspection, inspection in welding process, finished product inspection after welding. According to whether damage the welded carbon steel pipe or not, test methods can be divided into destructive testing and non-destructive testing two categories. Next, Prime Steel Pipe will provide all for everyone.

Pre-weld inspection

Pre-weld inspection includes the inspection of raw materials (such as base metal, electrodes, flux, etc.) and the inspection of welding structure design.

Inspection in welding process

Inspection in welding process includes the inspection of welding process specifications, the inspection of weld size, the inspection of fixture conditions and structural assembly quality.

Finished product inspection after welding

There are many methods of finished product inspection after welding, commonly used are the following:

No 1. Appearance inspection

The appearance inspection of the welded joint is a inspection method with simple procedure, but it is widely used, and it is an important part of the finished product inspection. It is mainly used to find the defect on the surface of welded steel pipe weld seam and the size of the deviation. We generally observe through the naked eye, or testing by virtue of the standard model, gauge and magnifying glass and other tools. If there is a defect on the surface of the weld seam, it is possible that there is a defect in the weld.

No 2. Confidentiality testing

The defects of brazing joints of welded seam of welded vessel for the temporarystorage of a gas orliquid, such as perfoliate cracks, porosity, slag inclusion, incomplete fusion and loose organization, etc. can be found by compactness test. Compactness test includes kerosene test, water-bearing test, hose test, etc.

No 3. Strength test of the pressure vessel

Except carrying out encapsulation test, we also should carry out strength test to pressure vessel. Two kinds of methods are commonly, hydraulic pressure test and air pressure test. Each of them can test the welded seam compactness of vessel and pipe working under pressure. Pneumatic tests are more sensitive and rapid than hydrostatic tests, the tested products need not to drain off water,it is particularly suitable for difficult drainage products. But the risk of testing is bigger than the hydraulic test. During the test, the corresponding safety and technical measures must be observed to prevent accidents during the test.

No 4. Physical inspection method

Physical inspection method is a method that using some physical phenomena to measure or test. the inspection of materials or parts of the internal defects, generally use non-destructive testing methods. Currently, non-destructive testing includes ultrasonic testing, ray detection, penetration testing, magnetic detection and so on.

① Ray detection

Ray detection is a detection method that use the characteristics of ray can penetrate the material and has attenuation in the material to find defects. Ray inspection is mainly used to test the cracks inside the weld, incomplete penetration, porosity, slag and other defects.

② Ultrasonic testing

Ultrasound can spread in the metal and other uniform media, due to it will produce reflection in the interface of different media, it can be used for testing internal defects. Ultrasonic can test the defect of any welding material and on any part, and it can be more sensitive to find the location of defects. But the nature of defects, shape and size is more difficult to determine. So ultrasonic testing often used in conjunction with the ray test.

③ Magnaflux inspection

Magnaflux inspection is a detection method that use the leakage of magnetic produced by magnetic field, magnetized iron, magnetic metal parts to find defects. According to different methods of magnetic flux leakage, it can be divided into magnetic powder, magnetic induction and magnetic recording method, magnetic powder is the most widely use method. Magnetic flaw detection can only discover the defect on the surface or the near surface of the magnetic metal.

④ Penetration testing

Permeability testing uses certain liquids such as the permeability of the physical properties to find and display defects, including color inspection and fluorescence detection It can be used to check the defect on the surface of ferromagnetic and non-ferromagnetic material.

Surface Treatment of High-frequency Welded Steel Pipe

long-distance oil/gas pipeline is an important way of energy security, in the oil (gas) pipeline anti-corrosion construction process, the surface treatment of high-frequency welded steel pipe is one of the key factors to determine the useful life of the pipeline. It is the premise that the erosion resistant coating can be firmly bonded to the steel pipe. According to the research institutions, the life of the erosion resistant coating depends on the coating type, coating quality, construction environment and other factors. The surface treatment of steel pipe accounted for about 50% on the life of the erosion resistant coating. therefore, we should be strictly in accordance with the requirements specification of erosion resistant coating to steel pipe surface, continue to explore and summarize, and constantly improve the surface treatment of steel.

1. Cleaning

Using solvents and emulsions to clean the surface of steel to achieve the removal of oil, grease, dust, lubricants and similar things, but it can not remove the rust, oxide, welding, etc. on steel surface, so it only can be an auxiliary means in anti-corrosion production.

2. Toolrust-removal

We mainly use steel wire brush and other tools to polish the steel surface, which can remove loose or tilt oxide, rust, welding slag and so on. Manual tool derusting can reach Sa2 level, power tools derusting can reach Sa3 level. If the steel surface attached to a solid iron oxide skin, the effect of toolrust-removal is not ideal, and can not up to the depth of the anchor required by anti-corrosion construction.

3. Pickling

Generally, we use chemical and electrolytic two methods for pickling treatment. Pipeline corrosion only uses chemical pickling, which can remove the oxide, rust and the old coating. And sometimes it can be used as a re-treatment after derusting by sandblast. Although using chemical to clean the surface can achieve a certain degree of cleanliness and roughness, but the anchor is shallow, and it easy to cause pollution to the environment.

4. Abrasive blasting

Abrasive blasting is through high-power motor rotating to drive jet vane to rotate on high speed to make steel sand, steel balls, wire segments, minerals and other abrasives doing spray treatment on the surface of the steel pipe in the centrifugal force. This method not only can completely remove the rust, oxides and dirt, but the steel pipe under the action of the abrasive impact and friction also can achieve the required uniform roughness.

After the spray treatment, we not only can expand the physical adsorption of the surface of the tube, but also enhance the coating and the pipe surface of the mechanical adhesion. Therefore, the spray (throw) treatment is the ideal way to rust rust pipe repair. In general, shot peening (sand) derusting is mainly used for pipe internal surface treatment, shot blasting (sand) derusting is mainly used for pipe external surface treatment.