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.

Anti-corrosion Technology of Spiral Welded Pipe

We all know that the individual quality of spiral welded pipe is relatively large, so it must be stacked outdoors. But it is difficult to avoid being exposed to the sun and rain. So the rust problem has been puzzled the storage time and conditions of spiral welded pipe. Today, we need to carry out a comprehensive solution to the knowledge of anti-corrosion technology of spiral welded pipe.

The toolrust-removal of spiral welded pipe mainly uses steel wire brush and other tools to polish the steel surface, and then cleans and preheats the spiral welded pipe, which can remove loose or turnup mill scale, rust, welding slag and so on. Using manual tool to remove rust can reach Sa 2 level, using power tools can reach Sa 3 level. If there is steady oxide-scale adhering to the steel pipe surface, the effect of toolrust-removal is not ideal, it can not up to the depth of abrasion pattern that required by anti-corrosion construction.

Pickling refers to use solvents, emulsions to clean the surface of the spiral welded pipe (SSAW steel pipe) delivered by low pressure fluid, to achieve removing of oil, grease, dirt, lubricants, and similar organic matter, but it can not remove the rust, mill scale, welding flux, etc. on the surface of spiral welded pipe. So Pickling can only as an auxiliary mean in the anti-corrosion production. Manufacturer general use chemical and electrolytic two methods for pickling treatment, pipeline anti-corrosion technology only adopts chemical pickling, that can remove mill scale, rust, the old coating. And sometimes it can be used as re-treatment after derusting by sandblast. Although Chemical cleaning can make the surface to achieve a certain degree of cleanliness and roughness, but its anchor is shallow, and it is easy to cause stacking environment pollution of spiral pipe welding.

Reasonable using the means to clean the rusty pipe can ensure that spiral welded pipe serves the production for a long time and create more production efficiency.

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.

Features and Uses of Small Caliber Spiral Welded Pipe

Although small caliber spiral welded pipe is small, its function is a lot. So what the features and uses of small diameter spiral welded pipe are?

Features of small-diameter spiral welded pipe:

The production process of spiral welded pipe is simple, but it has high production efficiency. It can use material to form a larger pipe diameter pipe, it can also use the same width of preform body to product pipes with different diameter. However, compared with the same LSAW steel pipe, the length of weld seam is increased by 30% to 100%, and its production rate is low. Therefore, the smaller diameter of the steel pipe mostly use straight welding, large diameter welded pipes mostly use spiral welded pipe.

Uses of small-diameter spiral welded pipe:

Spiral welded pipe is mainly used in tap water engineering, petrochemical industry, chemical industry, power industry, agricultural irrigation, urban construction, and it is one of the 20 key products for the development of China. It is used for liquid delivery: water supply, drainage. It is used for gas transmission: gas, steam, liquefied petroleum gas. It is used for the structure: piling pipe, bridge girder, the pipe for wharf, road, building structure and so on.

Two Ways of High-frequency Welding

Steel pipe has a variety of production processes. High-frequency welding technology is one of them, it usually used by pipe manufacturers to produce ERW steel pipe. Actually, high-frequency welding can be divided into two ways, resistance welding and IWinduction welding.

What is resistance welding?

The resistance welding is carried out by using a pair of copper electrodes to contact on both sides of the welded steel pipe, induction current penetration is good, the two effects of high frequency current are maximized using since the copper electrode directly contact with the steel plate. The welding efficiency of the resistance welding is high and the power consumption is low, so it is widely used in the production of high speed and low precision pipe. And in the production of special thick steel pipe, it is also necessary to use resistance welding.

But there are two shortcomings in resistance welding: first, copper electrode is in touch with steel plate, so it will wear quickly; second, due to the influence of the flatness of the surface of the steel plate and the straightness of the edge, the current stability of resistance welding is poor, the burr inside and outside the weld is higher. So pipe manufacturers generally do not used this way when welding high-precision and thin-walled tube.

What is IWinduction welding?

IWinduction welding is way that using a turn or more turns of the induction coil harness the outside of welded steel pipe. The effect of multi-turn is better than that of single turn, but the fabrication and installation of multi-turn induction coil is more difficult. When the spacing between induction coil and the steel pipe surface is small, the efficiency is higher, but it is easy to cause electro-discharge between the induction coil and the pipe. Generally, it is appropriate that keep the induction coil from the surface of the steel pipe having 5 ~ 8 mm gap. When using IWinduction welding, as the induction ring is not in contact with the steel plate, there is no wear, which ensures the stability of the welding. The quality of welding steel pipe surface is good, and the weld is flat, so in the production of high-precision pipe,such as API and others, it basically uses the form of induction welding.

Characteristics of Spiral Welded Pipe Production

Several days ago, we shared the introduction of spiral welded pipe (also called SSAW steel pipe), now, let us continue to understand characteristics of spiral welded pipe production.

Characteristics of spiral welded pipe production includes:

(1)Manufacturers can use the same width of the strip steel to produce a variety of diameter steel pipe;

(2)The flatness of pipe is good, the size of it is more accurate, the spiral weld inside and outside increases the rigidity of pipe body, so the production process of SSAW steel pipe doesn't need sizing and straightening process after welding;

(3)Easy to achieve mechanization, automation and continuous production;

(4)Compared to other equipments those have similar size, it has a small size, small footprint and investment, and fast construction;

(5)Compared with the same size of the straight seam welded pipe, the weld seam per unit length of tube stock is comparatively long, which makes spiral welded pipe production has lower productivity.

Two Ways of High-frequency Welding

Steel pipe has a variety of production processes. High-frequency welding technology is one of them, it usually used by pipe manufacturers to produce ERW steel pipe. Actually, high-frequency welding can be divided into two ways, resistance welding and IWinduction welding.

What is resistance welding?

The resistance welding is carried out by using a pair of copper electrodes to contact on both sides of the welded steel pipe, induction current penetration is good, the two effects of high frequency current are maximized using since the copper electrode directly contact with the steel plate. The welding efficiency of the resistance welding is high and the power consumption is low, so it is widely used in the production of high speed and low precision pipe. And in the production of special thick steel pipe, it is also necessary to use resistance welding.

But there are two shortcomings in resistance welding: first, copper electrode is in touch with steel plate, so it will wear quickly; second, due to the influence of the flatness of the surface of the steel plate and the straightness of the edge, the current stability of resistance welding is poor, the burr inside and outside the weld is higher. So pipe manufacturers generally do not used this way when welding high-precision and thin-walled tube.

What is IWinduction welding?

IWinduction welding is way that using a turn or more turns of the induction coil harness the outside of welded steel pipe. The effect of multi-turn is better than that of single turn, but the fabrication and installation of multi-turn induction coil is more difficult. When the spacing between induction coil and the steel pipe surface is small, the efficiency is higher, but it is easy to cause electro-discharge between the induction coil and the pipe. Generally, it is appropriate that keep the induction coil from the surface of the steel pipe having 5 ~ 8 mm gap. When using IWinduction welding, as the induction ring is not in contact with the steel plate, there is no wear, which ensures the stability of the welding. The quality of welding steel pipe surface is good, and the weld is flat, so in the production of high-precision pipe,such as API and others, it basically uses the form of induction welding.