The main reasons for leakage in LSAW (submerged arc welding) steel pipes are as follows:

Welding defect

Incomplete weld penetration: During the welding process, improper control of welding current, voltage, or welding speed leads to incomplete fusion at the root of the weld, resulting in incomplete weld penetration defects. This will make the steel pipe prone to stress concentration at the unwelded area under pressure, which may develop into cracks over time and ultimately lead to leakage.

Weld slag inclusion: During the welding process, incomplete cleaning of the groove, peeling of the electrode coating, or poor welding environment can cause slag to mix into the weld metal and form slag inclusions. Slag inclusion can weaken the effective cross-sectional area of the weld, reduce the strength and sealing of the weld, and easily cause leakage.

Weld porosity: During welding, factors such as moisture on the welding rod, oil or rust on the surface of the welded part, and long welding arc can cause porosity in the weld seam. The presence of pores can damage the density of the weld seam, and under pressure, gas may leak from the pores, leading to medium leakage.

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Mechanical damage: During the transportation and installation of steel pipes, they may be subjected to external mechanical forces such as collision and compression, resulting in surface damage such as dents and scratches. These damages will cause local thinning of the steel pipe wall thickness, reduce strength, and make it prone to rupture and leakage at the damaged location during use.

Ground subsidence: If steel pipes are laid on soft soil foundations or in areas with complex geological conditions, uneven ground subsidence can cause uneven stress on the steel pipes. When the stress exceeds the bearing capacity of the steel pipe, it will deform and crack, leading to leakage.

Earthquake action: In earthquake prone areas, the seismic waves generated by earthquakes can cause strong vibrations and impacts on steel pipes. The connection part of the steel pipe may loosen due to vibration, or the steel pipe itself may break due to stress concentration, causing leakage.

Corrosion factors

Internal wall corrosion: When the medium conveyed by the steel pipe is corrosive, such as liquids or gases containing acid, alkali, salt, etc., it will have a corrosive effect on the internal wall of the steel pipe. Long term corrosion will gradually thin the inner wall of the steel pipe until perforation and leakage occur. In addition, if the medium contains moisture and oxygen, oxygen corrosion can also occur, accelerating the damage to the inner wall of the steel pipe.

External wall corrosion: When steel pipes are buried underground, moisture, electrolytes, microorganisms, etc. in the soil can corrode the external wall of the steel pipe. If there are problems such as damage and aging of the external anti-corrosion layer of the steel pipe, it will directly expose the outer wall of the steel pipe to the corrosive environment, accelerate the corrosion process, and lead to leakage.

Material quality issues

Unqualified chemical composition: During the production process of steel pipes, if the chemical composition of the raw materials does not meet the standard requirements, it will affect the performance of the steel pipes. For example, excessive carbon content can reduce the toughness of steel pipes and make them prone to cracking; Excessive impurities such as sulfur and phosphorus can reduce the corrosion resistance and welding performance of steel pipes, increasing the risk of leakage.

Uneven organization: Improper process control during rolling or heat treatment of steel pipes can lead to uneven internal organization, including defects such as segregation and banded structure. These defects can cause inconsistent mechanical properties of steel pipes, making them prone to damage at weak tissue points under stress, which can lead to leakage.

Unreasonable design and construction

Inaccurate design parameters: When designing a steel pipe pipeline system, if the calculation of parameters such as working pressure, temperature, and flow rate of the pipeline is inaccurate, and the selected steel pipe specifications and wall thickness do not meet the actual usage requirements, it will cause the steel pipe to bear excessive pressure or stress during operation, leading to leakage.

Construction quality issues: During the installation of steel pipes, if the pipe connections are not firm, the sealing is not tight, or if welding is not carried out in accordance with the specifications, it can lead to leakage of the steel pipes during use. In addition, if the pressure testing, blowing and other construction processes of the pipeline system are not strictly carried out according to the standards, there may still be leakage hazards.

The following corresponding measures can be taken to address the different causes of leakage in LSAW Steel Pipes:

Welding defect

Repair welds: For smaller welding defects such as porosity, slag inclusion, etc., grinding can be used to remove the defects, and then repair welding can be carried out. Strictly control the welding process parameters during repair welding to ensure welding quality. For more serious welding defects, such as incomplete penetration, cracks, etc., it is necessary to thoroughly remove the defective area and perform welding again. After welding is completed, non-destructive testing such as radiographic testing, ultrasonic testing, etc. should be carried out to ensure that the weld quality meets the requirements.

Strengthen welding quality control: During the welding process, it is necessary to strictly follow the welding process specifications and control parameters such as welding current, voltage, and welding speed. Strengthen the management of welding materials to ensure that welding rods, wires, etc. meet quality requirements. At the same time, training and assessment should be provided to welders to improve their skill level and quality awareness.

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Repair mechanical damage: For mechanical damage such as pits and scratches on the surface of steel pipes, treatment can be carried out according to the degree of damage. If the damage is minor, polishing can be used to smooth the damaged area and eliminate stress concentration; If the damage is severe and causes the wall thickness of the steel pipe to decrease beyond the specified range, the damaged steel pipe section needs to be replaced.

Dealing with ground subsidence: For steel pipe leaks caused by ground subsidence, it is necessary to reinforce the foundation. Grouting, compaction and other methods can be used to improve the bearing capacity of the foundation and reduce ground settlement. At the same time, repair or replace the deformed steel pipes. During the repair or replacement process, measures should be taken to adjust the stress state of the steel pipes to avoid similar problems from happening again.

Seismic reinforcement: In earthquake prone areas, seismic reinforcement is carried out on steel pipe systems. The seismic resistance of steel pipes can be improved by adding fixed brackets, installing seismic support hangers, and other methods. At the same time, strengthen the connection parts of the steel pipes, such as using flexible connection methods, to meet the deformation requirements during earthquakes.

Corrosion factors

Inner wall anti-corrosion treatment: Select appropriate anti-corrosion measures based on the corrosiveness of the conveying medium. For general corrosive media, the method of coating anti-corrosion coatings can be used for protection; For highly corrosive media, steel pipes lined with corrosion-resistant materials can be used. At the same time, it is necessary to treat the conveying medium, such as removing moisture, oxygen, impurities, etc., to reduce the corrosiveness of the medium. Regularly inspect the inner wall of steel pipes, using equipment such as endoscopes and ultrasonic thickness gauges, to promptly detect corrosion and take corresponding measures.

External anti-corrosion repair: For the corrosion of the outer wall of steel pipes, the first step is to clean the corroded area and remove impurities such as rust and oil stains. Then, different repair methods are adopted according to the degree of corrosion. For minor corrosion, the method of applying anti-corrosion paint can be used for repair; For areas with severe corrosion, methods such as pasting anti-corrosion tape and wrapping fiberglass can be used for repair. At the same time, it is necessary to strengthen the maintenance of the external anti-corrosion layer of steel pipes, regularly check the integrity of the anti-corrosion layer, and promptly repair damaged areas.

Material quality issues

Replace non-conforming materials: If any quality problems are found with the steel pipe material, such as unqualified chemical composition, uneven structure, etc., the batch of steel pipes should be immediately stopped and replaced with steel pipes that meet the quality requirements. At the same time, it is necessary to investigate and handle the suppliers of steel pipes, and require them to bear corresponding responsibilities.

Strengthen material inspection: In the process of steel pipe procurement, it is necessary to strengthen the inspection of materials. Require suppliers to provide quality certification documents and conduct sampling inspections on steel pipes, including chemical composition analysis, mechanical property testing, metallographic structure inspection, etc. Ensure that the purchased steel pipes meet the design and standard requirements, and prevent leakage caused by material quality issues from the source.

Unreasonable design and construction

Optimization design: Evaluate and optimize the original design, recalculate the working pressure, temperature, flow rate and other parameters of the pipeline based on actual usage, and select appropriate steel pipe specifications and wall thickness. At the same time, it is necessary to consider the stress distribution and thermal compensation of the pipeline to ensure the safe and reliable operation of the pipeline system.

Improve construction quality: Strengthen the quality control of the construction process, strictly follow the construction specifications and design requirements for operation. When connecting pipelines, ensure that the connection is firm and well sealed; When welding, welding should be carried out according to the welding process requirements, and the quality of the weld seam should be inspected. After the installation of the pipeline system is completed, strict pressure testing, blowing and other tests should be carried out to ensure that the pipeline system is leak free and unobstructed. Provide training and briefing to construction personnel to enhance their quality awareness and skill level.