We use cookies to offer a better browsing experience, analyze site traffic, and personalize content. By using this site, you agree to our use of cookies.

Accept
Decline

Pipe Knowledge

Sharing China-Made with Global Customers

flange manufacturer,bs1387 pipe,piling steel pipe

Pipe Knowledge

Sharing China-Made with Global Customers

Causes and prevention measures of pores in spiral steel pipe welds,hfw steel pipe factory,carbon steel line pipe,steel tube distributors
BackYou are in :  Home  >  News  >  Pipe Knowledge

Causes and prevention measures of pores in spiral steel pipe welds

Date:2024-03-08View:100Tags:flange manufacturer,bs1387 pipe,piling steel pipe
Defects that are prone to occur in the welding area of spiral steel pipes include pores, hot cracks, and undercuts.
The pores in the spiral steel pipe weld not only affect the tightness of the pipe weld and cause pipeline leakage, but also become an induction point for corrosion, seriously reducing the strength and toughness of the weld.
The factors that cause pores in welds include: moisture, dirt, oxide scale and iron filings in the flux, welding ingredients and coverage thickness, surface quality of the steel plate and steel plate side plate treatment, welding process and steel pipe forming process, etc.

Flux composition. When welding contains an appropriate amount of CaF2 and SiO2, it will absorb a large amount of H2 and generate HF which is highly stable and insoluble in liquid metal, thereby preventing the formation of hydrogen pores and bubbles. Bubbles mostly occur in the center of the weld bead. The main reason is that hydrogen is still hidden in the weld metal in the form of bubbles. Therefore, the measure to eliminate this defect is to first remove the rust, oil, water and moisture from the welding wire and weld. and other substances, followed by the fact that the flux must be dried well to remove moisture. In addition, increasing the current, reducing the welding speed, and slowing down the solidification rate of the molten metal are also very effective.

The accumulation thickness of flux is generally 25-45mm. The accumulation thickness of flux with large particle size and low density is the maximum value, and vice versa. The accumulation thickness of high current and low welding speed is the maximum value. Otherwise, the minimum value is taken. In addition, summer or air When the humidity is high, the recycled flux should be dried before use. Sulfur cracking (cracking caused by sulfur). Cracks caused by sulfides in the sulfur segregation zone entering the weld metal when welding plates with strong sulfur segregation zones (especially soft boiling steel). The reason is that the sulfur segregation zone contains low melting point iron sulfide and the presence of hydrogen in the steel. Therefore, in order to prevent this situation, it is effective to use semi-killed steel or killed steel with less sulfur segregation zone. Secondly, it is also necessary to clean and dry the weld surface and flux.
Steel plate edge treatment.
Rust and burr removal devices should be installed on the edges of steel plates to reduce the possibility of pores. It is best to install the cleaning device behind the edge milling machine and disc shear. The structure of the device is two active wire wheels with adjustable upper and lower clearances on one side, which press the edge of the board up and down. Inclusion of welding slag. The inclusion of welding slag means that part of the welding slag remains in the weld metal.
Weld morphology.
The forming coefficient of the weld is too small, the shape of the weld is narrow and deep, gas and inclusions are not easy to escape, and pores and slag inclusions are easily formed. Generally, the weld forming coefficient is controlled at 1.3-1.5, with the maximum value for thick-walled spiral steel pipes and the minimum value for thin-walled spiral steel pipes. Poor weld penetration. The metal overlap of the inner and outer welds is not enough, and sometimes the welding is not penetrated. This condition is called insufficient weld penetration.
Reduce the secondary magnetic field.
In order to reduce the impact of magnetic blowback, the connection position of the welding cable on the workpiece should be as far away from the welding terminal as possible to avoid the secondary magnetic field generated by some welding cables on the workpiece. Undercut. Undercut is a V-shaped groove appearing on the edge of the weld along the center line of the weld. Undercut occurs when welding speed, current, voltage and other conditions are inappropriate. Among them, too high welding speed is more likely to cause undercut defects than inappropriate current.
Craftsmanship.
The welding speed should be appropriately reduced or the current should be increased to delay the crystallization speed of the weld pool metal to facilitate gas escape. At the same time, if the strip delivery position is unstable, adjustments should be made in time to avoid frequent fine-tuning of the front or rear axles. The bridge remains shaped, making it difficult for gas to escape.