Why is it that spiral welded pipe weld defects are allowed to be repaired, but high frequency welded

Because they're different.

The allowable range of spiral steel pipe standard: SY T5037-2000, nominal outer diameter D<508, plus or minus: 508, plus or minus.

The allowable range of the national standard: GB, nominal outer diameter D<508, minus plus 15% T>508, minus positive.

The main differences between the two are:

1. The national standard and thickness are not the same. Within the allowable range of the thickness difference of the national standard; The allowable range of the lower difference of the part standard is less than 1mm.

2. All national standards are detected by ultrasonic, and the ministry standards are sampled.

SY T5037-2000 Nominal Outer Diameter D<508, plus or minus, > 508, plus or minus nominal OD D<508, minus plus plus 15% t, > 508, minus plus.

Seamed steel pipes are much cheaper than seamless steel pipes, but they cannot withstand pressure. Each has its own purpose. For example, of course, seamless steel pipes should be used for high-pressure boilers, and seamed steel pipes should be used for sewage treatment.

The advantage of seamed pipe is that the price is cheap and the process flow is relatively simple.

The disadvantage is that the maximum use pressure that can be withstood is generally within 20 kg, which is the safest range of use. It is generally used for low-pressure fluids such as water, gas, and compressed air. Because the welded pipe has a weld and the mechanical properties of the weld are poor, its scope of application is limited.

The pressure of the seamed pipe is calculated according to the thickness The same as the seamless pipe is not unbearable The thickness of the seamed pipe (advantage) is more balanced There is a seam pipe (disadvantages) There is a weld bead In the use of the general fluid is no problem If the high pressure SCH80 is above recommended to use the seamless pipe The reason is that there are few people who do the seam pipe sch80 The reason is that the amount can not be broken through and no one dares to use the seam sch80 in the pipe making process is limited by equipment and cost problems, so the thickness is cheaper than the seamless pipe If you want to build a thicker pipe, the height of the pipe is seamless It is okay to use it under SCH40.

**Cheap, but not able to withstand pressure, generally used for tubing.

First, the classification is different.

1. Longitudinal steel pipe: divided into metric welded steel pipes, welded thin-walled pipes, transformer cooling oil pipes 2, seamless steel pipes: seamless pipes are divided into hot-rolled pipes, cold-rolled pipes, cold-drawn pipes, extruded pipes, pipe jacking, etc.

According to the cross-sectional shape, seamless steel pipes are divided into two types: round and special-shaped, and special-shaped pipes have a variety of complex shapes: square, oval, triangular, hexagonal, melon-seed-shaped, star-shaped, and finned tubes.

Second, the concept is different.

1. Longitudinal seam steel pipe: Longitudinal seam steel pipe is a steel pipe with a weld seam that is longitudinally parallel to the steel pipe.

2. Seamless steel pipe: A steel pipe made of a whole piece of metal with no joints on the surface is called a seamless steel pipe.

Third, the use is different.

1. Straight seam steel pipe: Straight seam steel pipe is mainly used in water engineering, petrochemical industry, chemical industry, power industry, agricultural irrigation, and urban construction. For liquid transportation:

Water supply and drainage. For gas transportation: coal gas, steam, liquefied petroleum gas.

For structural purposes: as piling pipes, bridges; Pipes for wharves, roads, building structures, etc.

2. Seamless steel pipe: Seamless steel pipe has a hollow cross-section, which is widely used as a pipeline for transporting fluids, such as pipelines for transporting oil, natural gas, gas, water and some solid materials. Compared with solid steel such as round bar, steel pipe has the same bending and torsional strength, and is lighter in weight, which is an economical cross-section steel.

Hope it helps, dear

There are two types of welded steel pipes: one is straight line welding and the other is spiral welding. Welding methods: high-frequency welding, arc welding, etc. High-frequency welded pipes are generally longitudinally welded, but longitudinal welded steel pipes are not necessarily high-frequency welded.

There is a high-frequency welding process in the longitudinal welded steel pipe, and the longitudinal seam steel pipe is divided into high-frequency welding and double-sided submerged arc welding!

Answer: Hello, there is a significant difference between the welding method of high-frequency welded steel pipe and laser welded pipe. Since the welding is completed instantaneously at high speed, the difficulty of ensuring the welding quality is much higher than that of submerged arc welding.

After the hot-rolled coil is formed by the forming machine, the skin effect and proximity effect of the high-frequency current are used to heat and melt the edge of the tube blank, and the pressure welding is carried out under the action of the extrusion roller to achieve production.

Longitudinal welded pipe, steel pipe made of hot-rolled or cold-rolled steel plate or steel strip coil welded by longitudinal seam welding on welding equipment is called longitudinal welded pipe. (It is named because the weld of the steel pipe is in a straight line).

Relatively good.

High-frequency welded pipes are steel pipes that are automatically welded by high-frequency welding equipment.

Steel pipes are welded finished products.

Strength characteristics.

When the pipe is subjected to internal pressure, there are usually two main stresses on the pipe wall, namely radial stress δy and axial stress δx. The resultant stress at the weld δ=δy(L 4sin2 +cos2 )1 2, where is the helix angle of the spiral welded pipe weld.

The helix angle of the spiral weld is generally 50-75 degrees, so the resultant stress at the spiral weld is 60-85% of the principal stress of the straight welded pipe. Under the same working pressure, the wall thickness of spiral welded pipe with the same diameter can be reduced compared with that of longitudinal welded pipe.

According to the above characteristics, it can be known:

a?When the spiral welded pipe is blasted, because the normal stress and the synthetic stress of the weld are relatively small, the burst generally does not originate from the spiral weld, and its safety is higher than that of the straight welded pipe.

b.When there is a parallel defect near the spiral weld, the risk of propagation is not as great as that of the straight weld because the force on the spiral weld is smaller.

c.Since the radial stress is the maximum stress present on the steel pipe, the weld is subjected to the maximum load when it is in the direction of the vertical stress. That is, the vertical seam bears the maximum load, the circumferential weld bears the least load, and the spiral seam is in between.