Factors affecting the quality of seamless elbows

Factors affecting the quality of seamless elbows

Seamless elbow is a kind of pipe fitting used in pipeline turns. Among all the pipe fittings used in the pipeline system, it accounts for a relatively large proportion, about 80%. However, if the quality of the seamless elbow is poor or not good at all, and the seamless elbow will be affected by the temperature, corrosion, impact, pressure and other factors of the transport medium, then the seamless elbow in the pipeline will The head will be deformed or directly scrapped, which will affect the transportation of the medium in the pipe, cause medium leakage, and cause the entire pipeline transportation process to fail.

1. The temperature in the furnace during production did not reach the specified temperature.

The raw material for making seamless elbows - round tube billet, is fed into the furnace and heated to a temperature of about 1200 degrees Celsius; flange pipe fittings are usually solid solution treated in the temperature range of 1040 to 1120 degrees Celsius (Japanese standard) to process. It can be observed through the observation hole of the annealing furnace. The flange fittings in the annealing area should be in an incandescent state, but not soften and sag.

2. Improper selection of fuel

When putting the billet into the furnace for heating, fuel needs to be put in. The fuel is hydrogen or acetylene, especially hydrogen. Pure hydrogen is usually used as the annealing atmosphere, and the purity of the atmosphere is preferably above 99.99%. If the other part of the atmosphere is an inert gas, the purity may be reduced, making the seamless elbow much more brittle, and damage and leakage problems may occur when encountering conditions such as high pressure and high temperature. It is important to note that the inert gas must not contain excess oxygen or water vapor.

3. The protective air pressure in the furnace is incorrect

In order to prevent small leaks in seamless elbows, the protective gas in the furnace should maintain a certain positive pressure. If it is hydrogen protective gas, it usually needs to exceed 20kBar.

4. The sealing of the stove is not good enough

Bright annealing furnaces should be closed and isolated from the outside air. If hydrogen is used as shielding gas, only one exhaust port is opened (to ignite the vented hydrogen). The inspection method can be applied to the gaps of the annealing furnace joints using soapy water to see if gas is flowing. This is because the places where gas is easily transported are where the annealing furnace enters the pipe and where the pipe is discharged. The seals here are particularly susceptible to wear and tear, so they should be inspected and replaced frequently.