Why should composite pipes be left for half an hour before electric fusion welding? Temperature adaptation and welding quality

Why should composite pipes be left for half an hour before electric fusion welding? Direct answer: When transporting pipes between storage and construction sites, if there is a large temperature difference between the two, the surface of the pipe will condense or overheat, carrying condensed water or temperature stress, and directly welded. Water vapor will vaporize at high temperatures, forming pores and greatly reducing the strength of the weld. The standard practice is to place the pipes and fittings at the construction site for at least half an hour before and after connection, allowing the temperature to approach the ambient temperature and the surface to be dry before welding. This step is most easily saved by rushing the schedule during winter and seasonal changes, and it is precisely at this time that it is the most crucial.

What problems does temperature difference bring

Two consequences. One is condensation water: When the cold pipe enters the warm construction site, water droplets immediately condense on the surface, and the welding surface contains water. During electric melting, the water evaporates and produces pores and virtual welding, which cannot be seen from the appearance. It only leaks after pressure testing or operation. The second is thermal stress: when there is a large difference between the temperature of the pipe and the environment, the cooling shrinkage is uneven, and the weld joint bears additional stress during the cooling process, which becomes a crack source after long-term operation. Half an hour of placement is to align the condition of the pipe with the working conditions, with extremely low cost and saving all hidden dangers.

Complete preparation before welding

Leaving it for half an hour is just one part of the process. There are still a few steps to complete the preparation: scraping - using a special scraper or a specified mesh of corundum sandpaper to remove the oxide layer in the welding area. The scraping range should be about one centimeter wider than the insertion depth, and the thickness should be based on visible changes; Cleaning - Use a designated cleaning agent soaked in a lint free clean cloth to wipe the outer surface of the pipe insertion end and the inner surface of the pipe fitting, removing oil and dirt; Marking - Use a marker pen to mark the insertion depth, ensuring that the end face is vertical and free of burrs. Prepare a solid weld joint, cool it down, and then tap to check for a dense sound.

Key points of welding process

The electric fusion welding machine must use specialized equipment provided by the supplier, with parameters set according to the factory settings of the pipe fittings, and should not be adjusted by oneself. During welding, the pipes and fittings should be securely fixed to prevent displacement or protrusion during insertion. It is strictly prohibited to move or test the pressure in advance after welding - the cooling time should be executed according to the regulations, and the uncooled joint will leave residual stress under stress. Record welding parameters and operators for each weld junction, forming a traceable quality file. When installing underground, it is important to remember the principle of minimizing joints: those that can be fully extended do not need short joints, and those that can be welded less should be welded. Each joint is a potential risk point.

Common Error Comparison

Operating steps

1. Pipes and fittings should be brought in half an hour in advance to adapt to the temperature;
2. Check that the surface is dry and free of condensation, and if there is dew, wipe it dry and let it sit;
3. Scrape the oxide layer and clean the welding area;
4. Mark the insertion depth and remove burrs from the vertical end face;
5. After fixation, perform electric fusion welding and record the parameters;
6. Do not move during the cooling period, and conduct a visual inspection after the expiration.

The quality of the weld seam is not visible - welds with intact appearance may have internal pores. Making every step solid is the fundamental way to ensure that every weld can withstand pressure testing and time testing.

Do we still need to place it in summer without temperature difference?

There is still a temperature difference and humidity difference between the warehouse and the outdoor work area. Placing it for half an hour as a standard action is cost-effective and high in safety.

How to determine if the scraping is in place?

The scraping area reveals a fresh and uniform natural color of the material, and the thickness changes can be visually judged. The range covers the insertion depth and is extended by one centimeter.

Can weld joint leakage be repaired?

It is not recommended to perform pressure repair welding on electric fusion joints. Cut and re weld the joints and analyze the reasons. The reliability of the repaired joints cannot be guaranteed.

This article is organized by Luoyang wohong petrochemical equipment co., ltd. the company provides design, manufacture, installation, commissioning and operation and maintenance services for oil and gas recovery equipment, solvent recovery devices and buried composite pipe networks at gas stations, oil depots and chemical enterprises. if you need scheme configuration or on-site investigation, please contact and exchange.