First, the following precautions should be taken when welding galvanized steel pipes:
1. Galvanized steel pipes with a diameter greater than 100mm should be connected using flanges or compression fittings.
2. To ensure welding quality, the weld joint should be treated with galvanizing. The galvanized layer should be cleaned with a hand grinder or sandpaper or removed with a gas welding flame.
3. The weld joint between the galvanized steel pipe and the flange should be galvanized a second time.

Second, measures to ensure the welding quality of galvanized steel pipes include:
1. Human factors are a key control point in the welding of gas-fired galvanized steel pipes. Due to a lack of necessary post-weld control measures, it is easy to cut corners and affect quality; at the same time, the special characteristics of welding galvanized steel pipes make it difficult to guarantee welding quality. Therefore, before the project begins, skilled welders holding the corresponding boiler and pressure vessel welding certificates or equivalent qualifications should be selected. Necessary technical training and briefings should be provided, and on-site welders should be assessed and approved according to the boiler and pressure vessel welder examination rules before being permitted to enter the site for welding. Welders should not be arbitrarily replaced to ensure the relative stability of the welding personnel for this pipeline.
2. Control of Welding Materials: Ensure that welding materials purchased are from legitimate channels, with quality assurance certificates and conformity certificates, and meet process requirements; the acceptance and issuance procedures for welding materials must be formal and complete, and the recycling of welding rod ends must be strictly controlled to ensure flow and usage; welding materials must be baked strictly according to the process, and each issuance should not exceed half a day's usage.
3. Welding Machine: The welding machine is the tool used for welding and must ensure reliable performance and meet process requirements; the welding machine must have calibrated ammeters and voltmeters to ensure the correct implementation of the welding process. Welding cables should not be too long; if they are too long, welding parameters must be adjusted. 
4. Welding Process: Strictly implement the special operating methods for galvanized steel pipes. Perform pre-weld beveling inspection according to the welding process, control welding process parameters and operating techniques, and conduct post-weld appearance quality inspection. If necessary, add post-weld non-destructive testing. Control the number of weld layers and the amount of welding material used for each weld pass.
5. Welding Environment Control: Ensure that the temperature, humidity, and wind speed meet the process requirements during welding. Welding is prohibited if these conditions are not met.