Request specification regarding whether it is permissible to weld galvanized instrument air pipes with carbon steel pipes
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I’m currently at a construction site for a project at my company, where the contractor is welding galvanized steel pipes for instrument air with carbon steel pipes. The supervisor and the client insist that these pipes be replaced, arguing that welding destroys the galvanizing layer, and that carbon steel pipes are prone to corrosion, which could affect the purity requirements of the instrument air in the future. In the projects I’ve worked on before, instrument air ducts were always made using galvanized pipes or stainless steel pipes. This is my first time encountering a situation like this, and I would appreciate it if the experts here could advise me on whether it’s feasible to use welded connections between galvanized pipes and carbon steel pipes for instrument air ducts. Please provide the relevant standard numbers and sources so that I can use them as a reference. Thank you in advance
Using stainless steel pipes is the right choice; everything else is not suitable
Friend upstairs, stainless steel pipes are definitely the best choice, but galvanized steel pipes will also work fine; they are cheaper than stainless steel pipes. What I’m looking for right now are the relevant standards to see if it’s specified that galvanized steel pipes can be welded with carbon steel pipes
Code for Design of Compressed Air Stations 9.0.4: The selection of materials for compressed air pipelines shall comply with the following provisions: 1 For compressed air pipelines that do not require drying or purification, carbon steel pipes may be used； 2 For dry and purified compressed air pipelines with a pressure dew point of 10°C or lower, above -20°C, or containing dust particles with a diameter of 40μm or less but greater than 5μm, carbon steel pipes that have been passivated or hot-dip galvanized can be used ； 3 For dry and purified compressed air pipelines with a pressure dew point of less than or equal to -20°C, greater than or equal to -40°C, or with dust particle sizes of less than or equal to 5μm and greater than or equal to 1μm, stainless steel pipes or copper pipes are recommended ； 4 For dry and purified compressed air pipelines with a pressure dew point below -40°C or dust particles smaller than 1 μm, stainless steel or copper pipes should be used. Stainless steel pipes are too expensive; factories generally use galvanized pipes