Can carbon steel pipes that have been in use for 20 years be repaired?
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Carbon steel ammonia pipes that have been in use for 20 years require some valves to be removed and some welds to be rewelded； Question: Do the properties of carbon steel ammonia pipes that have been in use for 20 years change? What are the risks of welding?
The design life of normal pipelines is 15 years; it’s still an ammonia pipeline, so corrosion has more or less occurred as well
Make a judgment after conducting a comprehensive thickness measurement of the pipeline. Experience is basically of no use.
1. According to SH/T3059, the design life of pipelines is generally 15 years; pipelines that have a life span of 20 years are operating beyond their designated lifespan. To continue using it, a comprehensive inspection is necessary. Such as the chemical composition of the pipe material, its microstructure and mechanical properties, corrosion conditions, and wall thickness reduction. When conducting welding procedure qualification, these factors must be fully considered to develop a reasonable welding plan, thereby reducing risks. Furthermore, for carbon steel pipes, ammonia (liquid ammonia, gaseous ammonia) is a medium that readily causes stress corrosion cracking. After welding, stress-relief heat treatment should be applied to the welded joint; the measured hardness of both the base material and the weld area as well as the heat-affected zone should be less than or equal to HB185. 2. It’s been 20 years in use; it’s time to replace it. Is that little amount of money really a problem?
As per the design requirements, it may no longer need to be used. After passing the inspection, pay attention during the first welding process to whether the welding parameters are correct and whether the weld cracks. Increase the test pressure of the wastewater using the previous method. Use conservatively