Question regarding the boundary points for changes in pipeline grade
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As the title suggests, when the pipeline grades before and after the valve change, the pressure may remain the same, but the material may change, or both may change. Let’s assume that it’s only the material that has changed; the grade boundary lies at the valve flange. The valve flange is made of carbon steel, while the corresponding pipe flange is a stainless steel flange. I wonder then what material should be used for the bolts connecting these flanges? It seems that bolts made of either stainless steel or carbon steel will corrode. If stainless steel bolts are used, one end of them comes into contact with the carbon steel flange, and as a result the stainless steel bolts corrode. If carbon steel flanges are used, one end of them comes into contact with stainless steel, and in that case the carbon steel flanges corrode. Some people say that protecting carbon steel bolts from corrosion can prevent the corrosion of stainless steel flanges, but it is said that the effect is actually poor. I’d like to ask everyone: how is this kind of flange, which consists of one piece of carbon steel and one piece of stainless steel, handled in practice?
Who says that using carbon steel bolts for corrosion protection isn’t effective? If complete isolation is necessary, then follow the requirements for installing insulated flanges; remember my reply under the account ‘PipeValve’ that contains this information. In other words, plastic sleeves/patches are used for isolation at the locations of different materials.