The main difference between 304 and 316 stainless steel pipe is that 316 comprises 2%-3% molybdenum and 304 has no molybdenum. The “moly” is added to improve the corrosion resistance to chlorides (like sea water). So, whereas 316 stainless steel pipe is generally thought of extra corrosion resistant than 304, depending on the character of the corrosive media the corrosion rates of 304 and 316 might be comparable.
Generally, SS 304/304L is assumed to be corrosion-resistant material. But once we come to Piping Specs with SS 304/304L MOC, its worth is taken as 0.063 inches — identical for SS316/316L . Please explain.
We’ve a plant that produces fertilizer. If you cherished this information and you desire to acquire guidance concerning alloy bar (https://peatix.com/user/9727737) generously pay a visit to the webpage. In one section we mix 40% phosphoric acid and 98% sulfuric acid collectively in a ratio of 75-80 : 25-20 phosphoric acid:sulfuric acid. After that the mixture is cooled to a temperature of 80 levels C. What’s the best materials of building for switch piping? The existing materials, 304 stainless steel pipe, exhibits issues at the welds.
From a materials of construction perspective, that is a tough mixture to deal with, particularly at 80 degrees C and better. Phosphoric acid is much less corrosive than sulfuric acid. Pure phosphoric acid has no oxidizing power but industrial phosphoric acid contains impurities reminiscent of fluorides and chlorides that may significantly increase its corrosivity. The corrosivity of sulfuric acid will depend on many components together with temperature, concentration, the presence of oxidizing or decreasing impurities, velocity results, and solids in suspension.
It is usually not wise to select materials of development for sulfuric acid handling tools based mostly solely on printed corrosion information since corrosion by sulfuric acid is a complex phenomenon. Small differences in impurities, velocity, or concentration can significantly impression the corrosion price. Halides generally improve corrosion whereas aeration or the presence of oxidizing agents usually increases the corrosion charge of non-ferrous supplies and reduces the corrosion rates of stainless steel pipe alloys. I strongly recommend laboratory corrosion studies be run in your specific stream as a part of your materials of construction selection course of.
I have a large storage tank of 93% sulfuric acid. I am having excessive corrosion of the top of the 4-inch carbon steel outlet pipe. I am pondering of replacing the outlet pipe with Schedule one hundred twenty carbon steel pipe. Is there any extra resistant materials, insert, or coating you could advocate for increased life?
Carbon steels are solely acceptable for 93% sulfuric acid when fluid velocity is low (< 3 ft/sec). For 4-inch diameter piping or less with velocities up to 5.9 ft/sec, 316L stainless steel pipe is a good choice. For velocities higher than 5.9 ft/sec, Alloy 20Cb-3 (UNS N08020) has been used successfully. For additional information, consult NACE Recommended Practice RP-0391 "Materials for the Handling and Storage of Commercial Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures."
In your query, you mentioned you’re experiencing issues with 304 stainless steel pipe at the welds. If that is the case, you would possibly consider shifting to 304L stainless steel pipe. Low carbon versions of austenitic Stainless steel seamless pipe like 304L are designed to eradicate problems associated with carbide precipitation and chromium depletion at welds. If 304L does not work, attempt step by step moving as much as a higher alloy. Possible candidate materials so as of usually rising corrosion resistance are: 316L stainless steel pipe, alloy tube 20-kind alloys like 20Cb-3, larger chromium Fe-Ni-Mo alloys like Alloy 31, and nickel-base molybdenum-chromium alloys like C-276.