The primary distinction 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, while 316 stainless steel pipe is generally considered extra corrosion resistant than 304, depending on the nature 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 after we come to Piping Specs with SS 304/304L MOC, its worth is taken as 0.063 inches — same for stainless steel pipe SS316/316L . Please clarify.
We’ve a plant that produces fertilizer. In a single section we mix 40% phosphoric acid and 98% sulfuric acid together in a ratio of 75-eighty : 25-20 phosphoric acid:sulfuric acid. After that the mixture is cooled to a temperature of eighty degrees C. What is one of the best materials of development for switch piping? The present materials, 304 stainless steel pipe, shows issues on the welds.
From a materials of development perspective, this is a tough mixture to deal with, especially at 80 degrees C and higher. Phosphoric acid is much less corrosive than sulfuric acid. Pure phosphoric acid has no oxidizing energy however business phosphoric acid accommodates impurities equivalent to fluorides and chlorides that can considerably enhance its corrosivity. The corrosivity of sulfuric acid depends upon many components together with temperature, concentration, the presence of oxidizing or reducing impurities, velocity results, and solids in suspension.
It’s often not clever to pick supplies of construction for sulfuric acid handling tools based only on printed corrosion information since corrosion by sulfuric acid is a complex phenomenon. Small variations in impurities, velocity, or focus can considerably influence the corrosion rate. Halides typically increase corrosion while aeration or the presence of oxidizing brokers usually will increase the corrosion price of non-ferrous materials and reduces the corrosion charges of stainless steel pipe alloys. I strongly advocate laboratory corrosion studies be run in your specific stream as a part of your materials of development choice course of.
I’ve a large storage tank of 93% sulfuric acid. I am having extreme corrosion of the top of the 4-inch carbon steel outlet pipe. I’m pondering of replacing the outlet pipe with Schedule a hundred and twenty carbon steel tube pipe. Is there any extra resistant materials, insert, or coating you may suggest for increased life?
Carbon steels are only 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 sheet 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 said you are experiencing problems with 304 stainless steel pipe (http://Huldadarnell20.Wikidot.com/) on the welds. If that is the case, you would possibly consider moving to 304L stainless steel pipe. Low carbon variations 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, try step by step moving up to a better alloy. Possible candidate supplies in order of typically rising corrosion resistance are: steel pipe 316L stainless steel pipe, 20-kind alloys like 20Cb-3, larger chromium Fe-Ni-Mo alloys like Alloy 31, and nickel-base molybdenum-chromium alloys like C-276.