The primary 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, while 316 stainless steel pipe is generally thought-about extra corrosion resistant than 304, relying on the nature of the corrosive media the corrosion charges of 304 and 316 may very well be related.
Generally, SS 304/304L is assumed to be corrosion-resistant materials. But once we come to Piping Specs with SS 304/304L MOC, alloy sheet its worth is taken as 0.063 inches — similar for SS316/316L . Please clarify.
We have a plant that produces fertilizer. In a single section we mix 40% phosphoric acid and 98% sulfuric acid together in a ratio of 75-80 : 25-20 phosphoric acid:sulfuric acid. After that the mixture is cooled to a temperature of eighty degrees C. What’s one of the best material of building for transfer piping? The existing material, 304 stainless steel pipe, exhibits problems at the welds.
From a materials of construction perspective, this is a difficult mixture to deal with, particularly at 80 levels C and higher. Phosphoric acid is less corrosive than sulfuric acid. Pure phosphoric acid has no oxidizing energy but industrial phosphoric acid incorporates impurities akin to fluorides and chlorides that can considerably increase its corrosivity. The corrosivity of sulfuric acid is dependent upon many factors including temperature, focus, the presence of oxidizing or lowering impurities, velocity effects, steel tube and solids in suspension.
It is usually not clever to select materials of construction for steel sheet sulfuric acid handling equipment based only on revealed corrosion knowledge since corrosion by sulfuric acid is a posh phenomenon. Small variations in impurities, velocity, or concentration can considerably impact the corrosion charge. Halides usually increase corrosion whereas aeration or the presence of oxidizing brokers often increases the corrosion rate of non-ferrous supplies and reduces the corrosion charges of stainless steel pipe alloys. I strongly recommend laboratory corrosion studies be run on your specific stream as part of your materials of construction choice process.
I have a large storage tank of 93% sulfuric acid. I’m having extreme corrosion of the top of the 4-inch carbon steel outlet pipe. If you cherished this short article and you would like to receive much more info with regards to steel tube (https://www.diigo.com/) kindly stop by our web site. I am considering of changing the outlet pipe with Schedule a hundred and twenty carbon steel pipe. Is there any more resistant material, insert, or coating you possibly can recommend 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 said you’re experiencing problems with 304 stainless steel pipe at the welds. If this is the case, you would possibly consider transferring to 304L stainless steel pipe. Low carbon versions of austenitic Stainless steel seamless pipe like 304L are designed to remove problems related to carbide precipitation and chromium depletion at welds. If 304L does not work, try gradually moving as much as a higher alloy. Possible candidate supplies so as of generally rising corrosion resistance are: 316L stainless steel pipe, 20-sort alloys like 20Cb-3, greater chromium Fe-Ni-Mo alloys like Alloy 31, and nickel-base molybdenum-chromium alloys like C-276.
