The primary distinction between 304 and 316 stainless steel pipe is that 316 accommodates 2%-3% molybdenum and 304 has no molybdenum. The “moly” is added to enhance the corrosion resistance to chlorides (like sea water). So, while 316 stainless steel pipe is usually thought-about more corrosion resistant than 304, depending on the character of the corrosive media the corrosion charges of 304 and 316 might be comparable.
Generally, SS 304/304L is assumed to be corrosion-resistant materials. But once we come to Piping Specs with SS 304/304L MOC, its value is taken as 0.063 inches — identical for SS316/316L . Please explain.
Now we have a plant that produces fertilizer. In one section we mix 40% phosphoric acid and 98% sulfuric acid collectively in a ratio of 75-eighty : 25-20 phosphoric acid:sulfuric acid. After that the mixture is cooled to a temperature of 80 levels C. What’s the perfect material of building for steel tube switch piping? The present materials, 304 stainless steel pipe, exhibits problems at the welds.
From a supplies of development perspective, that is a difficult mixture to deal with, particularly at 80 degrees C and better. Phosphoric acid is less corrosive than sulfuric acid. Pure phosphoric acid has no oxidizing power but industrial phosphoric acid comprises impurities resembling fluorides and chlorides that can significantly enhance its corrosivity. The corrosivity of sulfuric acid depends upon many components including temperature, concentration, the presence of oxidizing or lowering impurities, velocity effects, and solids in suspension.
It’s usually not sensible to pick out materials of development for sulfuric acid dealing with gear primarily based solely on revealed corrosion information since corrosion by sulfuric acid is a posh phenomenon. Small differences in impurities, velocity, or concentration can considerably influence the corrosion price. Halides usually enhance corrosion whereas aeration or the presence of oxidizing agents normally will increase the corrosion rate of non-ferrous supplies and reduces the corrosion rates of stainless steel pipe alloys. I strongly recommend laboratory corrosion studies be run on your particular stream as part of your materials of construction selection process.
I’ve a big storage tank of 93% sulfuric acid. I’m having excessive corrosion of the top of the 4-inch carbon steel outlet pipe. I am pondering of changing the outlet pipe with Schedule one hundred twenty carbon steel pipe. Is there any extra resistant material, insert, or coating you would advocate for elevated 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 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 issues with 304 stainless mold steel pipe on the welds. If you liked this information and you would certainly such as to receive more information pertaining to mechanical steel (www.redsea.gov.eg) kindly visit the web site. If this is the case, you may consider shifting to 304L stainless steel pipe. Low carbon variations of austenitic Stainless steel seamless pipe like 304L are designed to remove problems associated with carbide precipitation and chromium depletion at welds. If 304L does not work, attempt progressively moving as much as the next alloy. Possible candidate supplies so as of usually increasing corrosion resistance are: 316L stainless steel pipe, 20-kind alloys like 20Cb-3, higher chromium Fe-Ni-Mo alloys like Alloy 31, and nickel-base molybdenum-chromium alloys like C-276.