What’s The Difference Between 304 And 316 Stainless Steel Pipe

ROD JACKING & DeFusco Industrial Supply

The main difference between 304 and 316 stainless steel pipe is that 316 contains 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 usually thought-about more corrosion resistant than 304, depending on the nature of the corrosive media the corrosion rates of 304 and 316 might 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, its worth is taken as 0.063 inches — same for SS316/316L . Please clarify.

We have a plant that produces fertilizer. In one part 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 80 degrees C. What is the perfect materials of development for switch piping? The existing materials, 304 stainless steel pipe, reveals problems at the welds.

From a supplies of construction perspective, that is a difficult mixture to deal with, particularly at 80 levels C and better. Phosphoric acid is less corrosive than sulfuric acid. Pure phosphoric acid has no oxidizing energy however business phosphoric acid contains impurities similar to fluorides and chlorides that can considerably improve its corrosivity. The corrosivity of sulfuric acid is determined by many components together with temperature, concentration, the presence of oxidizing or decreasing impurities, velocity results, and solids in suspension.

It is usually not smart to select supplies of building for sulfuric acid handling tools based only on printed corrosion knowledge since corrosion by sulfuric acid is a posh phenomenon. Small variations in impurities, velocity, or concentration can considerably impression the corrosion price. Halides typically increase corrosion while aeration or the presence of oxidizing agents normally increases the corrosion fee of non-ferrous materials and reduces the corrosion rates of stainless steel pipe alloys. I strongly advocate laboratory corrosion studies be run in your specific stream as part of your material of construction selection process.

I have a big storage tank of 93% sulfuric acid. I’m having extreme 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 would recommend 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 question, you mentioned you’re experiencing issues with 304 stainless steel pipe at the welds. If this is the case, you would possibly consider moving to 304L stainless steel pipe. Low carbon versions of austenitic Stainless steel seamless pipe like 304L are designed to eradicate issues related to carbide precipitation and chromium depletion at welds. For more information regarding steel Tube (https://zenwriting.net) stop by our website. If 304L does not work, attempt step by step shifting as much as a better alloy. Possible candidate materials so as of generally increasing corrosion resistance are: 316L stainless steel pipe, 20-type alloys like 20Cb-3, larger chromium Fe-Ni-Mo alloys like Alloy 31, and nickel-base molybdenum-chromium alloys like C-276.

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