As someone who’s spent nearly a decade on the production floor and in customer consultations as a sodium hydrosulphide (NaHS) 70% supplier, I’ve lost count of how often I get asked a single question—usually by a plant engineer mid-call, when their equipment is already showing early signs of rust: Does this stuff eat through our pipes, reactors, and storage tanks, or is it manageable? For too long, there’s been a messy mix of fear and half-formed assumptions around NaHS 70% and its impact on corrosion, and I wanted to break down what I’ve learned firsthand, no textbook jargon that’ll make you zone out. Sodium Hydrosulphide 70%
First, let’s ground this in what NaHS 70% actually is, because a lot of the confusion starts here. Most people who don’t work with it daily don’t realize this isn’t the same as the smelly, dilute solution you might encounter in a high school chem lab. Our 70% grade is a solid, flake-like product (technically an anhydrous or near-anhydrous blend—we control moisture content super tightly) that’s dissolved into water for 90% of industrial uses. That concentration is the sweet spot for customers in mining, pulp and paper, oil and gas, and wastewater treatment, because it’s more transportable, has a longer shelf life than lower grades, and cuts down on shipping and storage volume. But here’s the critical part: when it’s dissolved into process water, it doesn’t stay as neat NaHS. It breaks down into hydrogen sulphide (H₂S), sodium ions (Na⁺), and hydroxide ions (OH⁻)—and that’s the mix that interacts with metal surfaces.
Let’s start with the “bad” side, because that’s where the concern lives. A common scenario I walk customers through is a gold leaching plant in Nevada that called us two years ago. They’d been using a competitor’s 60% NaHS grade for three months, and their carbon steel leaching tanks were developing pitting corrosion within 18 months of installation. When we sent a field technician to check, here’s what we found: their process water was slightly acidic (pH 5.8), so when they diluted the competitor’s product, the breakdown of NaHS produced a lot more H₂S gas that didn’t stay dissolved. That H₂S reacted with iron in the steel to form iron sulphide (FeS) deposits, but the problem was the porosity of those deposits. Instead of forming a tight, protective layer over the steel, the FeS flakes left gaps—so the underlying metal was exposed, and the acidic process water plus continued reaction created localized pitting that ate through the tank walls. The competitor’s lower-grade product had more impurities, like free sulphur and small amounts of sodium sulphate, that sped up that breakdown; our 70% grade, with 99% purity, doesn’t have those extra contaminants to throw the reaction off.
Wait, but that’s not the whole story, right? I’ve also seen plants where NaHS 70% was added, and corrosion rates dropped. A pulp mill in the Pacific Northwest switched to our NaHS grade in 2021 for their black liquor recovery process, and their stainless steel evaporators went from 0.2 mm of corrosion per year to 0.06 mm. How? Let’s talk about pH and material compatibility. NaHS is an alkaline product—when dissolved in water, it raises the pH. If the process environment is already slightly alkaline (pH 7.5 to 9, which is common in many industrial processes), the OH⁻ ions from NaHS dissolve react with the surface of carbon steel to form a thin, passive layer of iron hydroxide (Fe(OH)₂) and then magnetite (Fe₃O₄). That layer acts as a barrier, keeping water and other corrosive agents from reaching the metal. It’s not a permanent shield, but it’s enough to slow general corrosion down drastically, not speed it up. The H₂S from NaHS breaks down under alkaline conditions too, forming sulphide ions that react with iron to form FeS—but this time, if the pH is controlled, the FeS layer is dense and adheres to the passive layer, reinforcing it instead of puncturing it.
So why the conflicting results? The biggest mistake customers make is not matching their NaHS grade and handling to their specific process conditions. Let’s break down the three main variables that determine how NaHS 70% affects corrosion, because this is the part I wish more process engineers paid attention to.
First variable: pH of the process stream. This is non-negotiable. If your process is acidic (pH < 7), NaHS will react with the excess H⁺ ions to produce large amounts of dissolved H₂S, which can escape as gas. That’s when you get pitting, as the H₂S reacts with iron to form porous FeS. If your process is alkaline (pH > 8.5), the H₂S stays dissolved as sulphide ions, which form that protective FeS layer. I remember a copper mining operation in Arizona that was operating at pH 6.2 when they first tried NaHS; their corrosion rates spiked. We suggested they adjust their process pH up to 7.8 with a small dose of caustic soda, and switch to our 70% grade (instead of their previous 50% grade that had more free acid impurities). Within six months, their pitting corrosion stopped entirely. They ended up placing a bulk order that’s been renewing every quarter since.
Second variable: material of construction. Not all metals react the same way with NaHS. Carbon steel is tricky, like the Nevada gold plant found—if pH is low, carbon steel corrodes fast, but at high pH, it forms that protective layer. Stainless steel is a different animal. 304 and 316 stainless, the two most common grades in industrial equipment, actually handle NaHS well if there’s not too much H₂S present, but wait—if H₂S levels are very high (over 100 ppm) and the pH is between 4 and 7, stainless steel can suffer from stress corrosion cracking (SCC). That’s a sneaky type of corrosion where small cracks form under the surface, often without visible warning, which is way more dangerous than general pitting. We’ve seen this in oil and gas pipelines that use NaHS for sour gas treating, where H₂S levels are high—they had to switch to alloy 22 or duplex stainless steel to prevent that. On the flip side, copper and brass? They’re highly susceptible to corrosion from NaHS, full stop. If you have copper pipes in your process, NaHS 70% will eat through them rapidly, no matter the pH—we always recommend switching to HDPE or lined steel for lines that carry NaHS, even for short runs.
Third variable: impurities in the NaHS product. This is where our 70% grade stands out, because we test every batch to ensure it’s at least 99% pure, with less than 0.5% total impurities (free sulphur, sodium sulphide, moisture). A lot of lower-grade NaHS (like 50% or 60% products from some manufacturers) have 3-5% impurities, which include elemental sulphur. That free sulphur reacts with NaHS in solution to form polysulphides, which are way more corrosive than regular sulphide ions. The Nevada gold plant’s issue? Their competitor’s product had 2.8% free sulphur, which made their H₂S production way higher and the FeS layer porous. Our 70% grade has less than 0.3% free sulphur, so that reaction doesn’t happen. I once got a call from a chemical processor that had been using a European NaHS grade; their reactor was corroding at 0.5 mm/year. We sent a 100 kg trial of our 70% grade, and they tested it and found their corrosion rate dropped to 0.12 mm/year—all because the impurities were gone.
Now, let’s talk about real-world best practices that I’ve shared with dozens of customers, because this is what prevents corrosion issues, not just theoretical science. First, always test your NaHS batch before full-scale use. A small 500 ml lab test can tell you how your specific process water will react with our 70% grade—measure pH before and after adding NaHS, test for H₂S levels, and do a quick corrosion coupon test with your equipment’s material of construction. Second, control pH within that sweet spot of 7.5 to 9 for most applications. If your process naturally runs acidic, add a small amount of caustic soda along with NaHS to adjust it—this is a small cost that saves tens of thousands in equipment repairs. Third, monitor H₂S levels regularly, especially in enclosed spaces where H₂S gas can build up (it’s toxic, too, so safety is a double win). If H₂S levels are over 100 ppm, you might need to adjust your NaHS feed rate or upgrade your material to a higher alloy. Fourth, store NaHS 70% correctly—keep it in tightly sealed, lined steel drums or tanks, because moisture exposure can cause it to degrade, releasing more H₂S and impurities that accelerate corrosion. We always give customers a free storage guide when they place their first order, because even the best product will cause issues if it’s stored wrong.
I want to be transparent here—NaHS 70% isn’t a corrosion cure-all. It’s a chemical that interacts with metal surfaces, and whether it helps or hurts depends entirely on how you use it. I’ve had customers come to me thinking NaHS is evil, only to adjust their pH and material, and see their corrosion problems vanish. I’ve also had customers who used it wrong for years, and had to replace their entire tank farm because they didn’t understand the variables. That’s why as a supplier, we don’t just sell you a bag or drum of NaHS—we offer free process consultations, send field technicians to check your equipment if you’re having issues, and work with you to tailor the product and handling to your specific operations. We don’t push our 70% grade if it’s not the right fit—if you only need NaHS for a small process that runs at very low pH, we’ll recommend a lower-grade product that works better for you, because we want long-term partnerships, not one-off sales.
If you’re dealing with corrosion related to sodium hydrosulphide 70%, or just want to optimize your process to avoid future issues, we’re here to help. You can reach out to our team to discuss your specific needs, get a custom quote for bulk or small orders, or schedule a free process assessment. Don’t wait until a small rust spot turns into a costly equipment failure—let’s work together to find the right solution for your operations.
Sodium Tripolyphosphate(STPP) References
- Corrosion Costs and Preventive Strategies in the United States, NACE International, 2002
- Sodium Hydrosulfide: Properties, Applications, and Safety, Industrial Chemistry Research Institute, 2019
- Effects of pH and Concentration on Carbon Steel Corrosion in Sodium Hydrosulfide Solutions, Journal of Materials Engineering and Performance, Vol. 28, No. 10, 2019
- Stress Corrosion Cracking in H2S Environments, NACE Standard MR0175/ISO 15156, 2020
Tianjin JOY Co., Ltd.
Tianjin JOY Co., Ltd. is one of the most professional sodium hydrosulphide 70% manufacturers and suppliers in China, specialized in providing high quality sodium sulphide and sodium hydrosulfide. We warmly welcome you to buy sodium hydrosulphide 70% made in China here from our factory.
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