Which Material Suits Acid and Alkali Storage
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Which Material Suits Acid and Alkali Storage?
Corrosive duty exposes the weakness of the phrase 'chemical resistant'. Resistance is always resistance to something specific, at a specific concentration and temperature. A lining that laughs at 98 percent sulphuric acid at ambient temperature can be destroyed by the same acid diluted and heated, or by a caustic solution that no one thought to mention because it was only used for cleaning.
Selection starts by naming the chemical, the concentration range, the temperature range and the contaminants - and for glass-fused-to-steel that means answering one question first: is there hydrofluoric acid or hot concentrated caustic in the duty? Those are the two chemistries that attack the silica network of the glass itself.
1. Why Are There Two Enemies of Glass?
Fused glass is a silicate network, and two common industrial chemistries attack silicates directly: hydrofluoric acid, and hot concentrated caustic. Everything else is a question of grade, concentration and temperature.
· Hydrofluoric Acid: HF dissolves silica. Any fluoride-bearing acid stream requires a different lining - typically a suitable polymer - regardless of how well glass performs elsewhere.
· Hot Concentrated Caustic: Strong sodium hydroxide at elevated temperature attacks the glass network. At ambient temperature and moderate concentration, GFS performs well; above roughly 60 degrees Celsius with high concentration, review the duty carefully.
· What GFS Handles Well: Standard grades cover roughly pH 3 to 11; specialised three-coat systems extend the range down towards pH 1 for aggressive acid service.
· Temperature Interacts With Chemistry: Every chemical resistance limit is temperature-dependent, so the worst-case combination - highest concentration at highest temperature - is the one that governs.
2. How Do the Common Materials Compare?
Each material has a domain where it is the best answer and a failure mode that disqualifies it elsewhere. Understanding both is the whole of material selection.
· Glass-Fused-to-Steel: Excellent across a broad acid and alkali band, mechanically strong, abrasion resistant, and usable to large diameters. Excluded by HF and by hot concentrated caustic.
· Stainless Steel 316L: Strong with oxidising acids such as nitric and phosphoric, and hygienic. Vulnerable to chloride pitting and stress corrosion cracking, and unsuitable for hydrochloric acid.
· Fusion Bonded Epoxy: Cost-effective for mild service, typically around pH 4 to 10, with a temperature ceiling well below that of glass.
· Polyethylene and Polypropylene: Outstanding resistance to hydrochloric and hydrofluoric acids and to caustic, with a temperature ceiling typically near 60 degrees Celsius and limited fire performance.
· Carbon Steel: Surprisingly suitable for concentrated sulphuric acid above about 93 percent, where the acid passivates the steel, and for some caustic duties - but only within a narrow, well-defined window.
3. How Do You Select in Practice?
Write the duty as a specification, not as a word. Four variables and two questions resolve almost every case.
· Name the Chemical and Concentration Range: Include cleaning chemicals and upset conditions, not just the normal process stream.
· State the Temperature Envelope: Normal operating, maximum, and the temperature during cleaning or steaming.
· Identify Contaminants: Chlorides, fluorides, solvents and oxidisers change the answer even at low concentration.
· Define the Consequence of Failure: A leak of concentrated acid in a groundwater protection zone justifies a different material and a different containment standard than one in a remote industrial yard.
· Confirm With Test Data: Ask the supplier for chemical resistance data and, where the duty is unusual, for immersion test results on the actual coating grade.
Material | Strong Acids | Strong Alkalis | Temperature Limit | Key Exclusion |
Glass-fused-to-steel | Excellent, pH 3-11; pH 1 on special grades | Good at ambient, review above 60 degrees C | High; well above epoxy and polymers | Hydrofluoric acid, hot concentrated caustic |
Stainless steel 316L | Good for oxidising acids; not hydrochloric | Good for most caustic duties | High | Chloride pitting and stress corrosion cracking |
Fusion bonded epoxy | Limited, roughly pH 4-10 | Limited | Moderate | Strong acids, solvents, high temperature |
Polyethylene / polypropylene | Excellent for HCl and HF | Excellent for caustic | Around 60 degrees C | Fire performance, pressure, and UV exposure |
Carbon steel | Concentrated sulphuric acid above about 93% | Some caustic duties within limits | Ambient to moderate | Dilute acids of any kind |
Engineering Assurance and Project Support
Every tank delivered by Shijiazhuang Zhengzhong Technology Co., Ltd. (Center Enamel) is engineered against AWWA D103-09 and EN 1090 with finite element verification of shell, roof and nozzle loads, fused at 820-930°C under ISO 9001 and ISO 45001 control, holiday tested at 1500 V across one hundred percent of the surface, and assembled with Grade 8.8 bolts and manufacturer-certified sealant. Chemical resistance data for each coating grade is supplied with the quotation, and immersion testing against the actual process liquor can be arranged where the duty is unusual or the consequence of failure is high.
"There is no chemical-resistant tank, only a tank resistant to your chemical. Name the concentration and the temperature or the selection is guesswork."
Frequently Asked Questions (FAQ)
Can glass fused to steel store strong acid?
Yes across a broad band. Standard grades cover roughly pH 3 to 11, and specialised three-coat three-fire systems are used for extreme acid service approaching pH 1. The exception is hydrofluoric acid, which attacks the silica network of the glass itself.
Can glass lined tanks store caustic soda?
Yes at ambient temperature and moderate concentration. Strong caustic at elevated temperature attacks the glass network, so duties above roughly 60 degrees Celsius with high concentration need a specific review and may call for a different material.
Why is hydrofluoric acid a problem for glass?
Hydrofluoric acid dissolves silica, which is the backbone of any glass or enamel coating. It is the one common industrial acid that glass-fused-to-steel cannot handle, and fluoride-bearing streams are normally lined with a suitable polymer instead.
When is stainless steel better than GFS for chemicals?
Where the duty involves hot concentrated caustic, hydrofluoric acid, or where a hygienic polished finish and high temperature rating are needed and chloride levels are low. Stainless steel also wins where very small volumes justify a shop-fabricated vessel.
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