E-mail: authentic013@steelpipes-fitting.com
WhatsApp: +86 13668807131
E-mail: authentic013@steelpipes-fitting.com
WhatsApp: +86 13668807131
Feb. 09, 2026
1. Copper Sulfate Drop Test: The copper sulfate drop test is the simplest and quickest way to distinguish between ordinary carbon steel elbows and various stainless steel elbows. The concentration of the copper sulfate solution used is 5-10%. Before conducting the drop test, the test area should be thoroughly cleaned to remove grease or other impurities, and a small area should be wiped with a soft cloth. Then, use a dropper to drop the copper sulfate solution into the clean area. Ordinary carbon steel or iron will form a layer of metallic copper on its surface within seconds, while the stainless steel elbow surface will not produce copper precipitation or appear copper-colored.
2. Magnetic Test: The magnetic test is the simplest way to distinguish between annealed austenitic stainless steel elbows and ferritic stainless steel elbows. Austenitic stainless steel elbows are not magnetic themselves, but will develop slight magnetism after high-pressure cold working; pure chromium steel and low-alloy steel are strongly magnetic steels.
3. Nitric Acid Drop Test: A major characteristic of stainless steel elbows is their excellent resistance to corrosion from concentrated and dilute nitric acid. This characteristic makes them easily distinguishable from most other metals or alloys. However, high-carbon 420 and 440 steels only show slight corrosion in the nitric acid point test, while non-ferrous metals corrode immediately upon contact with concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel elbows.
4. Sulfuric Acid Test: The sulfuric acid immersion test for stainless steel elbows can distinguish between 302 and 304 stainless steel and 316 and 317 stainless steel. The cut edges of the sample are ground finely, then cleaned and passivated for half an hour in a 20-30% nitric acid solution (specific gravity 1.42) at 60-66℃. The sulfuric acid test solution concentration is 10%. The sample is heated to 71℃ and immersed in this hot solution. 302 and 304 stainless steel corrodes rapidly and produces a large number of bubbles, turning black within minutes; 316 and 317 stainless steel samples do not corrode or react slowly (no bubbles are produced), and do not change color within 10-15 minutes. If samples with known compositions are tested simultaneously for approximate comparison, the experimental results will be more accurate.
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Latest News
Industry News
Feb. 09, 2026
How do elbow manufacturers identify stainless steel elbows?
1. Copper Sulfate Drop Test: The copper sulfate drop test is the simplest and quickest way to distinguish between ordinary carbon steel elbows and various stainless steel elbows. The concentration of the copper sulfate solution used is 5-10%. Before conducting the drop test, the test area should be thoroughly cleaned to remove grease or other impurities, and a small area should be wiped with a soft cloth. Then, use a dropper to drop the copper sulfate solution into the clean area. Ordinary carbon steel or iron will form a layer of metallic copper on its surface within seconds, while the stainless steel elbow surface will not produce copper precipitation or a
Industry News
Feb. 05, 2026
The difference between stainless steel and carbon steel
The main difference between stainless steel and carbon steel is that, apart from carbon content, it does not contain any other alloying elements. Carbon steel typically lacks corrosion resistance and is less hard than pure iron;
Industry News
Feb. 02, 2026
How to choose the right flange
Flanges are the "connection points" of piping systems. Inferior flanges often lead to leaks and maintenance problems.
Authentic is here to help you find the right pipe fittings and flanges for your specific needs.
FAQ
What certifications do your products have?
Our products comply with international standards such as ASTM, ANSI, JIS, DIN, and GB. We also hold various certifications to assure quality and reliability, including ISO 9001.
How can I get some samples?
If you need, we will offer you samples for free, but new customers are expected to pay express charge.
To which country have you supplied your products?
We have supplied to Thailand, China Taiwan, Vietnam, India, South Africa, Sudan, Peru, USA, Brazil, Trinidad and Tobago, Kuwait, Qatar, Sri Lanka, Pakistan, Romania, France, Spain, Germany, Belgium, Ukraine etc. (Figures here only include our customers in latest 5 years.)
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authentic013@steelpipes-fitting.com
+86 13668807131
Donghe Industrial Zone, Mengcun County, Cangzhou City, Hebei Province
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