00:00I'm here with two sheets of stainless steel side by side. Looking at them,
00:06can you tell me which one is the genuine stainless steel and which one is the fake?
00:11The appearance is practically identical. The shine is the same, the feel is the same,
00:17but the difference between these two sheets can determine whether your kitchen sink
00:23will last for decades or if you show unexpected rust.
00:30In a short time.
00:35Today we're going to do a practical test to differentiate grade 304 stainless steel
00:41from 200 series steel using a chemical product to show you in practice how to identify if you bought
00:50the right steel. To understand why this test is necessary, we need to understand what makes
00:56stainless steel resistant to corrosion, where the key element is chromium, when steel contains at least
01:0410.5%. The element reacts with the oxygen present in the air and forms an invisible and extremely thin
01:15layer on the surface of the metal called the passive layer. This layer acts as a barrier that prevents
01:23the iron from coming into contact with oxygen and moisture preventing oxidation. It's as if the steel
01:30creates its own invisible armor which regenerates itself whenever it gets a superficial scratch.
01:36But if chromium is the element that protects the steel, why are there so many different types of stainless steel
01:44on the market?
01:45The answer lies in the other alloying elements that make up each type of steel. The 300 series family,
01:52which includes the well-known grade 304, has nickel as its main alloying element. Nickel is the element
02:00responsible for giving these steels their austenitic structure, which ensures ductility, toughness,
02:07mechanical strength and excellent forming properties. Grade 304 typically contains about 18%
02:14chromium and 8% nickel in its composition. However, the 200 series family, which is also austenitic,
02:24replaces some or all of its nickel with manganese. This substitution was developed as a lower cost
02:32alternative since nickel is an expensive commodity whose price fluctuates sharply on the international
02:39market. And why is this a problem? The truth is that a good part of what has arrived on the
02:45Brazilian
02:46market under the name of 200 series stainless steel does not follow any national or international standard.
02:54Materials are being sold as stainless steel with nickel content of approximately around 1%,
03:01a value that does not correspond to any specification found in the standards that govern
03:07stainless steels, such as ASTM A240, to compensate for the drastic reduction of nickel.
03:15These materials are produced with high levels of manganese and copper, as well as low levels of
03:22chromium, which represents a major concern for the durability of these materials.
03:28But how does this difference in composition affect corrosion resistance in practice?
03:36There is a formula used in engineering to estimate resistance to pitting corrosion, which creates small
03:43holes on the metal surface that can eventually penetrate it. This formula is called PREM, which comes from English
03:54pitting resistance equivalent number, and is calculated as follows. The percentage of chromium plus 3.3 times the
04:07percentage of molybdenum plus 16 times the percentage of nitrogen. Here, I have to point out that there are
04:15some variations of this formula, like when we have tungsten in the composition, and when we are dealing with
04:21duplex steel. Then the formula changes a little, but in general, we can use the formula that I mentioned. And
04:28the point is, the higher the result, the better the theoretical corrosion resistance.
04:34According to chemical analysis, the 200 series steel has about 2.5 less chromium than the grade 300 full
04:43stainless steel, which already puts its PRM value at a disadvantage from the start. And there are other
04:51factors that make the situation worse. The sulfur present in these steels combines with the manganese,
04:57which is abundant, forming manganese sulfides. These sulfides in solution can dissolve creating
05:05preferential points for the onset of pitting corrosion. Higher carbon content
05:11can also affect the material's performance regarding corrosion resistance. Higher carbon can compromise
05:19performance in welded regions because it causes the precipitation of chromium carbides at the grain
05:26boundaries, which can trigger intergranular corrosion. Type 304 Aero steel, on the other hand, has low carbon content,
05:35which eliminates this type of problem. But hey, is this whole difference just theoretical? Or does it show up in
05:43real tests?
05:44Well, through corrosion tests carried out with the support of IPT, which is the Institute for Technological Research of Sao
05:52Paulo,
05:53it was possible to compare the performance of the 200 series steels against the 304 under controlled exposure conditions.
06:02of the tests carried out, it was the salt spray test standardized by ASTM B117, which consists of exposing
06:12the samples to an atmosphere with sodium chloride mist at 5% for prolonged periods, after 1000 hours of exposure.
06:22In this test, the 304 steel tubes did not show any apparent corrosion, while the tubes from the 200 series
06:30showed visible corrosion. With several pits, and especially in the welded region, Professor Zezebur Panossian,
06:39who is a researcher at IPT, is one of the leading experts in corrosion in Brazil.
06:44And she has warned about the superiority of 304 steel and the fragility of materials that come to the market,
06:54like the 200 series,
06:56especially when we talk about corrosion resistance and compliance with the standards that govern stainless steel.
07:04In one of the documented cases, the equipment had a support made of AISI 304 steel with no apparent corrosion,
07:13while the connected tube, made of 200 series steel with low nickel content, already showed several corrosion pits.
07:22But if these steels are so different, why is it so hard to tell them apart visually?
07:28It's exactly because visually they are practically identical, and that's why the problem becomes so serious.
07:35Many people buy products believing they are made of 304 steel, and end up receiving 200 series steel, without noticing
07:44the difference.
07:44The result is premature failures and a shorter than expected lifespan, with the appearance of rust spots and corrosion in
07:53chemical equipment.
07:54They should last for many years. So, how can we know if we are really buying 304 steel?
08:01And this is where I want to show you that there is a practical, quick, and low-cost method that
08:09anyone can use.
08:10The pickling gel test.
08:12This gel is an acidic mixture, usually made up of hydrochloric acid, nitric acid, and hydrofluoric acid.
08:19And it can be found in specialized stores.
08:22But before showing the test, it's essential to talk about safety.
08:26This pickling gel is a chemical product, dangerous, corrosive, and it emits fumes that should not be inhaled.
08:35If you are going to replicate this test, it's mandatory to use personal protective equipment.
08:40The procedure must be done in a well-ventilated area,
08:44and the gel should not come into contact with the skin or the eyes.
08:49With that warning given, let's move on to the test.
08:52First, we clean the surface of both plates with any degreaser.
08:56You can even use detergent to remove grease and dirt.
09:01Next, we apply a thin layer of pickling gel on each plate.
09:06On 304 steel, the gel hardly reacts in the first few seconds.
09:12The surface keeps its original appearance without any visible change.
09:16But the magic happens here.
09:17Because on 200 series steel, the reaction is almost immediate.
09:24The gel starts to bubble, and gases are released.
09:28And in a few seconds, a dark stain appears, with greenish tones.
09:32This difference in reaction happens because the chemical composition of the 200 series,
09:39with its high manganese content and low chromium and nickel content,
09:44makes the material much more susceptible to corrosion,
09:47and, consequently, to the action of the acids present in the gel.
09:51The contrast between the two plates is so evident,
09:54that the result appears in less than a minute.
09:57After recording the result with a photo,
10:00let's remove this gel by washing the surface under running water,
10:04and dry it with a cloth.
10:07After washing and drying, what did we learn from this procedure?
10:12We learned that there are reliable ways to verify the origin
10:15and legitimacy of the materials we acquire,
10:19avoiding being deceived or taking risks with our products.
10:23If you invest in equipment, furniture, or stainless steel structures,
10:27expecting durability and corrosion resistance,
10:30with CV 200 series steel instead of 304,
10:34it represents a loss, both financially and functionally.
10:40200 series steel has its legitimate applications,
10:44as long as it is properly specified and used in environments
10:47that do not require high corrosion resistance.
10:49The problem is when it is sold as 304,
10:54deceiving the consumer and compromising the safety and durability of the product.
11:00We have been making this kind of video,
11:02because we have noticed that with the increase in imports into the country,
11:05many products are being sold as 304 stainless steel might of menu,
11:10but in reality, they are actually 200 series steel might of menu steel,
11:15and this directly impacts the quality and especially the cost.
11:19Your opinion is important to us.
11:21So, if you like the video, subscribe to the channel if you haven't already.
11:24Give the video a like and turn on the notification bell.
11:28And if you want to help us produce this and many other pieces of content here on the platform,
11:33consider becoming a member and buy us a coffee and some cheese bread and be remembered in our videos.
11:40If you want to learn more about stainless steel,
11:43and how you can differentiate and identify real stainless steel, check out the Inox de Verdade website.
11:50Here, via the QR code on the side, or in the link in the video description,
11:55where you'll find several articles, myths, interesting facts and many other pieces of information.
12:01To bring this content to you, we used the information that's on this website and in some articles,
12:07as well as having a chat with them, to be able to put together this experiment,
12:11comparing different types of steel with pickling gel.
12:15If you have doubts about this steel, or if by any chance you bought stainless steel that seems fake,
12:22it's worth visiting the website and seeking real knowledge that adds value.
12:27Now, I want you to help us in the comments by telling us if you've ever bought a stainless steel
12:31product
12:32that showed rust earlier than expected.
12:36And if you had already heard about this difference between 304 and the 200 series.
12:44Or maybe, have you ever had the chance to test the quality of steel with pickling gel?
12:48Leave it here in the comments, because I want to know.
12:51On the side here, there are two interesting video options that you need to watch
12:55to expand your knowledge and explore your curiosity.
12:57And if you want to support us, give this video a like, subscribe to the channel,
13:01turn on the notification bell, and consider becoming a channel member.
13:04That's it, engineering lovers, sending you a big hug, and I'll see you in the next video.
