大多数人认为不锈钢是绝对不会生锈的，而生锈的就不是不锈钢了。其实，一些含镍低的不锈钢材质在一定的条件下也会生锈的。不锈钢方管具有抵抗大气氧化的能力，同时也具有在含酸、碱、盐的介质中耐腐蚀的能力。但其抗腐蚀能力的大小是随其钢质本身化学组成、加互状态、使用条件及环境介质类型而改变的。因此，不是任何一种不锈钢，在任何环境下都能耐腐蚀不生锈。
Most people think that stainless steel will never rust, but stainless steel will not rust. In fact, some stainless steel materials with low nickel content will rust under certain conditions. Stainless steel square tube has the ability to resist atmospheric oxidation, but also has the ability to resist corrosion in medium containing acid, alkali and salt. However, the corrosion resistance of the steel varies with its chemical composition, additive state, service conditions and the type of environmental medium. Therefore, not any stainless steel, in any environment can resist corrosion and rust.
Square tube
不锈钢是靠其表面形成的一层极薄而坚固细密的稳定的富铬氧化膜来防止氧原子渗入氧化，而获得抗锈蚀的能力。该薄膜如果遭到破坏，不锈钢方管就会失去抗锈能力。日常中多见的破坏方式有如下四种：
Stainless steel is formed by a very thin, solid, compact and stable chromium-rich oxide film on its surface to prevent oxygen atoms from penetrating into oxidation, and to obtain the ability to resist corrosion. If the film is destroyed, the stainless steel square pipe will lose its rust resistance. There are four common ways of destruction in daily life:
（一）不锈钢方管表面粘附有机物汁液，在有水氧情况下，构成有机酸，长时间则有机酸对金属表面的腐蚀。
(1) The surface of stainless steel square tubes is adhered with organic juice, which forms organic acids in the presence of water and oxygen, and corrodes the metal surface for a long time.
（二）在有污染的空气中，遇冷凝水，形成硫酸、硝酸、醋酸液点，引起化学腐蚀。
(2) In polluted air, when it encounters condensate water, it forms sulfuric acid, nitric acid and acetic acid liquid points, which cause chemical corrosion.
（三）不锈钢方管表面存积着含有其他金属元素的粉尘或异类金属颗粒的附着物，在潮湿的空气中，附着物与不锈钢间的冷凝水，将二者连成一个微电池，引发了电化学反应，保护膜受到破坏，称之谓电化学腐蚀。
(3) The surface of stainless steel square tubes contains dust containing other metal elements or adhesives of different metal particles. In humid air, the adhesives and the condensate water between the adhesives and stainless steel connect the two into a micro-battery, which causes electrochemical reaction and damages the protective film. It is called electrochemical corrosion.
（四）不锈钢方管表面粘附含有酸、碱、盐类物质，引起局部腐蚀。
(4) The adherence of stainless steel square tubes to the surface contains acids, alkalis and salts, which causes local corrosion.
