海角社区

Alloys with more than 10.5% chromium are referred to in Sweden as "stainless steel". In many other countries, this type of alloy is referred to as "spotless steel". A common misconception is that stainless steel is completely resistant to corrosion, but this is not the case. All steel products, regardless of alloy, can corrode 鈥� different alloys have different corrosion resistance depending on their composition and the surrounding environment. Alloys classified as stainless steel are to some extent "self-healing", which means that they can partially recover from the attacks they are exposed to. In fact, it is a thin and invisible layer of oxides that form on the surface and make the steel more resistant.

However, corrosion can occur in stainless steel alloys, often as Spot corrosion. This type of corrosion is more difficult to detect than superficial corrosion, which for galvanized products is a clear indication that maintenance is required. Therefore, care should be taken in certain types of environments when choosing stainless steel alloy products. For example, in environments with a high chloride content or high levels of sulphur oxide, careful consideration is required when choosing an alloy. In some cases where inspection and maintenance can be done in a simple way, a hot-dip galvanized product that more clearly reveals its condition may therefore be a better option from a total cost perspective. Below is an example from the Netherlands when a suspended ceiling collapsed in a chloride environment after stainless steel threaded rods corroded.

Figure 1: June 2001, the morning after the collapse of ceiling and air channel in the indoor swimming pool at Steenwijk (NL). The collapse were caused by environmental cracking of stainless steel threaded bars. (Photo courtesy Steenwijkerland municipal)

Figure 2: Phases of pitting corrosion on stainless steel.

*Point corrosion is when the oxide surface of stainless steel is broken. Corrosion that is difficult to detect for the eye then occurs as small holes in the material. The process can then continue inside the surface layer and weaken the product from within.

SS-EN 1993-1-4 helps you choose the right stainless steel grades for specific environments. The standard defines environments from "Rural environment" to "Marine environment".

Based on these categorisations, you can deduce which alloy(s) are most suitable for a specific environment. This table, which is part of Eurocode, is an accepted guide when choosing an alloy in the environments that require a stainless steel product.

Figure 3: Extract from the SS-EN 1993-1-4 Annex A

With the help of SS-EN 1993-1-4 Annex A, you can make a more comprehensive evaluation of the environment, which includes developing a corrosion resistance factor (CRF). This factor is compared to the corrosion resistance class (CRC) of the product. The standard also takes into account aspects such as exposure to sulphur dioxide and maintenance.

Maintenance can extend the intended life of a product. Aspects such as the scope of the inspection, the cleaning method and the time interval must then be clearly stated in the documents. Thus, through regular inspections and cleaning, the corrosion resistance factor can be improved, so that a simpler and more cost-effective alloy can be used. Our experience is that SS-EN 1993-1-4 Annex A is often taken into account in projects where we have high corrosivity, such as road tunnels and certain types of industries. Environments where CRF IV or CRF V resistant alloys are required.

Figure 4: List of stainless steel grades in the corrosion resistance classes based on.

海角社区 offers a wide range of stainless steel products in different corrosion resistance classes. We categorize our products into A2, A4 and A5. The majority of our stainless steel fasteners are classified as A4 (CRC III). A4 products are often the most suitable for different types of outdoor environments, but also in industrial and marine environments. Examples of A4 quality products include our HST3-R and HUS4-HR mechanical fasteners.

We also offer products in A2 and A5 categories, where those belonging to the A5 class are called "HCR" (High Corrosion Resistance Steel) and are included in corrosion resistance class V. An example of a product is HST-HCR. Chemical fasteners are also good choices in corrosive environments. It is a flexible option considering that the anchor compound can be combined with a variety of threaded rods in a variety of galvanized and stainless steel grades. The easiest way to find stainless steel fasteners is to look for an R at the end of the name of our mechanical fasteners and A2, A4 or A5 for threaded rods.

Figure 5: Classification tree for the different stainless steel grades.