How to recognize steel tube failure？

Steel pipe corrosion is a diffusion-controlled process on exposed surfaces, which converts a refined metal to a more chemically-stable form, such as its oxide, hydroxide, or sulfide. It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. In the steel and iron industry, most types of steel tube corrosion come with a continuous and virtually unstoppable process. Corrosion degrades the useful properties of steel pipes including strength, appearance and permeability to liquids and gases.

Most people commonly believe that many structural alloys corrode merely from exposure to moisture in air. Nevertheless, the corroding process starts in essence from the strong reaction with certain substances in environments. Here we would like to talk about a few common steel pipe failures in applications.

1. Uniform corrosion

Uniform corrosion or general corrosion, is defined as a type of corrosion attack (deterioration) that is more or less uniformly distributed over the entire exposed surface of cold rolled steel pipe. Uniform corrosion also refers to the corrosion that proceeds at approximately the same rate over the exposed metal surface. Specifically, cast irons and steels corrode uniformly when exposed to open atmospheres, soils and natural waters, leading to the rusty appearance.

2. Interior Pipe Deposits

For round steel pipe in applications, internal rust deposits, commonly termed tuberculation, are an inevitable death sentence for most piping systems. They are the lighter and less dense end product of steel tube corrosion. Once established by high and uncontrolled corrosion conditions, internal deposits initiate much greater deep pitting. The highest corrosion loss is more likely at horizontal lines and in low flow or dead end areas where rust and other deposits will settle, but can affect vertical lines and main risers as well. Random areas of high tuberculation are actually the result of a high pitting or cell corrosion condition directly beneath it, with the volume or height of the rust deposit directly proportionate to the depth and volume of pipe wall loss.

3. Weathering Damage

Generally speaking, weathering damage subject to rain, snow, atmospheric conditions, or cooling tower, overspray is the easiest to prevent. The piping is exposed and accessible, with corrosion activity always visually obvious. Most weathering damage requires decades to produce a failure, and is simply due to a lack of maintenance. Smaller diameter piping is always most vulnerable due to its inherently lesser wall thickness.

Of course, with regard to different types of pipe corrosion & failure in use, pipe repair work usually takes on various forms, ranging from temporary clamps to the replacement of entire piping systems. On the other hand, steel pipe manufacturers have various kinds of methods of surface treatment for steel tube done as precautions in a mill.

How to make galvanized coating for steel pipe?

How to make galvanized coating for steel pipe？

As it is well acknowledged, galvanized steel pipe is a steel pipe that has been coated with zinc in order to form certain protective layer on the surface of pipe. This coating generally protects the steel from corrosion. Hot dipped galvanized steel pipe is one typical pipe of galvanized pipes in the steel pipe market. As a rule, before the production of galvanized steel pipe, steel materials are placed into a molten bath of zinc. And this process is also called hot dip galvanization. Normally, the two kinds of metals are chemically bound to one another in this processing, and will therefore never separate, resulting in a more resistant and longer lasting version of steel at a mill.

Today, hot dipped galvanized steel pipe has got a large sales share both in the domestic and foreign steel pipe market. Furthermore, due to its wide range of practical applications, galvanized pipe has won the favor of users in the real life. When it comes to galvanized steel pipe, we have to say about its long story of processing technology in history. According to reliable written records, the process of galvanization was first discussed by scientists in the 1770s, nearly 60 years before it was finally introduced in the 1830s. French engineer Stanislaus Tranquille Modeste Sorel took out the first patent for the process in 1937, and began manufacturing it soon after. By the 1850s, Europe was producing galvanized steel out of manufacturing plants located around the continent. The United States followed shortly thereafter, opening its first plant in the 1870s.

In the actual process of the production of galvanized steel pipe, it is necessary for steel pipe manufacturers to have certain professional knowledge of the galvanized coating. In general, factors influencing the thickness and appearance of the galvanized coating include chemical composition of the steel materials, steel surface condition, cold-working of steel prior to galvanizing, bath temperature, bath immersion time, bath withdrawal rate, and steel cooling rate. With reference to the coating thickness, the American Society of Testing and Materials International (ASTM), the Canadian Specification Association (CSA) and the American Association of State Highway and Transportation Officials (AASHTO) specifications establish minimum standards for thickness of galvanized coatings on various categories of items. These minimum standards are routinely exceeded by galvanizers due to the nature of the galvanizing process. On the other hand, the thickness of the zinc layer will also make certain effects on the steel pipe price in the market.

At the end, we have to say that the differences in the luster and color of galvanized coatings do not significantly affect corrosion resistance. The presence or absence of spangle has no effect on coating performance. The well-known spangled appearance found on galvanized products is a crystallization process dependent upon the zinc bath chemistry, the rate of cooling, the method of pickling, the steel chemistry, and the thickness of the coating. Dull gray or patchy matte gray galvanized coatings give a service life equal to bright or spangled coatings since the service life depends on the zinc coating thickness.