How to avoid corrosion on pipe flanges?

What is pipe flange corrosion?

Corrosion is common in oil and gas pipelines, especially when they are located near water. Oxygen in the water will combine with metal molecules and then form corrosion. This chemical reaction will gradually destroy the material, which is why it is so important to use tight-fitting gaskets and seals. Usually, corrosion occurs inside the pipe flange, but the outside may remain uncorroded. This is why the problem is not always noticed immediately, which may lead to further problems later.

The main causes of pipe flange corrosion include environmental factors, improper material selection, improper installation and maintenance, etc. ‌

1. Environmental factors
‌Corrosive environment‌: The flange installation environment has corrosive environments such as sewage, high temperature, acid and alkali, which will cause the flange surface to begin to corrode and form rust‌.

‌Humidity and temperature difference‌: In high humidity environments and large temperature differences between day and night, especially when the relative humidity reaches or exceeds 70%, water vapor and oxygen on the metal surface combine to accelerate the oxidation process and form rust‌.

2. Improper material selection
‌Contact material mismatch‌: During the installation or maintenance of the flange, tools or materials that do not match the flange material are used, resulting in scratches or damage on the flange surface, accelerating the occurrence of rust‌1.

3. Improper installation and maintenance
‌Poor sealing‌: The flange and gasket are not tightly sealed during installation, or it is installed near a water source, causing moisture to penetrate into the flange and accelerate rust‌.
‌Inadequate maintenance‌: Insufficient regular maintenance, and failure to remove sewage and sediment around the flange in time, resulting in environmental impact on the flange and accumulated dirt accelerating rust. ‌

The importance of flange corrosion prevention:
One of the reasons why corrosion has received widespread attention in the oil and gas industry is that it can be extremely dangerous. Acid corrosion occurs when there are acidic liquids and gases at higher temperatures in the pipeline. The severity of corrosion depends on the operation and environment, but it also varies depending on the different liquids transported through the pipeline. When seal rust occurs, it is usually difficult or impossible to repair, which is why you need to prevent this from happening in the first place.

Flange fittings are an integral part of any pipeline. Flanges on natural gas pipelines must withstand pressures of up to 1500 psi. Of course, by the time the gas reaches its destination, the pressure will have dropped to about 0.25 psi. Corrosion can significantly reduce durability. There are several ways to avoid flange corrosion.

Pipe Flange Corrosion Types and Prevention Methods:

Types of flange corrosion:

The two most likely types of corrosion on pipe flanges are pitting and crevice corrosion.

1) Pitting: Pitting occurs on the flange face and usually appears in groups or clusters. This type of corrosion can cause small cavities or pits to form on the surface of the material. Choosing the right alloy is one of the best ways to prevent pitting.

2) Crevice corrosion: Crevice corrosion is more difficult to detect and therefore more dangerous. This type of corrosion occurs where two flanges meet, and crevice creep occurs when concentrated material accumulates between two adjacent flanges. This type of corrosion can be very destructive because it is not easy to inspect the area where it occurs, and it will eventually cause extensive damage.

Currently, the method of monitoring flange pipe damage is to disassemble the joint and visually inspect the surface. This method is not ideal due to the reduction in cost and time. Some progress has been made using some non-destructive techniques to check the degree of corrosion on the flange.

Methods for preventing flange corrosion:

1. Flange inspection
Unprotected flanges face a higher risk of corrosion and failure. Regular inspections are required to ensure availability. The destructive inspection process can cause downtime and is very time-consuming. Completely corrosion-proof flanges mean fewer inspections, less downtime, and less inspection time.

2. Paint Solutions
Anti-corrosion paint solutions are one of the most common ways to prevent corrosion. Anti-corrosion paints are typically polyurethane or epoxy paints. Most anti-corrosion paints bond directly to the substrate to form a hard coating. When using anti-corrosion paints, it is important to apply the right amount of paint. If the paint is too thin, the area will be ineffective; however, if the paint is too thick, it can cause fasteners to seize.

Because there are many different flange shapes and angles, you may not be able to paint the entire area. After the flange is inspected, another coat will need to be applied. The benefit of using anti-corrosion paints is that they do not require specialized equipment or hot work. However, they do not reduce the need for regular inspections. In addition, you will need to develop a paint maintenance plan to ensure continued protection.

3. Mechanical Solutions
One of the simplest ways to prevent flange corrosion is to add gaskets to the unit. Gaskets can prevent corrosion by providing a barrier between the flange and the corrosive chemicals.

Selecting the right flange gasket can help prevent corrosion caused by corrosive chemicals. Flange faces are also different, and the gasket must match the appropriate flange face type. When dealing with chemical oxidants/HF acids, it is critical to choose a strong gasket that helps prevent corrosion. Mechanical solutions require less maintenance than chemical or paint solutions.

4. Use tape
Using tape is also one of the common methods, whether semi-solid or fully solid. Tape can consist of viscoelastic polymers, wax, petroleum jelly embedded in a fabric for wrapping. These methods are particularly suitable for the waterproof properties of semi-solid polymers, although they may be less common in high-pressure applications.

All prevention methods have their own advantages and disadvantages. No one solution can completely prevent corrosion from occurring. However, regular inspection and maintenance can help prevent rapid corrosion and encourage general maintenance.

Methods to repair corroded flanges:

There are three main methods that can be used to repair corroded flanges:

. Add polymer composites to rebuild the flange face.
. Add material to the ring groove or sealing surface and then machine it within the flange tolerance.
. Remove the damaged flange and weld a new one (safest option).

Factors that affect the corrosion resistance of flanges under operating conditions:

. Temperature of the corrosive agent
. Purity of the corrosive agent
. Concentration of the corrosive agent

Contact an industry expert!

Let us help you find the best quality flanges for pipe fittings. A great way to prevent corrosion is to choose the right flange for the application from the beginning. High-quality flanges made for a specific application are an important first step in preventing corrosion and other failures. Make sure you buy flanges from a trusted source like Hunan Standard Steel Co., Ltd. If interested, please contact: sales@hu-steel.com

Read more: Pipe flange size specifications and classification or Pipe flange material selection