SMLS Steel Pipe Internal Corrosion Treatment

The internal corrosion protection treatment of smls steel pipes is a crucial part of pipeline engineering, especially for transporting corrosive media (such as H2S and CO2 in crude oil, natural gas, chemical products, sewage, etc.) or for occasions where there are high requirements for the purity of the media (such as drinking water). The purpose of internal corrosion protection is to protect the inner wall of the steel pipe from the corrosion of the medium, extend the service life of the pipe, ensure the quality of the conveying medium, and reduce the operating and maintenance costs. The following is the carefully summarized information on the corrosion protection treatment of seamless steel pipes.
 
Why do internal corrosion treatment be required?
 
Although seamless steel pipes themselves have excellent structural uniformity and pressure bearing capacity and do not have the corrosion risks caused by welds, their steel body will still be corroded in a specific environment. The internal corrosion protection mainly solves the following problems:
 
Media corrosion: The fluids (liquids, gases or slurries) conveyed may contain corrosive components such as acids, alkalis, salts, water, oxygen, hydrogen sulfide, carbon dioxide, chloride ions, etc.
Wear corrosion: In addition to chemical corrosion, physical wear will also be accompanied by slurry.
 
Biocorrosion: Microorganisms present in certain media can cause pipeline corrosion.
Media contamination: The corrosion products of the inner wall of the pipeline will enter the fluid and contaminate the media (such as drinking water, food-grade products).
Increased fluid resistance: Corrosion products and scaling will increase the roughness of the inner wall of the pipe, increase fluid resistance, and reduce conveying efficiency.
Extend life: Effective internal corrosion protection can significantly extend the service life of the pipe and reduce the frequency of replacement and repair.
 
Common methods of anti-corrosion treatment for seamless steel pipes
 
There are many internal corrosion treatment methods for seamless steel pipes, mainly based on the properties, working temperature, pressure, economy and service life requirements of the conveying medium.
 
1. Liquid Epoxy Coating: One or more layers of liquid epoxy resin coating are sprayed on the inner wall of the steel pipe. The epoxy coating has excellent adhesion, corrosion resistance, wear resistance and dielectric properties.
 
2. Fusion Bonded Epoxy, FBE: Preheat the steel pipe to a certain temperature, and then spray the epoxy powder onto the inner wall, which melts, levels and cures at high temperatures to form a continuous coating. It is mainly used for internal corrosion prevention in long-term pipelines such as oil, natural gas, and drinking water.
 
3. Cement Mortar Lining: Spray or centrifuge a layer of cement mortar (usually a mixture of high-grade cement and fine sand) on the inner wall of the steel pipe. It is mainly used for pipes that transport water and sewage and other water-quality media.
 
4. Fiberglass Reinforced Plastic Lining, FRP: Make or install a layer of glass fiber reinforced plastic (Fiberglass) composite material on the inner wall of the steel pipe. It is used to transport highly corrosive media such as acids, alkalis, brine, sewage, etc.
 
5. (Plastic Lining) / Rubber Lining: Combine plastics (such as polyethylene PE, polypropylene PP, polyvinyl chloride PVC) or rubber with the inner wall of the steel pipe by physical or chemical methods. Plastic lining is often used to transport water and weak acid and alkaline medium; glue lining is used to transport abrasive or highly corrosive medium.
 
6. Inorganic Zinc-Rich Coating: Spray an inorganic silicate coating containing a large amount of zinc powder, which provides sacrificial anode protection in the coating. It is mainly used in pipes in seawater or freshwater environments as anticorrosion primer.
 
Overview of internal anti-corrosion construction process flow (taking coatings as an example)
 
Although the specific types of coatings are different, internal corrosion protection construction usually follows the following basic steps:
 
1. Pipe section preparation: The seamless steel pipe to be processed should be a finished pipe that has passed the inspection.
 
2. Surface treatment: This is the key to internal corrosion protection construction.
Oil removal and decontamination: Remove impurities such as oil, dust, etc. from the inner wall of the steel pipe.
Sand blasting and rust removal: Use high-speed spray abrasives (such as steel sand, quartz sand) to thoroughly clean the inner wall of the steel pipe to remove the scale, rust and old coatings to achieve the required cleanliness (such as Sa2.5 or Sa3).The surface after sandblasting will form a certain roughness (anchor pattern depth), which is conducive to the adhesion of the coating.
3. Dust removal: Remove the abrasive and dust remaining in the tube after sandblasting.
4. Heating (optional): Some coatings require preheating of steel pipes before construction to ensure the fluidity of the coating and curing quality.
 
5. Painting: Coating mix: Mix the coating according to proportions.
Spraying equipment: Use a dedicated inner wall spraying equipment (such as a rotary spray gun) to spray the paint evenly on the inner wall of the steel pipe. For long pipes, spraying may be required through the pull nozzle.
Multi-layer coating: According to the design requirements, it may be necessary to apply in multiple layers, and the coating interval between each layer must comply with the requirements of the paint manufacturer.
 
6. Curing/Maintenance:
Cooling at room temperature: Most paints cure at room temperature.
Heating curing: Powder coatings such as FBE need to be melted and cured at high temperature.
Wet maintenance: The cement mortar lining requires a certain amount of humidity for maintenance.
 
7. Quality inspection:
Coating thickness detection: Use a thickness gauge to check whether the coating thickness meets the design requirements.
Adhesion detection: Grading method or drawing method to detect the adhesion between the coating and the steel substrate.
Electric spark detection: Check whether there are any leakage points or pinholes on the coating to ensure the integrity of the coating.
Appearance inspection: Check whether the coating is uniform and flat, and whether there are any defects such as bubbles and sags.
Curing degree detection: Ensure that the coating is completely cured.
 
8. Repair: Repair the defects found in the detection and test them again.
9. Finished product protection and transportation: Protect the pipe openings of the treated steel pipes to avoid damage during transportation.
 
Read more: How to Correctly Mark SMLS Steel Pipes?