In addition to the excellent chemical corrosion resistance, strong adhesion, and mechanical damage resistance as the outer wall anti-corrosion layer, the steel pipe lining also needs excellent wear resistance. Polyurethane wear-resistant and anti-corrosion coating materials are different from general wear-resistant Compared with anti-corrosion coating, it has the following characteristics:
1. Good chemical stability: As a long-term anti-corrosion coating, it must have excellent corrosion resistance to ions in chemical media, such as Cl -, S0 42-, Na+, etc. There are different methods and standards for judging the chemical corrosion resistance of coatings. The qualified standard is: the appearance of the coating has no blisters, no cracks, no significant discoloration, no significant softening, and the weight gain rate does not exceed the standard requirements. Within the time specified in the standard, the weight gain rate of the polyurethane coating is far less than the standard requirement, which shows that it has good resistance to strong acids, alkalis, and salt. Such a good chemical corrosion resistance coating material can be used in the transportation of tap water, sewage, seawater, and other media and the embedding of strong corrosive soil.
2. Good water penetration resistance: Whether it is used for external anti-corrosion or inner wall anti-corrosion of buried pipelines, water penetration resistance is the most basic requirement of anti-corrosion coatings and the main index to measure anti-corrosion coatings. In the aqueous solution of inorganic substances, water molecules are the liquid medium with the smallest volume, and their permeability is stronger than that of ordinary ions. The general rule of organic coatings is that they are impermeable in seawater, next in tap water, and worst in distilled water. Therefore, the penetration ability of the coating in distilled water or dilute saline solution directly reflects the compactness of the coating.
3. Polyurethane coating has high mechanical properties: In addition to good anti-corrosion properties, the anti-corrosion coating of steel pipes must also have good adhesion and certain mechanical strength. Whether the cured coating can be firmly attached to the steel pipe substrate is the key factor for whether the coating can play a protective role. In addition, the coating also needs to have a certain mechanical strength, which can withstand the impact during transportation and installation, and ensure that it can withstand the stress under working conditions, such as the deformation of the pipe during the embedding process. Polyurethane coatings still have high adhesion and indentation hardness at high temperatures, ensuring the long-term use of coatings; compared with imported coatings, domestic coatings have relatively low adhesion, and it should be noted that the quality of surface treatment will also affect the adhesion of the coating.
4. The polyurethane coating has good erosion and cavitation resistance: the inner wall of the steel pipe is eroded by flowing water, and there are corrosion and mechanical wear at the same time, and the two accelerate each other. The main forms of wear are impact corrosion (erosion) and cavitation corrosion ( Cavitation) and mechanical abrasion. Erosion is caused by water turbulence or impact; cavitation is due to high-speed flowing liquid, which produces so-called cavitation due to irregular flow. There is only a little water vapor or low-pressure air in this cavity. Due to the frequent changes in pressure and flow conditions, the cavity will periodically appear and disappear. When it disappears, due to the large pressure difference with the surrounding high pressure, it is close to the cavity The so-called “water hammer effect” occurs on the metal surface, which often destroys the protective film on the metal surface and accelerates corrosion; mechanical abrasion is caused by the high-speed impact of solid substances such as water and sand particles on the metal surface, which is similar to the principle of “water drop through stone”. The steel pipe is inevitably mixed with mud, sand, and gravel. In this environment, the coating is subjected to the interaction of the erosion and abrasion of the solid-liquid two-phase flow and the chemical corrosion of the medium in the water. This requires the anti-corrosion lining to have excellent erosion resistance, Abrasive, and cavitation. Polyurethane lining has good abrasion resistance, which is determined by the inherent characteristics of polyurethane, which has been widely used in wear-resistant linings.
5. Good hydraulic performance: For pipelines, the smoother the coating, the smaller the resistance of transportation, which can reduce the power of power, which also reduces energy consumption and improves power efficiency. After spraying the polyurethane lining coating, the inner surface roughness can be reduced from 0.03 to 0.04mm to 0.0025mm, and the n value is between 0.0085 and 0.0089. Compared with the steel pipe lined with cement mortar, it can significantly reduce the liquid pressure loss along the way, The same amount and same diameter water delivery can reduce energy consumption by 30-40%. In addition, since the polyurethane coating is fully cured, does not contain solvents, and the coating surface is well sealed, it is not easy to scale and can maintain the smoothness of the inner wall for a long time.
6. The coating has good bending resistance:
The need for polyurethane lining to have a certain degree of bending resistance is mainly determined by two factors. On the one hand, due to handling, the polyurethane lining pipe may drop or be subjected to external collisions, causing slight plastic deformation, which may cause damage to the lining; On the one hand, the bending moment of the ductile iron pipe caused by ground depression or different degrees of settlement may also lead to the failure of the lining. Therefore, the polyurethane lining for steel pipes must have good bending resistance. The indirect impact is a good detection method. According to the requirements of the standard EN15655, the polyurethane lining must be able to withstand at least 50J of reverse impact energy without causing damage to the lining. Damage is required.
Post time: May-08-2023