Anticorrosion of Steel Pipes for Water Delivery

Jan 28, 2023

1.1 External anticorrosion
The external anti-corrosion of water delivery steel pipes mainly includes 3PE coating and hot-melt PE powder. 3PE coating is a relatively complete and better external anti-corrosion process at present, and its anti-corrosion process is shown in Figure 1. Combining the corrosion resistance of fusion-bonded epoxy powder and the high density of polyethylene anti-collision, the external anti-corrosion has good mechanical properties, good adhesion, good insulation, and low water absorption. It is currently widely used in external anti-corrosion coating for various pipes.

Figure 1

Hot-melt PE powder coating is similar to powder spraying technology. After PE powder is hot-melted, it is 100% bonded to the pipe body, and it is a whole coating. It can realize the consistent structure of the anti-corrosion layer of elbows and pipe fittings and the hot-melt PE of the main pipe. The process of hot-melt PE powder is simple, but the disadvantage is that the adhesion is average; the anti-corrosion layer is thin (1.5 mm), and it is not resistant to damage.

1.2 Internal anticorrosion
With the development of anti-corrosion of the pipeline, there are relatively abundant anti-corrosion forms in pipelines, mainly including lining cement mortar coating, polyurethane coating, solvent-free liquid epoxy coating, FBE coating and IPN8710 coating. FBE epoxy resin inner coating is based on epoxy resin, adding modified quartz sand as filler, and the epoxy powder prepared by grinding is melted and solidified at high temperature, adhering to the inner wall of the steel pipe after heating. It is characterized by a small inner wall friction coefficient (0.0081 to 0.091), lower energy consumption, smooth inner wall, not being easy to scale, no pollution to water quality, and 100% curing, no ester bond after curing, no hydrolysis reverse reaction and anti-corrosion effect not being reduced, long theoretical service life (50 years). The disadvantage is that the steel pipe is heated in the anticorrosion process, so it is limited to large-diameter steel pipes.

The solvent-free liquid epoxy inner coating is fully automatic high-pressure spraying without gas at room temperature, and the solvent-free two-component epoxy coating is sprayed on the inner wall of the steel pipe. The advantage of this kind of inner coating is that it does not contain harmful substances, and has the characteristics of no leakage, environmental protection, good adhesion, long service life, and a thick film formed at one time. IPN-8710 painting is a new generation of non-toxic drinking water special two-component paint developed in combination with epoxy drinking water tank paint. The first component of the paint is composed of modified epoxy resin, polyurethane resin, non-toxic pigments, fillers and additives. IPN-8710 painting is applied to the inner wall of steel pipes by the spraying equipment. The disadvantage is that the paint should be used up within 6 to 8 hours after curing. Otherwise, it is easy to cement, and the construction time is relatively long.

According to the application cases of foreign water pipelines, cement mortar and polyurethane coatings can also be applied to the internal anti-corrosion of water pipelines, but the project cost is relatively high. There are few applications in China. According to foreign introductions, polyurethane coating is a kind of all-round thermosetting plastic coating. It is used for internal and external spraying of pipes and pipe fittings and has advantages of moisture resistance and temperature resistance (withstanding a high temperature of 160°C), and good gloss and color retention, high gloss and decoration of the coating, simple process and fast drying speed. It can also be cured normally at 0 °C, and the film is thick at one time. It is currently expensive, so it is rarely used in China.

In addition, the cement mortar inner coating is to uniformly coat the cement mortar on the inner wall of the steel pipe through the centrifuge in the factory or the pipeline on-site spraying machine. This anti-corrosion method is characterized by low prices of raw materials and low requirements for rust removal on the inner wall of the steel pipe. Cement mortar is used for the anticorrosion of steel pipes for water delivery. When water permeates through the cement mortar layer and reaches the steel surface, it has become an alkaline solution with a high pH, passivating the steel surface, and the cement mortar is closely combined with the inner wall of the steel pipe. The disadvantage is that improper maintenance of cement mortar in the production process is prone to cracks, hollowing and other defects, which will affect the anti-corrosion effect.

To sum up, in terms of the anti-corrosion coating of the pipeline, welded steel pipes are more flexible than PCCP pipes and ductile iron pipes with a single anti-corrosion coating. Flexibly select anti-corrosion coatings that meet the requirements according to the actual situation of the region to meet different requirements for transmission media and environments, ensuring the long-term and safe operation of pipelines.

2. Practical applications
After nearly 60 years of development in China's welded pipe industry, the rapid development of pipe-making technology and iron and steel metallurgy technology has ensured that welded steel pipes have high welding quality and high dimensional accuracy, and have good pressure bearing capacity, excellent deformation resistance, good reliability and safety. Assisted by the anti-corrosion technology of steel pipes, welded steel pipes have been applied more and more in the field of water delivery engineering in recent years. The main projects are shown in Table 2.

Table 1 Municipal water delivery projects using spiral steel pipes for water delivery
Projects

Projects	Diameters of steel pipes/mm	Wall thickness/mm	Anti-corrosion type
Gansu Yintao Water Conveying Project	1220	18/20	External anti-corrosion 3PE, internal anti-corrosion FBE
Yancheng New Water Source and Drinking Water Project	2420	22	External anti-corrosion 3PE and internal anti-corrosion FBE
Guang'an Garden Water Plant Renovation Project	820 to 1220	12	External anti-corrosion 3PE and internal anti-corrosion 8710
Zizhong Chengbei Reservoir Networked Water Supply Project (under construction)	2420	22/20	External anti-corrosion 3PE and weather-resistant double epoxy coating, internal anti-corrosion solvent-free epoxy
	1620	20/16/14
Guodian Nanning Power Generation Co., Ltd. water supply and drainage project	630	10	External anti-corrosion 3PE, internal anti-corrosion 8710
	325	8
	219	6
Tuke Town Ordos Water Pipeline	1220	20/22	External anti-corrosion 3PE and internal anti-corrosion FBE
Luzhou Naxi Shengyuan Hydropower Development Co., Ltd.	1420	14	External anti-corrosion 3PE and internal anti-corrosion 8710
Linxia Yellow River Diversion Project	1124	12	External anti-corrosion 3PE and internal anti-corrosion FBE
Tail water discharge project of the sewage treatment plant in Gui'an New District	1820	20	External anti-corrosion 3PE and internal anti-corrosion 8710
Kaili Tap Water Supply Phase III	820	12.3	External anti-corrosion 3PE and internal anti-corrosion 8710
Bijie Jiayan Water Conservancy Project	1200/900		External anti-corrosion 3PE, weather-resistant double epoxy coating and internal anti-corrosion solvent-free epoxy
Fengshan Reservoir, Qiannan Prefecture, Guizhou	800/1000		External anti-corrosion 3PE and internal anti-corrosion 8710
Shaxi water pipeline	600 to 2 600		External anti-corrosion 3PE and weather-resistant double epoxy coating, internal anti-corrosion solvent-free epoxy

The rapid development of anti-corrosion technology and anti-corrosion materials has made the safe service life of water delivery steel pipes much longer than that of other pipes. In recent years, anti-corrosion steel tubes have been widely used in the field of water delivery.