The importance of pipeline anti-corrosion and material selection and application
- May 30, 2018 -

In recent years, with the acceleration of the construction of long-distance natural gas, oil pipelines, and urban natural gas pipeline networks in China, the use of pipeline oil, gas, water, and other chemicals is the safest and most effective method, and steel pipeline transportation is also a safe and effective method. It is also one of the oldest methods of application history.

Steel pipelines must be well-preserved to ensure proper transport and operation. The service life of the pipeline depends largely on the material and the method of corrosion protection. Therefore, the rational choice of anti-corrosion materials is very important. The huge investment in pipeline engineering and the external anti-corrosion layer are the basic protective measures for modern pipelines. However, the cost of construction of the anti-corrosion layer accounted for only a small part of the total cost of the pipeline, and it was less than 5% of the total investment, but it played a role of more than 5%! It is directly related to the lifeline of the pipeline, and it is not handled properly. The loss of life and property will be incalculable!

The modern pipeline buried exterior coating is not a situation where petroleum asphalt dominates the world. There are now: coal tar enamel, epoxy coal tar, two-layer PE, fused epoxy powder (FBE), three-layer PE and polyethylene/polypropylene Adhesive tapes (cold tapes) are used in different projects. The following describes the advantages and disadvantages of several materials:

asphalt

Hot-water anti-corrosion of bitumen was applied to the former Soviet Union in the early 50s. Advantages: Low cost, easy construction and safer than coal tar enamel. Defects: high water absorption. Bacterial feeding and poor mechanical properties, labor intensity, low peel strength, environmental pollution and so on.

Coal tar enamel

Before the 1950s, anti-corrosion coated coal tar enamels were mainly used, and their advantages such as high mechanical strength and good corrosion resistance were widely used, and because of the volatilization, toxicity, long curing time, and environmental pollution of the smoke in industrial production. Heavy defects are gradually replaced by other materials.

Epoxy coal tar

It has a history of several decades since it was born. It has the advantages of toughness after curing, strong impact resistance, high peel strength, and good anti-corrosion effect. At the same time, there are many disadvantages: long curing time, occupying a large number of yards, a long construction period, strict requirements on the ambient temperature, leakage after molding, high repair rate, and difficult to repair, environmental pollution and so on.

Epoxy coal asphalt has no standard and detection method for epoxy content. Epoxy is an important part of the corrosion resistance and composition of the coating. For low-quality projects that artificially reduce the coating's active components and obtain undue profits, there is no detection method. Today, with the rapid development of science, there is no scientific detection method for the coating composition that affects the service life of pipelines. Large-area applications are unscientific, combined with human influences in construction. To speed up the operation, two layers of glass filaments are wound one at a time. The first layer of oil is not painted twice until dry, and then it is air-dried. Leaving the point of leakage, drying the single layer together, the pinhole left by the solvent evaporation becomes a major hidden danger, and the layered curing and multi-layer curing are difficult to identify, especially the coating of good luck to the site. The layer is even more untestable! Epoxy coal tar pitch requires 4 hours for each paint surface at 25 degrees Celsius, 16 hours for hard dry, and a long time for low temperature. Then, how many temperatures do the weather have above 25 degrees throughout the year? Strictly stipulated operations result in long solidification and drying times, making it impossible for large-scale mechanized coating. Today, the construction period is inversely proportional to the profit, which construction team can strictly follow the construction specifications. What about operation?

Fused epoxy powder with multi-layer coating (triple PE)

Fused epoxy powder was popularized in the 1960s. The production process of thermosetting powder coating with one shot and film was used to replace the traditionally used coal tar enamel in the United States. The main advantages: good anti-corrosion effect, chemical resistance, wear resistance, temperature resistance, high oxidation resistance, strong steel bonding strength, and resistance to cathodic disbondment.

Anti-corrosion materials use multi-layer anti-corrosion coating developed in the 80's. The coating is a composite structure anti-corrosion coating composed of epoxy powder, inner adhesive, outer polyethylene or polypropylene layer, which not only solves single-layer epoxy powder The disadvantages of poor impact resistance and high water absorption rate also overcome the disadvantages of poor adhesion of the two-layer PE. At present, in China, the composite structure anti-corrosion coating is generally preferred for anti-corrosion from the aspects of the service life and the anti-corrosion effect.

Although it is a high-performance anti-corrosion technology, there are also technical defects and the quality of materials currently on the market:

technical problem

The thickness of the epoxy powder anticorrosion coating is international standard of 250 microns, which is more than three times the depth of 70 micron at the deepest point of shot blasting. The standard in our country is 150 micron, which is less than three times the 70 micron depth of shot blasting. Secondly, the temperature requirement for epoxy powder coating should reach more than 200 degrees, and many of our anti-corrosion processing companies will control the spraying temperature between 100 and 120 degrees, affecting the condensation strength of epoxy powders, and also in the epoxy powder and PE film. Should use polyethylene graft adhesive, in order to reduce the cost of engineering and many processing companies are now using conventional hot melt adhesive, so that the life of plastic and PE materials are not uniform, the quality of life of hot melt adhesive only 3-5 years, If the pipeline construction is now using spiral welded pipe, the height of the weld is two millimeters, and the T-die winding PE tape cannot completely cover the groove on both sides of the weld and the air cannot be completely discharged. Bogey! If the pipe laid is a large diameter pipe with large diameters encountered in the central groove of the pipe and other hard objects, it will injure the PE and brittle epoxy powder layer, causing pipeline corrosion hazards.

Artificial Qualities Caused by Low-price Bidding

Many projects in project bidding insisted on insisting on the principle of low price winning bids to force bidding companies and raw materials producers to win bids. In violation of economic laws, they reported low prices and made a big fuss about production costs because no one lost money. Will do, thus resulting in anti-corrosion engineering market, many anti-corrosion technology name is not true

Question 1

Epoxy powder with lacquer added 20 to 40 percent talcum powder to reduce the cost of the project. The corrosion-resistant steel pipe using this material was not qualified before being buried in the electric spark test, and was buried underground for a week to decompose the talcum powder. The re-test is all EDM, anti-corrosion effect is completely unqualified.

Question 2

As mentioned above, the two PEs and three PEs widely used in the market are not anti-corrosion effect and life-long grafting adhesives, but are EVA adhesives or ordinary hot-melt adhesives that have a relatively low cost of life and only have a lifespan of 3-5 years. After a few years, loosening of the bone of the PE tape was severed, which seriously affected the quality of preservation.

Polyethylene/Polypropylene Adhesive Tape (Cold Wrap)

In recent years, with the development of science and technology and the improvement of anti-corrosion materials, some units have developed several anti-corrosion tape products, which have been used in many projects. The design units have also selected according to environmental conditions, anti-corrosion requirements and the characteristics of anti-corrosion tape products. set. Its antiseptic structure is divided into:

# Composite structure consisting of primer + anticorrosive adhesive tape (with inner tape) + protective adhesive tape {bandage}

# Preservative structure consisting of primer + anti-corrosion adhesive tape (polyethylene/polypropylene)

Anti-corrosion adhesive tapes are applied to more and more pipeline projects with the advantages of simple construction, long life, economical price, and scientific and environmental protection.

The following describes one of its products: Polyethylene cold tape

This material adopts butyl rubber modified asphalt as anti-corrosion adhesive layer. Its excellent tensile strength and strong adhesive property can effectively resist soil stress, external force, impact and thermal expansion, and prevent deformation and peeling of the anti-corrosion layer. Aging test test proves that the anti-corrosion life span is 40-50 years or more, and each test index is much higher than the SY/T0414-2007 standard, fully meeting the US ANSI/AWWAC209-00 and NACEMR0274-95 indicators. It is praised by the same industry as the "Crown of Anti-corruption" representing the highest level of international and domestic cold-wrapped belts. T-series cold-wound tape products are widely used in petroleum, chemical, natural gas, water supply and drainage in urban construction, oil and gas, gas transmission steel pipelines, and steel buried storage tanks and pipeline repair works. It is recommended by the Ministry of Construction and the State Environmental Protection Administration to replace “asphalt glass cloth” and “epoxy coal pitch”.

The above anticorrosion materials with different anticorrosive materials have different anticorrosive qualities and costs. The selection and application of anticorrosive materials and anticorrosive expenses shall be comprehensively and comprehensively considered according to the different pressures and different uses of the protection pipes and the different environments in which they are transported and the different substances transported.

The basic requirements for the service life of pipelines are more than 30 years. At the same time, the frequency of maintenance should be reduced to ensure safe use for normal use. Therefore, the selection and application of anti-corrosion materials should be highly valued by pipeline builders and designers. The application of materials will have the following trends:

1: easy construction

2: Longer life

3: Cost economy

4: Environmental protection

1. Construction convenience refers to the fact that the steps are simple and convenient, the processing plant and the site can be constructed, and the relatively complicated construction procedures can reduce the difficulties caused by the cumbersome steps and quality control.

2. Longer life expectancy of course, from the original 20-30 years of design life to a longer time to save replacement maintenance and other costs.

3. Cost economy refers to a reasonable ratio of product quality, service life, and investment costs. In simple terms, it is “high quality and low price”.

4. Conformity to environmental protection means that with the progress of the times, environmental protection requirements have become increasingly stringent. Products that fail to meet environmental protection requirements will be gradually eliminated when considering health, safety and environmental factors. Builders must take the initiative to pay attention to environmental protection issues and select materials. Social responsibility.

Pipe anti-corrosion materials and anti-corrosion systems are basically long-acting, and it takes a long time to know the actual results, regardless of petroleum asphalt, coal tar enamel, epoxy coal tar pitch, cold adhesive tape, fused The entire development process of epoxy powder or three-layer PE has experienced long-term practical test, and all materials have different advantages, although "petroleum pitch" "coal tar enamel" "epoxy coal tar pitch" can not be comprehensive in the short term Cancellation, but the future trend of development should be polyethylene cold-wrapped tapes for mainstream products.