3PE anti-corrosion steel pipe refers to 3-layer structure polyolefin coating (MAPEC) external anti-corrosion erw steel pipe, which is a commonly used anti-corrosion pipe in China. Generally refers to the outer wall of steel pipe anti-corrosion. Others include IPN8710, FBE epoxy powder, and epoxy coal tar pitch. 3PE anti-corrosion generally consists of three layers of structure: the first layer of epoxy powder (FBE>100um), the second layer of adhesive (AD) 170~250um, the third layer of polyethylene (PE) 2.5~3.7mm, the actual operation of mixing three materials Incorporating into one, it is processed to make it firmly combined with steel pipe to form an excellent anti-corrosion layer. The processing method is generally divided into two types: winding type and round mold coating type.
2PE/3PE anti-corrosion pipe is suitable for underground coal mine drainage, downhole spray, positive and negative pressure ventilation, gas drainage, fire sprinkler and other pipe networks. Process water waste slag and return water transmission pipeline of thermal power plant. Excellent applicability to water supply lines for anti-spray and sprinkler systems. Cable protection sleeves for electricity, communications, highways, etc. Applicable to high-rise building water supply, heat network heating, water supply engineering, gas transportation, buried water and other pipelines. Process pipelines for transporting corrosive media in petroleum pipelines, chemical pharmaceuticals, printing and dyeing industries. Sewage treatment discharge pipe, sewage pipe and biological pool anti-corrosion project. For agricultural irrigation pipes, deep well pipes, drainage pipes and other networks, it can be said that 3PE anti-corrosion steel pipes are indispensable in the current construction, and it is believed that through the extension of technology, there will be more brilliant achievements in the future.
In the early days of the introduction of 3PE coating technology, China National Petroleum Engineering and Technology Research Institute compiled the first 3PE coating construction acceptance specification in China in April 1995 with reference to DIN30670-1991 and NFA49-710 (March 1988). Construction of pipelines and reservoirs. In the same year, it was upgraded to the industry standard SY/T4013-1995. After several years of engineering construction summary and practice, it was revised to SY/T0413-2002 in 2001 and implemented on August 1, 2002. At the beginning of the standard formulation, according to the actual situation in China, polyethylene is mainly made of high-density polyethylene, and the Vicat softening point is set at not less than 110 °C; the thickness of the outer anti-corrosion layer is based on the German standard of low- and medium-density polyethylene. Determined by DIN30670-1991.
The impact strength of the 3PE anti-corrosion layer was greatly improved, and the construction quality of the Shaanxi-Beijing pipeline and the Kusong pipeline was ensured. SY/T0413-2002 further improved the peel strength and impact resistance of the 3PE anti-corrosion layer, and clearly defined According to the carbon black content of some special materials, the mechanical strength and weather resistance of the 3PE anti-corrosion layer are ensured, and the frequency of the stripping strength (ie, the peel strength of the heat-shrinkable sleeve and the heat-shrinkable strip to the primer steel) is increased.
The contribution to the quality of the anti-corrosion coating outside the pipeline has been contributed. 3Reliable research in response to the disputes over the use of 3PE coatings in China, CNPC Engineering and Technology Research Institute was commissioned by Beijing Huayou Natural Gas Co., Ltd. to complete the “Safety Evaluation of Polyethylene Coatings for the Three-layer Structural System of Shaanxi-Beijing Gas Transmission Pipeline”.The study included the analysis of the results of the excavation inspection and non-excavation inspection of the pipeline outside the pipeline from the foreign literature collection of Beijing Huayou Natural Gas Co., Ltd. from 2001 to 2003, and the unopened open storage of the Shaanxi-Beijing pipeline in North China. The 2PE and 6-year anti-corrosion performance tests of the factory reached the following conclusions:
(1) At present, the evaluation of the application effect of the anti-corrosion layer at home and abroad is very good, and there are few reports on the defects generated in its use. The main shortcomings reported are dew point, stripping, cathodic disbonding, cathodic protection shielding, peeling of anti-corrosion film under the film, etc., and most of the reports on defects still stay in the theoretical speculation stage, such as the mention of cathodic protection shielding problems, There are no examples of cathodic protection shielding in the actual operation of the coating. After years of practice, the coating system with the least defects has been FBE/extruded polyethylene 3-layer structure anti-corrosion system with the increase of service life.
(2) Through the review of the application history of European polyethylene anti-corrosion layer for 30 years, although corrosion or stress corrosion cracking will occur under the anti-corrosion layer theoretically, there is no case of sub-film corrosion or stress cracking under the peeling anti-corrosion layer. . At the Mannesmann Institute in Germany, long-term corrosion laboratory experiments were carried out to simulate the application of anti-corrosion coatings. Corrosion test environment has soil, water, and test main stress corrosion cracking problems. The experimental anti-corrosion is to place the defective polyethylene anti-corrosion layer steel pipe under corrosive conditions and stress conditions.
The corrosive environment is sand environment containing NaHCO3, temperature 70 °C. The tube ground potential is -430~-460mV, the surface of the steel tube is pretreated in different ways, and all the steel tubes are pressurized. At the end of the experiment, there was more or less peeling around the defects of the anti-corrosion layer, but the peeling area was found to be corroded. The steel pipe with no oxygenated skin on the surface is subjected to stress cracking, and the steel pipe with oxide scale is cracked. The maximum crack depth is 0.2 mm, which may be caused by stress corrosion. It is concluded that thorough surface treatment is an effective means of preventing stress cracking.