Feng Shaoguang: Surface treatment is the "conscience" of pipeline anticorrosion construction

Feng Shaoguang
China Petroleum Pipeline Science and Technology Research Center
Director of The Institute of Experimental Testing Technology
❖ Media Interview
"Coating and Protection" E Zhongmin
Feng Shaoguang, Director of the Experimental Testing Technology Institute of the China Petroleum Pipeline Science and Technology Research Center, Senior Engineer, Ph.D. Pipeline anti-corrosion coating technical experts, national certification and accreditation of third-party testing laboratory head, national assessment committee (CMA), national anti-corrosion standardization technical committee (SAC/TC381) member, "oil and gas storage and transportation" magazine youth editorial board. Has been responsible for the oil pipeline "3PE pipeline anti-corrosion layer stripping process and countermeasures research," "3PE pipeline anti-corrosion coating failure analysis and quality control", the Group's "13th Five-Year Standard Research" and other projects

. He has won the second prize of scientific and technological progress of PetroChina Corporation, the third prize and the third prize of scientific and technological progress of Hebei Province and other provincial and ministerial awards.
has been responsible for or participated in the preparation of 3 NACE international standards, 1 national standard and 12 industry standards, and is the Chair of the WORKING Group on NACETG520 and TG555. The first author published 10 papers, including 2 NACE papers. At present, mainly engaged in anti-corrosion coating third-party testing and evaluation, defect repair and pipeline testing and other fields of testing, research and standardization work, has a wealth of laboratory and field practical experience.
are the factors that cause pipe corrosion? What are the main protection methods?
, The transportation of China's oil and natural gas resources mainly depends on pipelines to achieve, pipes are generally steel spiral welding pipes. Due to the complex terrain of the pipeline crossing, the external environment is not only different in space, but also changes with time, and will be subject to the erosion of various media. Overhead pipes are susceptible to atmospheric corrosion, while buried or underwater pipes are subject to soil corrosion, bacterial corrosion and stray current corrosion. In addition, pipeline transmission media also lead to pipelines facing severe internal corrosion environment, such as the transport of natural gas containing H2S, CO2 and water, the transport of crude oil containing S and O2. According to the relevant data research statistics, the average corrosion rate of underground pipes is more than 1.5mm/a. It is not uncommon for corrosion perforation to occur after the underground oil and gas pipeline in China is put into operation from 1 to 2a. Corrosion is a key factor affecting the reliability and service life of pipeline system, and failure will lead to huge economic losses, major disaster accidents and threats to public safety.
effective measures can be taken to reduce the chance of corrosion and reduce the degree of corrosion. At present, the main anti-corrosion measures of pipelines are "anti-corrosion coating" and "cathode protection". Typically, an off-pipe corrosion system consists of an anti-corrosion coating and cathode protection. The combination of cathode protection current and anti-corrosion coating allows for the construction of a superior and cost-effective corrosion protection system. Anti-corrosion coatings are used to protect most metal surfaces, while cathode protection systems are designed to protect areas where the integrity of the anti-corrosion coating is compromised.pipeline laying construction site
anti-corrosion coating as the main means of pipeline corrosion protection, new pipeline coating selection and design should be considered? How to view the price of raw materials?
anti-corrosion coating is an important part of the anti-corrosion technology measures of buried oil and gas pipelines, and it is the barrier between the pipeline and the external corrosive environment, which can effectively cover more than 99% of the surface of the pipeline. As part of an anti-corrosion system, coatings can reduce the total yin-preserving electrical flow required to protect pipes by reducing the path (contact) between metals and electrolytes. In addition, the coating allows for a more uniform distribution of the cathode current and for rapid polarization.
a number of factors need to be taken into account in the selection of anti-corrosion coatings, and cost is just one of them. According to a foreign research report, in the pipeline project costs, construction installation accounted for 67%, management accounted for 3%, materials accounted for 30%. Steel pipes account for 85 per cent of "material" costs, coatings for 10 per cent and others for 5 per cent. The cost of the coating system also includes raw materials, coating construction, coating repair, and filling of ring welds. Overall, pipe coatings account for only 4% of the cost of pipes that have been laid and installed, and other costs include pipeline construction work belts (survey, clearance, damage recovery), engineering/testing, tax/transportation, materials other than anti-corrosion coatings, labor, and others (laws, regulations). Anti-corrosion coatings are critical to pipe life, and the longer the pipe life, the lower the relative cost. The raw material cost of anticorrosive coatings is only a fairly small part of the pipeline cost.
in addition
, when selecting anti-corrosion coating, construction and installation needs to consider the anti-mechanical damage performance of the coating, the terrain along the pipeline, backfilling soil, soil condition, the ring weld recillation scheme, the application work needs to consider logistics and quality assurance, the pipe service life needs to take into account the coating resistance stability, non-yin shielding, pipe operating temperature, soil conditions - resistance to soil chemical properties and soil stress, stress cracking, life cycle costs, etc.
there are many reasons to choose a particular anti-corrosion coating, among which the compatibility of the anti-corrosion coating with the cathode protection system is very important. Anticorrosive coatings require a high resistance and should be able to maintain such a high resistance over pipe life. If the anti-corrosion coating fails, the anti-corrosion coating must never shield the cathode protection current and must not prevent the protective current from reaching the piped steel surface. There are many factors that ensure resistance stability, which minimizes the demand for cathode protection currents. Among these factors are the quality of the coating of the main channel coating and the effectiveness of the compatible ring weld re-port coating. In addition, anti-corrosion coatings should not create an environment that causes steel stress corrosion cracking (SCC).
coating as an input, life-long benefit of anti-corrosion form, is to ensure that the pipeline is resistant to external corrosion, long-term safe and reliable operation of the key. However, due to the concealment and lag of pipeline corrosion, the construction is often not given sufficient attention at the beginning, resulting in frequent coating failure and resulting safety accidents after several or ten years of pipeline operation. Pipe construction and coating applied irrevertability, then regret the original, it is too late!
the coating process and quality of the pipe epoxy powder controlled?
although the application of the fused epoxy powder (FBE) pipe coating is a simple sequential step. However, the final effect of any coating process will depend on the attention and control of the coating details. The entire application process mainly includes the following processes: (1) tube inspection, (2) blast cleaning (surface pre-treatment, possibly including pickle or other treatment) ;(3) steel pipe heating, (4) powder spraying, (5) curing, (6) cooling, (7) coating inspection and (8) repair.
, the quality problems in the application process of FBE coating are mainly concentrated in raw material quality and surface treatment.
raw materials, low-cost competition has always been the key to affect the quality of anti-corrosion coatings. In order to reduce costs, some enterprises may add recycled powder, recycled materials or increase the proportion of fillers, which greatly affects the quality and quality of products. In view of these problems, it is suggested to strengthen and perfect the bidding mechanism, product quality sampling system (such as random sampling, witness sampling, etc.) and batch quality control.
surface treatment is the most critical link affecting the performance of the coating, but also the "conscience work" of pipe coating.
for many coating systems, especially those that require higher and higher requirements, the surface of the steel pipe needs to be treated according to different process requirements. For blast cleaning, understand the grade and hardness of the steel pipe, select the type and particle size distribution of the steel ball/sand mixture accordingly, and properly control and manage the abrasive mixing ratio and cleanliness. Acid washing can effectively remove contaminants, especially chlorides, from the steel surface after blast cleaning. Chromate treatment further optimizes coating performance to ensure overall consistency in coating quality, but environmental issues limit its use. In addition, the material equipment used in pipe coating plant operations, as well as the atmospheric environment, can also affect the quality and performance of the coating. Good surface treatment will bring long-term benefits. However, if the pipe surface treatment is not done well, it can have a great impact on the service life of the coating, which can be costly.
the coating protection system should be selected for different plumbing conditions?
present, the anti-corrosion outside the oil and gas pipeline mainly uses three-layer structure polyethylene anti-corrosion layer (3PE), it is FBE as the bottom layer, polyethylene adhesive as the middle layer, polyethylene (PE) as the outer layer of anti-corrosion structure. FBE has good antioxidant osmosis and anti-corrosion properties, PE has good waterproofness, but also good mechanical strength, can resist mechanical damage in transportation and construction. At present, the structure has become the mainstream mode of anti-corrosion coating of domestic pipelines.
In addition, there are some pipelines in China using single-layer FBE or double-layer FBE for external corrosion protection, although the anti-corrosion structure is the most commonly used coating in North America, but due to construction and other factors, the proportion of application is not high. Various terrains and soils have different performance requirements for corrosion-resistant coatings, large undulating terrain requires coatings to meet the requirements of cold bending on site, stone square areas require good impact resistance of the coating, clay areas require coating resistance to soil stress, salinized soil requires coating materials resistant to chemical media immersion.
human conditions are also factors that coating selectors should pay sufficient attention to. The so-called humanistic condition refers to the quality consciousness of the construction unit and the quality of the residents of the area through which the pipeline is passed. The phenomenon of brutal loading and unloading and brutal construction has not been eliminated in our country; A project should not choose a variety of anti-corrosion layer, should be based on the worst conditions to choose one or two anti-corrosion layer. It seems like some waste, in fact, taking into account pipe inverted, cloth pipe and other factors, the fewer varieties may be more provincial investment, which is closely related to the setting of domestic anti-corrosion plant, in the pipe factory prefabribrial anti-corrosion layer will save a considerable amount of pipe reverse freight.
pipeline operation results in FBE coating scratching
oil and gas pipeline coating, currently mainly using FBE or solvent-free liquid epoxy coating for corrosion protection. Solvent-based or solvent-free internal resistance reduction coatings are commonly used for large diameter gas pipelines. Pipeline is also the focus of the field of pipe corrosion, there are a large number of water conservancy projects are under construction or planning, the main form of corrosion protection is internal FBE coating, external polyethylene powder coating or 3PE coating. There are also sewage pipes, drinking water pipes, such as the use of internal and external FBE, internal and external solvent-free epoxy coating or internal and external solvent-free polyurethane coating anti-corrosion form.
With the opening of key cross-sea bridge projects such as Hangzhou Bay Bridge and Hong Kong-Zhuhai-Macao Bridge, there are more and more applications of steel pipe piles in the field of cross-sea bridges, and steel pipe piles have the characteristics of large diameter, long length and large quality. At present, pipe piles mainly use single-layer, double-layer and three-layer FBE anti-corrosion form, when the need for internal wall corrosion protection, usually using solvent-free liquid epoxy coating. In addition, in order to reduce the mechanical damage caused to the pipe pile during the bridge laying process, an attempt is also being made to add the structural form of the composite outer layer in the pipe pile splash area.
thermal pipe is mainly using foaming polyurethane insulation layer and polyethylene outer layer insulation structure. When pipe corrosion protection needs to be considered, the steel pipe needs to be coated with an anti-corrosion layer first, usually with an FBE coating.
are the main problems in the service of the anti-corrosion coating of the 3PE pipeline? What are the possible causes of these problems?
China since the 1990s, Shaanxi-Beijing gas pipeline for the first time using 3PE coating so far, the West-East gas transmission project 1/2 line, China and Myanmar, China and Russia, Qing Tie, Lan Zheng Chang, Shi Ninglan and many other national key pipeline projects have adopted 3PE coating, 3PE has become China's pipeline anti-corrosion leading coating. But in the past 10a, there have been several cases of failure of 3PE coating bonding on land long pipelines abroad, including in India, South America, Iran, Syria and Gabon, all of which have reported large-scale stripping between the FBE bottom and the steel pipe substrate. Domestically, on-site investigation of the effectiveness of the anti-corrosion layer also found a large area of 3PE anti-corrosion layer bonding failure phenomenon, and the anti-corrosion layer after stripping failure will shield the cathode protection current. When water vapor enters the interface between the stripping coating and the steel pipe, the pipe body will corrode freely, burying a hidden danger for the safe operation of the pipe.
3PE anti-corrosion coating bonding failure
From the failure of domestic and foreign 3PE pipeline, the current corrosion layer failure mainly has the following characteristics:
(1) stripping mainly occurs between FBE and tube body, anti-corrosion layer and tube body adhesion basic loss, with a knife to cut the corrosion layer, the free hand can be the overall peeling of anti-corrosion layer, stripped after the surface of the tube basic non-oxide powder residue, there are Metallic luster, non-corrosive, some pipe surface has dirt or impurities visible to the naked eye; (2) many pipe corrosion layer failure occurred after production 3 to 5a, or even just put into production, there is corrosion layer stripping failure, far below the pipe design life of 30 to 50a requirements; (3) corrosion layer failure range, different conveyor processes, different climate areas and different pipe diameter pipes have corrosion layer bonding failure problems occur.
, 3PE anti-corrosion layer failure, especially the early overall stripping failure, has become the main problem facing the domestic 3PE pipeline. In response to this problem, domestic and foreign have also carried out relevant research work, based on the completed relevant research results, it is believed that the causes of early bonding failure of 3PE anti-corrosion layer mainly include:
(1) surface treatment;
the defects of the anti-corrosion layer and the resulting coating failure is a serious quality problem, which affects the quality of the product and causes the corrosion layer and even the pipe to be scrapped. Some coating defects can be checked out of the pipe post, some in the pipe site can be found, some to the pipeline construction site to expose the problem, some pipe service can only be found. However, once a problem arises, it is not only extremely difficult to repair, but also difficult to guard against because the risks posed may take a considerable amount of time to be exposed. Therefore, the quality of coating must be prevented and solved in the production process.
the application of FBE system in the field of pipeline corrosion prevention is increasing gradually, but also often the problem of coating failure, what are the main forms of failure? Where can I improve?
many properties change as the coating ages. Most performance changes often depend on the external environment in which the pipeline serves. stand real.