Analysis of application status of pipeline coating

1 Introduction

At present, buried long-distance oil and gas pipelines are protected against corrosion by a combination of anti-corrosion coating and cathodic protection. As one of the key technologies for pipeline has been developed for more than half a century and is still a research hotspots around the world. Pipeline coating protection mainly uses anti-corrosion coatings with good insulation, penetration resistance, impact resistance and other properties to prevent the entry of moisture, oxygen and corrosive media in the surrounding environment , so as to achieve the purpose of anti-corrosion. It has experienced the application era of petroleum asphalt, epoxy coal pitch, coal tar enamel, two-layer structure polyethylene, fusion-bonded epoxy powder (FBE), and three-layer structure polyethylene (3PE). Currently, 3PE, FBE And other anti-corrosion coating tripartite situation [2]. Pipeline coating can be mainly divided into five aspects according to the application: main line pipeline coating, station pipeline coating, pipeline coating repair, pipeline coating repair, and pipeline inner coating.

2 mainline pipe coating

2.1 Current situation abroad

In foreign countries, 3PE and FBE are mainly used for trunk pipeline coating at present , among which North America generally prefers to use FBE, while Europe prefers to use 3PE. In recent years, some new :

(1) The HPCC anti-corrosion coating system was developed by Bredero Shaw of Canada. It consists of a three-layer structure of epoxy powder bottom layer, adhesive middle layer and sprayed polyolefin powder top layer. Compared with 3PE, it has a significant The advantage is that it solves the problem of cathodic protection current shielding , and the spraying technology improves the main properties such as interlayer adhesion, cathodic stripping resistance, and aging resistance.

(2) Spraying polyurea anti-corrosion coating is a newly developed anti-corrosion technology in the past 10 years. It breaks the defects caused . It has high elasticity, high hardness, good anti-corrosion and waterproof performance and Mechanical properties, but the application process is restricted by price, coating process and maintenance.

(3) There are also polyurethane, epoxy/modified polyethylene powder, inorganic non-metallic materials, nano-modified materials, composite materials, etc. [5].

Overseas trunk pipeline coating has been developed for more than half a century and is relatively mature. The external anti-corrosion coating systems specified in "NACE RP 0169 External Corrosion " include [6]: coal tar, prefabricated film (cold-wrapped tape), fusion-bonded epoxy coating, polyene

Hydrocarbon coatings and paraffins, these coating technologies also have supporting technical standards, such as NACE standards, API standards, ISO standards, CSA standards, DIN standards, etc.

2.2 Domestic Status

In CHINA, 3PE, single-layer/ double-layer FBE, polyethylene tape, coal tar enamel, petroleum asphalt, etc. are mainly used for trunk pipeline coatings. Since 2002, almost all new pipeline coatings have been 3PE.

The coating application status of trunk pipelines in CHINA is relatively good. In just a few decades , a relatively complete technical system has also been formed, such as "GB/T 21447-2008 Code for External Corrosion Control of Steel Pipelines", "GB/T 50538-2010 Technical Standards for Anticorrosion and Insulation Layer of Buried Steel Pipelines; for each

There are corresponding specifications and standards for each application coating, such as "GB/T 23257-2009 Polyethylene anti-corrosion coating for buried steel pipelines" and so on. 2.3 Production requirements

(1) The coating selection system for new pipelines is too single

At present, almost all the coatings of new domestic pipelines are made of 3PE. Although the 3PE anti-corrosion coating combines the excellent anti-corrosion and mechanical protection properties of FBE, it is not multi-functional and has its shortcomings, such as coating stripping , cathodic stripping, and cathodic protection. Shielding, peeling off anti-corrosion layer corrosion under the film, stray current interference, etc. According to the applicability of the coating to various soil types, the surrounding environment, and the actual situation on site, a scientific and complete system for the selection of coatings for new pipelines should be established. For example, 3PE is used in rockwork, water network, swamp and other areas, FBE is used in dry soil and desert areas, and pH value, ultraviolet light .

(2) 3PE pipe coating peeling failure

In recent years, the pipeline operation department has repeatedly discovered the peeling phenomenon of the 3PE anti-corrosion layer during daily maintenance. Most of the peeling forms are: the appearance of the anti-corrosion layer after the excavation , the epoxy powder layer is peeled off from the steel pipe, and there is only a small amount of powder or no powder Retained, and the surface of the steel pipe is dry and free of corrosion marks. According to reports published abroad, similar problems have also occurred in 3PE pipelines in Mexico, Saudi Arabia, Iran and other countries [7] . At present, there is a lack of targeted research on this in the world, and the cause cannot be determined, and it is limited to theoretical speculation.

(3) Compatibility of pipeline coating and cathodic protection

The pipeline coating and the cathodic protection system together form the pipeline anticorrosion system . The coating provides the first layer of protection long-distance pipelines. The current density will be affected by the performance and state of the anti-corrosion coating . That is to say, the better the insulation performance of the pipeline coating, the lower the cathodic protection current density, and the smaller the leakage area of ​​the coating that it can effectively protect. Therefore, there must be a compatibility problem between pipeline coating and cathodic protection, which needs to be further studied.

3 Station pipeline coating

3.1 Current situation abroad

In foreign countries, composite coating structures . The primer and intermediate transition coatings are epoxy or polyurethane coatings, and the outer coatings are mostly polyurethane or fluorocarbon coatings with excellent weather resistance and wear resistance. ; For buried pipelines, developed countries such as Canada and the United States use epoxy, coal tar, and polyurethane coatings [8]. Relevant standards such as "NACE RP 0190 External Protective Coatings for Connections, Fittings and Valves of Underground or Submerged Metallic Piping Systems ".

3.2 Domestic Status

In CHINA, composite anti-corrosion coatings are also used for above-ground pipelines in stations, such as acrylic polyurethane coatings, cross-linked fluorocarbon coatings and matching intermediate paints; buried pipelines in stations use prefabricated anti-corrosion coatings of the same level as trunk line coatings, Solvent-free epoxy, polyethylene (propylene) glue is used for on-site coating

Adhesive tape or its composite structure, and solvent-free epoxy glass fiber reinforced plastic, etc. [9]. Relevant standards such as "Q/SY 1186-2009 Technical Specifications for Off-site Corrosion Control of Oil and Gas Fields and Pipeline Stations".

At present, there are many problems with the coating of pipelines in domestic stations, and cases of corrosion and perforation of buried pipelines have occurred in , which has attracted great attention. The anticorrosion of buried pipelines in stations has become a weak link in pipeline anticorrosion design.

3.3 Production requirements

(1) The national or industrial standards lack the content of the station pipeline coating. The coating protection of the station pipeline is the weak , and there is no content for the station pipeline coating in the national or industrial standards. The existing enterprise standards or other relevant standards to revise and integrate the current national or industry standards to fill in the gaps in the standards and provide .

(2) Anti-corrosion of heterogeneous parts such as valves In recent years, due to factors such as materials, construction, and environment, failure cases of coatings in valve chamber equipment are common, especially coating construction and repair of buried valves and auxiliary pipelines in valve chambers and other special-shaped parts , and become a difficult problem in pipeline corrosion and protection management. Coating protection technology for heterogeneous parts such as valves should be formed as soon as possible to solve such problems.

4 Coating joints for pipes

4.1 Current situation abroad

Internationally, the same or similar coating materials as the main body of the pipeline are commonly used for joint joints. For example , epoxy powder or liquid epoxy joints are used for FBE coatings, and polyolefin heat shrinkable . At present, polyolefin heat shrinkable tape, liquid epoxy, liquid polyurethane and viscoelastic materials have become the mainstream. In recent years, some new filling materials have also appeared :

(1) Spraying polyurea elastomer material, a new type of solvent-free and pollution-free spraying material developed to meet environmental protection requirements, the biggest advantage is that it can be repaired at low temperature [10]. CHINA Petroleum Pipeline Research Institute in the Lanzhou-Yinchuan Gas Pipeline Project

The on-site application demonstration of non-toxic polyurea joint coating was carried out, and the test results were good.

（2）ATO超陶（陶瓷金属）防腐防污材料，由韩国爱涂防水防腐株式会社研发，属于无机高分子双组份涂料，依靠基本剂与固化剂混和后自身发热而逐渐固化，具备设计寿命长、水中可固化的优良特性 [10] 。

（3）聚合物网络涂层（PNC），是3M公司专为三层结构涂层管道系统开发的补口材料，含有聚烯烃和环氧树脂成分，具有极强的化学反应性能，在不使用粘结剂时，能直接应用于FBE和聚烯烃表面实现

粘结 [2] 。国外的管道涂层补口标准有《NACE RP 0303管道热收缩套现场补口、施工、性能和质量控制建议作法》、法国道达尔（TOTAL） 《GS GR COR 420 rev 04管 道 涂 层 补 口 》、英 荷 SHELL（ 壳 牌 ）《DEP31.40.30.37-Gen.线路管道涂层系统补口及修复》等。

4.2 国内现状

近几年，管道涂层补口在国内引起了广泛关注，先后引进了国外多种专业材料，技术发展较为迅速，主要的补口材料有：辐射交联聚乙烯热收缩带（套）、FBE、无溶剂环氧、液体聚氨酯、粘弹体等。现行标

准如《GB/T 50538-2010 埋地钢质管道防腐保温层技术标准》、 《GB/T 23257-2009埋地钢制管道聚乙烯防腐层》等。

4.3 生产需求

（1）积极推进新建管道涂层补口机械化作业

从陕京线开始，国内新建管道大多采用3PE结构，补口采用环氧底漆加热收缩带结构。相对3PE防腐层自动化流水线的生产方式，热收缩带补口基本为手工操作，受现场施工环境、工人安装熟练程度等因素影响很大，后期运行中发现热收缩带补口存在较为严重的质量问题，成为管道防腐层中最薄弱的环节。因此，应积极推进新建管道层补口机械化作业，以排除人工安装因素的影响。

（2）缺乏管道补口材料的长期性能评价技术

调查资料显示，往往失效的补口材料在工程应用时送检样品均满足相关标准/工程技术规范的要求，建设期间监理按要求抽检的补口质量也满足标准要求，但在运行几年后，却出现了不同程度的失效现象。补口材料在实际运行环境中的长效性是决定其使用寿命的关键指标，但相关标准/工程技术规范缺少对补口材料长期性能的评价方法和技术指标要求。因此，有必要研究管道补口材料的长期性能评价技术。

5 管道涂层修复

5.1 国外现状

国外管道涂层修复技术较为成熟，采用机械化作业，除旧防腐层、表面预处理、涂覆新涂层流水化一体进行，涂覆工艺应用较多的是沟下机械喷涂法和地面组合机具修复法。修复材料的选择也较为严格，强调适用性，常用的有煤焦油磁漆、聚乙烯胶带、液体环氧涂料、聚氨酯涂料、热收缩带等 [11] 。

5.2国内现状

目前，国内管道涂层修复技术较为落后，修复材料主要采用石油沥青、聚乙烯胶带、液态固化类涂料，涂覆工艺主要采用人工涂覆法或沟下机械缠绕法，受材料、环境、施工因素影响较大。现行标准如《SY/T 5918-2004 埋地钢制管道外防腐层修复技术规范》。

5.3 生产需求

（1）优化修复工艺、研制相应的修复机具目前，我国管道涂层修复主要采取人工涂覆或半机械化缠绕的工艺方法，施工机具较为落后，涂层修复质量难以得到保证。应积极吸收国外专业技术，优化涂层修复工艺，并研制相应的修复机具，推进管道涂层修复施工的机械化作业。

（2）埋地结露管道外防腐层修复

目前，漠大线一些低温运行管道，因输送介质温度较低，当管体表面温度低于环境露点时，管体表面会有大量水汽凝结，俗称管道“出汗”。出汗时的水汽极大影响修复涂层与管体和原防腐层间的粘接性能，容易产生剥离；并且在气候寒冷时还存在易低温脆裂、液体涂料产品无法充分固化等难题。为此，应尽快研究解决埋地结露管道的外防腐层修复难题。

6 管道内涂层

6.1 国外现状

目前，管道内涂层在欧美等管道工业发达国家已经被广泛应用，常用于管道内涂层的材料以热固性树脂粉末涂料为主，如环氧酚醛树脂及改体、液体环氧、粉末环氧、富锌、聚氨酯、聚酰胺材料等 [12] 。相

关标准如《API-RP5L2 非腐蚀性气体输送管道内涂层建议准则》，英国的COPON双组份液体环氧涂料，成功应用于世界各地的天然气干线管道内涂层。

6.2 国内现状

国内的管道内涂层应用较晚，与国外尚存在较大差距，目前主要应用在输气管道上，环氧类涂料成为国内应用较多的管道内涂层材料 [13] 。现行标准有《GB/T 23258-2009钢制管道内腐蚀控制规范》、 《SY/

T 0442-2010 钢制管道熔结环氧粉末内防腐层技术标准》等。

6.3 生产需求

目前，国内的管道内涂层主要应用在输气管道上，原油及成品油管道应用较少，应尽快对管道内涂层的材料、结构、性能、施工工艺等方面进行研究，使管道内涂层材料广泛应用于各种输送介质类型的管道。

7 总结

管道涂层是油气管道腐蚀控制的基础，从理论上讲，如果涂层完好的涂敷在管道上，成功隔绝其与周围土壤环境的接触，它将起到99%以上的保护作用，再加上阴极保护则可以实现完全保护。由此可见，管道涂层是油气管道腐蚀与防护的第一层堡垒，其重要性不言而喻。通过文章上述分析，对于管道涂层应用较成熟的方面，应通过自主研发或技术交流等方式，保持与国外技术同步，并及时修订或编制相应的规范标准，形成完善的技术体系；对于应用尚未成熟的方面，应积极借鉴、引进、消化、吸收国外专业技术，并通过工程实践检验应用成果；对于本文所提出的生产需求，建议国内相关科研院所立项研究，尽快解决这些生产实际中的现实问题。

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