Anti-corrosion Technology of Oil and Gas Pipeline's Flanges and Bolts (Part Three)

1.6 Viscoelastic anti-corrosion systems
The viscoelastic body is mainly an anti-corrosion product developed by the Dutch company STOPAQ. It is a polyolefin-based flexible heavy-duty anti-corrosion material with a single-molecule non-bonded structure. This single-molecule non-bonded structural feature makes the viscoelastic body not only have solid characteristics similar to polyethylene (PE) but also the unique cold flow characteristics of a liquid, which can automatically infiltrate any tiny hole on the surface of the metal to be protected. It blocks the penetration and erosion of corrosive media such as moisture, microorganisms, etc. At the same time, it is wrapped with a tape made of viscoelastic anticorrosive material, and covered with an outer protective layer with excellent weather resistance and elasticity to ensure effective sealing and double corrosion prevention. DY-1 series bolt caps made of anti-ultraviolet and anti-aging polypropylene plastic are adopted for the bolts outside the flange end face to ensure complete sealing and reliability of the protected metal. The viscoelastic anti-corrosion system has low requirements for surface treatment of metal and does not require sandblasting and rust removal, which can be directly applied to the anti-corrosion of the connecting ends of various oil and gas storage and transportation equipment. Through the engineering practice and application of some pipelines and pipe fittings such as the Dutch National Gas Company, Saudi Arabian Oil Company and West-East Gas Pipeline, the results show that the viscoelastic material can remain non-curing and has excellent bonding features, reliable sealing, cathodic disbondment resistance and easy operation on site, which can effectively prevent metal from being corroded, obtaining good economic and social benefits. The reason for that is the characteristics of viscoelastic bodies, which are as follows:
(1) Excellent cold flow characteristics: The viscoelastic body has both solid and liquid characteristics. It shows good curing characteristics when there are no tiny holes on the surface of the material or it is not damaged by corrosion, but it has unique fluidity at special moments.
(2) Unique self-healing characteristics: The protected metal material is eroded and damaged or the viscoelastic body is uneven in the filling process, resulting in unbalanced forces between the molecules. The viscoelastic body around the defect will automatically flow to the damaged point or holes for self-repair, filling the entire space to prevent the metal from being further corroded, and avoid pitting corrosion in the pipeline or equipment.
(3) Excellent adhesion and sealing: Because the viscoelastic body has the same excellent adhesion with polyethylene, after the viscoelastic tape is peeled off, the viscoelastic tape on the tape can still be attached to the metal surface, maintaining a long-lasting anti-corrosion effect.
(4) A wide range of applications: It can be directly applied to carbon steel, cast iron and other metals or where PE, PP, epoxy and other coatings are coated on the metal.
(5) Good operability on-site: It is mainly manifested in the following: ①The quality is easy to control in the construction process, and it is less affected by external factors such as the environment and the personnel's operating skills. ②No auxiliary equipment is required to assist in the construction, and it is suitable for any confined and narrow space and the anti-corrosion construction of equipment of any shape. ③There are low requirements for the protected metal, and sandblasting is not required, which is easy to implement on site. ④It has good chemical resistance, and is suitable for acid-base environments with pH2 to 12. ⑤It has a wide applicable temperature range. It can still maintain excellent anti-corrosion properties in a temperature environment of -45 to 95°C. ⑥It has excellent cathodic disbondment performance. ⑦It has low storage requirements, and storage can be at room temperatures. ⑧The materials are environmentally friendly and can be cut arbitrarily with zero loss during use.
 
2. Conclusion
Through the introduction and analysis of the above six kinds of anti-corrosion technologies of flanges and bolts, it can be seen that each anti-corrosion system is different from the other in the principle, process, and application effect. Therefore, when selecting a suitable anti-corrosion system for flanges and bolts of oil and gas pipelines, the following aspects should be comprehensively considered:
(1) Environmental factors
The differences in climate between regions, environmental factors such as salinity, humidity, sunshine, temperatures and ground temperatures can affect the application effect of the anti-corrosion system. Therefore, environmental factors play an important role in the reasonable selection of anti-corrosion systems.
(2) Cost expenditure

The cost of the anti-corrosion system is different due to different construction procedures and different anti-corrosion materials used for the six anti-corrosion systems. For now, the cost of the viscoelastic anticorrosion system and Enviropeel anti-corrosion is significantly higher than the other four anticorrosion systems.
(3) Anti-corrosion effect

The requirements for anti-corrosion effects are different due to the different business operations of each user. Generally speaking, the greater the risk factor of the medium transported in the pipeline is, the greater the corrosion of flanges and bolts becomes after the change of the physical and chemical properties. Therefore, when choosing an anti-corrosion solution, an anti-corrosion system with a better anti-corrosion effect is preferred.
(4) Service lives

The user has certain requirements for the one-time service life of the anti-corrosion system due to the different anti-corrosion materials and applicable environment of each anti-corrosion system. Buried oil and gas pipelines and their parts are buried underground for a long time. If the anti-corrosion system has a short service life, it will be necessary to excavate multiple times to replace anti-corrosion materials, resulting in increased costs. The viscoelastic body can remain non-curing, and effectively prevent corrosion for nearly ten years, which has a service life that is significantly longer than the other five anti-corrosion systems.
(5) Post-maintenance

There will be a certain degree of failure for the anti corrosion system due to the impact of the anti-corrosion system in severe extreme weather and occasional accidents. Common failures include peeling off of the paint, melt dripping, and peeling of the protective tape. When these failures occur, they will increase the workload and cost of subsequent maintenance. The viscoelastic anti-corrosion system has unique self-repair characteristics, and its later maintenance is easier than the other five anti-corrosion systems. In recent years, many Chinese anti-corrosion material companies have gradually had a breakthrough the technical barriers of viscoelastic bodies, and have developed and produced products with better performance than foreign countries, making up for the gap in the domestic market. With the continuous research in the field of viscoelastic anticorrosive materials in China, their cost performance will continue to increase, providing enterprises and institutions with more and better choices in the anti-corrosion technology of flanges and bolts of oil and gas pipelines.