First, Corrosion Protection Classification of Spiral Steel Pipe
Spiral steel pipe corrosion protection treatments are mainly divided into two categories: external wall corrosion protection and internal wall corrosion protection. Different combinations are usually selected depending on the conveying medium and the operating environment.
(I) External Wall Corrosion Protection Technology for Spiral Steel Pipe
This is the focus of spiral steel pipe corrosion protection, as the external wall is exposed to a complex corrosive environment such as soil, moisture, microorganisms, and stray currents.
1. Polyethylene Three-Layer Corrosion Protection (3PE)
·Structure: Consists of three layers. The first layer is fusion bonded epoxy (FBE), the second layer is adhesive, and the third layer is extruded polyethylene (PE).
·Features: This is one of the most commonly used and highest-performing corrosion protection methods internationally. It combines the high adhesion and cathodic disbonding resistance of FBE with the excellent mechanical protection, impact resistance, and superior water vapor permeability of polyethylene.
·Standard: Widely used in long-distance oil and natural gas pipelines. 2. Epoxy Coal Tar Enamel
· Structure: Typically uses a glass cloth-reinforced epoxy coal tar coating. Common grades include standard, reinforced, and extra-reinforced.
· Features: Low cost, mature technology, and excellent water and chemical resistance. However, it is brittle, has poor impact damage resistance, and is environmentally friendly (due to the presence of coal tar). Its use has gradually decreased in recent years.
· Standard: Historically, it was commonly used for municipal water supply and gas pipelines, as well as for pipelines crossing waterways, swamps, and other highly corrosive areas.
3. Epoxy Powder (Fusion Bonded Epoxy, FBE)
· Structure: A single layer of epoxy powder is electrostatically sprayed and fused to the steel pipe surface at high temperature, forming a hard film.
· Features: Excellent adhesion, good chemical resistance, and high temperature resistance. Disadvantages include a thin coating and weak mechanical damage resistance. It serves as a base layer for 3PE, but can also be used alone.
· Standard: Commonly used for corrosion protection of oilfield gathering and transportation pipelines, hot water pipelines, and pipe fittings. 4. Polypropylene Three-Layer Corrosion Protection (3PP)
·Structure: Similar to 3PE, but the outermost layer uses polypropylene (PP).
·Features: High-temperature resistance (up to 125°C) is superior to 3PE (approximately 80°C), while other properties are comparable to 3PE. It is primarily used for conveying high-temperature media, such as thermal crude oil and high-temperature hot water.
5. Polyethylene Two-Layer Corrosion Protection (2PE)
·Structure: The FBE layer is omitted, leaving only the adhesive and polyethylene layers.
·Features: Corrosion resistance is superior to single-layer PE, but adhesion and cathodic disbondment resistance are inferior to 3PE. It is lower in cost and can be used in applications with slightly lower requirements.
(II) Inner Wall Corrosion Protection Technology for Spiral Steel Pipe
Mainly designed to prevent corrosion and scaling of the conveying medium on the inner wall of the steel pipe, thereby reducing conveying resistance.
1. Epoxy Resin Internal Corrosion Protection
·Common Types: Liquid epoxy coating, solvent-free epoxy coating, etc.
·Features: Smooth coating, reduces resistance, prevents scaling, and is resistant to corrosion from a variety of chemical media. Choose different types of food-grade or anti-corrosion epoxy coatings depending on the media (e.g., sewage, drinking water, crude oil).
· Standard: Drinking water pipes must use non-toxic coatings and obtain a health permit.
2. Cement Mortar Lining
· Features: Low cost, excellent durability, effective anti-scaling, and no water pollution. Commonly used for large-diameter water pipelines (municipal water supply and drainage).
· Disadvantages: Not resistant to strong acidic and alkaline media, and has poor impact resistance.
3. IPN8710 Polymer Anti-Corrosion Coating
· Features: A non-toxic coating with an interpenetrating network structure suitable for drinking water pipes. Resistant to acids, alkalis, salts, oils, and other media, it offers excellent overall performance.
(III) Auxiliary Protection for Spiral Steel Pipe: Cathodic Protection
No matter how good a coating is, defects (pinholes) can exist. Therefore, anti-corrosion coatings are often used in conjunction with cathodic protection to form a complete protection system. Sacrificial Anode Method: A more active metal (such as a magnesium alloy or zinc alloy) is connected to the steel pipe, causing it to become the anode in the corrosion cell and be consumed, thereby protecting the steel pipe (cathode).
Forced Current Method: An external DC power supply and auxiliary anode are used to apply a protective current to the steel pipe, causing it to become the cathode and thus be protected.
Application: This is a mandatory standard configuration for long-distance pipelines and submarine pipelines.
Second, Implementation Standards for Spiral Steel Pipe
Strict standards exist both domestically and internationally for different types of corrosion protection. Corrosion Protection Type: Chinese Standard (GB/SY), International Standard (Common), Application Area
3PE/2PE GB/T 23257-2017 DIN 30670, CAN/CSA-Z245.21 Long-distance oil and gas pipelines
FBE SY/T 0315-2013 CAN/CSA-Z245.20, AWWA C213 Gathering pipelines, municipal pipelines, and fittings
Epoxy coal tar SY/T 0447-2014 – Early-stage pipelines, underwater pipelines, and patching
3PP SY/T 0315-2013 DIN 30678 High-temperature transmission pipelines
Liquid epoxy internal corrosion protection SY/T 0457-2010 AWWA C210 Internal walls of water and oil pipelines
Cement mortar lining GB/T 50393-2017 AWWA C205 Large-diameter municipal water pipelines
Third, Summary of Standard Uses for Spiral Steel Pipes
Depending on the specific project requirements, the corrosion protection options for spiral steel pipes are as follows:
1. Long-distance oil and gas pipelines:
· Preferred: 3PE outer wall corrosion protection with cathodic protection. This is the global mainstream standard, offering an exceptionally long design life (up to 50 years or more).
· For high-temperature media: Choose 3PP outer wall corrosion protection.
2. Municipal water supply pipelines:
· Inner wall: Must use non-toxic epoxy coating or cement mortar lining to ensure drinking water safety.
· Outer wall: Depending on the soil corrosivity, FBE, 3PE, or epoxy coal tar can be selected, supplemented with cathodic protection.
3. Municipal drainage and sewage treatment pipelines:
· Inner wall: Use epoxy coal tar or corrosion-resistant epoxy coating to resist corrosive gases such as hydrogen sulfide.
· Outer wall: Reinforced epoxy coal tar or FBE. 4. Industrial pipelines for chemicals, power, and energy:
· Select the most appropriate internal anti-corrosion coating (such as FBE, specialty epoxy, etc.) based on the specific chemical composition, temperature, and pressure of the transported medium.
· External coatings are typically made of FBE or 3PE.
5. Spiral pipe for piles and foundation structures:
· Corrosion protection requirements are lower than for transport pipes. Typically, epoxy coal tar or a simple epoxy zinc-rich primer is used, primarily to prevent soil and atmospheric corrosion.
In summary, corrosion protection for spiral steel pipe is a systematic project. Based on four key factors: medium characteristics, soil/environmental corrosivity, design life, and cost budget, and in conjunction with domestic and international standards, a comprehensive approach to external and internal corrosion protection, as well as the need for cathodic protection, must be carefully selected. 3PE, due to its superior comprehensive performance, has become the gold standard for external corrosion protection for long-distance oil and gas pipelines.
Post time: Sep-02-2025