Spiral welded steel pipes for offshore structures require comprehensive electrochemical corrosion protection solutions. Discover E.NHAT’s material technology, coatings, cathodic protection and typical seaport projects.

What is spiral welded steel pipe (SSAW)?

Spiral Welded Steel Pipe (SSAW) is a type of pipe manufactured by rolling steel strip (usually hot rolled steel coil) in a spiral shape and welding along that spiral by submerged arc welding (SAW) from both the inside and outside.

Marine structures—from ports and breakwaters to seawater pipelines—are exposed to harsh environments: salt, high humidity, temperature fluctuations, and natural currents. In this context, spiral welded steel pipes or alloy steel pipes play an essential role, requiring technical solutions to prevent electrochemical corrosion, ensuring the longevity and safety of the structure.

This article will analyze in detail:

1. The challenge of electrochemical corrosion in marine environments
2. Selection of materials and welding technology in the production of spiral welded steel pipes for offshore construction
3. Coating and cathodic protection solutions for offshore spiral welded steel pipes
4. Design, construction and maintenance of spiral welded steel pipes in offshore construction
5. Typical marine construction projects of E.NHAT Group

1. The challenge of electrochemical corrosion in marine environments

1.1. Reasons

The marine environment is one of the harshest environments for metal materials, especially steel. Electrochemical corrosion not only occurs quickly but is also difficult to control without appropriate technical solutions. Here are three main causes leading to this situation:

• The impact of chloride ions (Cl⁻) in seawater: Cl⁻ ions easily penetrate the natural protective oxide layer on the metal surface (especially stainless steel and steel), creating structural breakdown points, forming small pitting corrosion. Over time, pitting develops into salt mine cracks.

• The potential difference between the metallic areas and the inert areas on the pipe surface (the phenomenon of “galvanic batteries”, leading to a “sacrificial” area (losing electrons) and corroding more quickly.

• Natural currents in seawater (or leakage currents from nearby electrical equipment) can amplify the oxidation-reduction process occurring on the steel pipe surface. Especially in shallow seawater areas where there are many electrical equipment, mooring systems or ships passing by frequently, the induced current can accelerate the corrosion rate many times if there is no suitable cathodic protection.

1.2. Consequence

• Reduces the thickness of steel pipe wall, reduces pressure resistance, especially dangerous in systems that transport seawater, wastewater or chemicals at high pressure..

Simulation image of the consequences of electrochemical corrosion:

• Pitting and cracking of welds, leading to leakage or structural destruction. Especially if the welds are underground or submerged, detection and repair are extremely difficult and costly

• Increased repair and replacement costs and disruption of construction operations, affecting auxiliary systems such as water treatment, saltwater filtration, or the entire logistics chain in the seaport.

2. Selection of materials and welding technology in the production of spiral welded steel pipes for offshore construction

2.1. Corrosion resistant materials

• Hot-dip galvanized alloy steel (3LPE/3LPP): This is a popular choice in the manufacture of spiral welded steel pipes for offshore construction thanks to the protective layer of zinc, epoxy, polyolefin.

• Duplex stainless steel (2205, 2507): Often specified for important pipes, high cost but long life.

• Aluminum-silicon coated steel: A new material in the spiral welded steel pipe industry, high corrosion resistance aluminum alloy coating

2.2. Welding and testing technology

• Submerged arc welding (SAW): for spiral welded steel pipes, ensuring deep penetration and few defects.

• Using special alloy welding rods and welding wires (containing Cr, Ni, Mo) to prevent corrosion of the weld.

• Non-destructive testing (NDT): UT (ultrasonic), RT (X-ray) to detect potential cracks. This inspection is especially important for spiral welded steel pipes used for offshore pile structures, to ensure safety and structural longevity.

3. Coating and cathodic protection solutions for offshore spiral welded steel pipes

To combat corrosion from the marine environment, spiral welded steel pipes need to be surface treated and electrochemically protected from the start. The two main lines of defense are:

3.1. Basic Coating

• 2-component epoxy paint: good adhesion, heat resistance, chemical resistance.
• Bitumen/polyurethane (PU) paint: increased elasticity, impact resistance.
• 3-layer system 3LPE/3LPP: is an international standard coating for spiral welded steel pipes underground or in continuous contact with seawater, combining hot-dip galvanized + epoxy + polyolefin, comprehensive protection.

3.2. Cathodic protection (CP)

• Galvanic anode CP: attach magnesium or zinc anode along the pipe, current flows from anode to steel.

• Impressed Current CP: use DC power supply, allow to adjust protection current.

• Design anode distance and flow rate based on seawater conductivity, pH and temperature.

4. Design, construction and maintenance of spiral welded steel pipes in offshore construction

4.1. Marine steel pipe design

• The selected wall thickness is in excess of the expected corrosion (usually plus 1–2mm).

• Diameter and length: calculated according to flow and pressure, optimizing the reduction of welds in deep water areas. E.NHAT is capable of producing large diameter spiral welded steel pipes from Ø410 mm to Ø4000 mm, optimized for water, mud, waste, or seawater supply and drainage pipes in seaports and power plants.

4.2. Construction and installation

• Depending on the terrain and purpose of use, spiral welded steel pipes can be buried underground, mounted on wharf piers, or placed afloat with a fixed anchor system.

• Underwater welding: special welding tools, heat control to avoid damaging the coating.

• External reinforcement and protection of pipes: For pipes in direct contact with ships or moving equipment, it is necessary to cover them with an additional layer of casing to protect against impact, while maintaining the effectiveness of the anti-corrosion coating inside.

4.3. Regular maintenance

• CP test: measure anode voltage, current efficiency.

• Coating test: use ultrasonic thickness, detect corrosion area.

• Replace anode when the sacrificial mass is reduced below 50%

5. Typical marine construction projects of E.NHAT Group

Project	Pipe Type / Application
International Port – Hòn Gai – Quảng Ninh	Steel pipe piles – Spiral welding
Vân Phong – Khánh Hòa Port	Ship repair pipe piles – salt resistant, high load
Hoa Phat – Dung Quat Port (Port No. 1–12)	Steel piles for logistics and large ships
Marine works of Coast Guard Command Region 1	36m long pile pipe – high pressure and salinity resistance

➤ E.NHAT’s ability and practical experience:

• Producing D800 piles up to 36m long, proving the ability to process large sizes for offshore projects.

• Applying international standards JIS, SPP, TCVN, meeting strict requirements on anti-salt corrosion.

• Implementing many packages in Hon Gai, Van Phong, Dung Quat – demonstrating experience in field implementation and serving complex seaports.

CONCLUSION

Offshore steel pipes face severe electrochemical corrosion challenges. By selecting the right materials, applying advanced welding technology, multilayer coatings and properly engineered cathodic protection, you can ensure the longevity and performance of your system.

E.NHẤT GROUP – With experience in implementing large marine projects, port piles and marine pipeline systems – always ready to advise on optimal solutions, from design, production to maintenance.