Ⅰ. Understand the characteristics and common problems of large galvanized steel pipes
Large galvanized steel pipe is usually used for industrial water, gas, sewage, and municipal engineering, with diameters ranging from several hundred millimeters to several meters. The galvanized layer mainly protects the steel pipe from environmental corrosion, but in long-term service, the following will occur:
Zinc layer damage and local corrosion (especially in humid, acidic, and alkaline environments or joints)
Pipe body corrosion causes thinning of the pipe wall and reduces the pressure-bearing capacity
Inner wall scaling, scale, and corrosion product accumulation affect flow and pipeline life
According to the “Steel Pipe Anti-Corrosion Design Code”(GB/T 2423-2008) and NACE standards (such as NACE SP0169), the transformation of old large galvanized pipes requires the combination of anti-corrosion engineering, structural testing, and material selection, and cannot simply rely on cleaning or local repair.
Ⅱ. Steps and technical points for the transformation of large galvanized steel pipes
1. Structural and corrosion status detection
Use an ultrasonic thickness gauge (UT) to detect the actual thickness of the pipe wall and determine the degree of corrosion
Use X-ray or magnetic particle inspection to check welds and weak areas
The inner wall can be mechanically cleaned (pigging) with video inspection to confirm corrosion and scaling
2. Surface treatment and corrosion control
When large areas are corroded, use sandblasting or shot blasting to remove rust, remove the rust layer and residual galvanized layer, and ensure that the substrate is exposed and clean
Use rust converter to treat local rusted areas to stabilize rust and prevent further spread
High-performance anti-corrosion primer (such as epoxy zinc-rich primer) can be sprayed on key parts
3. Inner wall treatment
After pigging, use inner wall epoxy coating or lining technology (such as epoxy resin lining, polyethylene lining) to prevent water corrosion, improve corrosion resistance, and extend pipeline life
Mechanical cleaning or chemical descaling of areas with severe scaling
4. Welding and reinforcement
Repair welding can be used to reinforce the seriously corroded parts. If necessary, install pipe reinforcement rings or replace pipe sections
Ensure non-destructive testing (NDT) after welding to ensure quality
5. Re-galvanizing (depending on the specific situation)
For specific pipe sections, hot-dip galvanizing can be used to restore anti-corrosion protection
Or use cold-sprayed zinc coating as a quick on-site protection method
6. Structural protection and environmental control
Add a protective layer to the outside of the pipeline (such as anti-corrosion tape, asphalt paint, or polyethylene casing)
Reasonably arrange drainage and cathodic protection systems to prevent electrochemical corrosion
Ⅲ. Engineering specifications and safety standards
Follow API 570 (Pipeline Inspection and Maintenance Standard)
Implement NACE MR0175/ISO 15156 (Anti-corrosion Material Standard)
Reference GB 50236-2011 “Steel Structure Anti-corrosion Engineering Construction and Acceptance Code”
Use certified materials and coatings to ensure pressure resistance, temperature resistance, and anti-corrosion performance
Ⅳ. Summary of renovation suggestions
- ①Renovation stage: Main operation content
- ②On-site inspection: Ultrasonic thickness measurement, flaw detection, video inspection
- ③Surface treatment: Sandblasting, rust removal, rust conversion, primer spraying
- ④Inner wall protection: Epoxy coating, cleaning of scale
- ⑤Structural reinforcement: welding reinforcement, and pipe section replacement
- ⑥Anti-corrosion reprocessing: hot-dip galvanizing or cold zinc spraying
- ⑦Environmental protection: external anti-corrosion layer, cathodic protection
V. Topregal product and service support
As a professional steel product manufacturer, Topregal is committed to providing high-quality steel pipe tubing, steel sheets, galvanized steel coil, and anti-corrosion solutions for large industrial and municipal pipeline systems. The products comply with many international certification standards, such as ASTM, ISO, and UL, have high compressive strength, and are combined with professional anti-corrosion technology to ensure the safety and efficiency of large-scale galvanized steel pipe renovation projects. We provide one-stop technical support, covering testing, design, and construction plan recommendations to help extend the life and upgrade of pipeline systems.
Have any other questions? Welcome to contact us, we will serve you wholeheartedly!
