Compared to ordinary steel pipes, seamless steel pipes can withstand higher pressures. Therefore, seamless steel pipes are used in industrial production where pipelines need to withstand high pressure. Some call them the “micro-vessels of industry,” as they are indispensable in manufacturing airplanes, ships, trains, and transporting oil, gas, and water. Naturally, how are seamless steel pipes prevented from corroding? What are the technical requirements?
First, the technical requirements for corrosion prevention of seamless steel pipes.
Pipeline corrosion prevention: Corrosion prevention of seamless steel pipes requires adherence to drawings, using epoxy coal tar pitch wrapped with fiberglass cloth, and then applying a topcoat. The external wall construction process is as follows: Pipeline rust removal – Primer application – First coat of topcoat – Second coat of topcoat – Third coat of topcoat
1. Pipeline rust removal: Before applying the primer, the surface of the seamless steel pipe must be cleaned of oil, slag, rust, and iron oxide scale. Sandblasting is used for rust removal, achieving a quality standard of Sa2.5.
2. Rust Removal from Pipe Surface: After rust removal from the seamless steel pipe surface, apply primer. The time interval between rust removal and primer application should not exceed 8 hours. The substrate must be dry before applying primer. The primer should be applied evenly and fully, without lumps or bubbles. Do not apply primer to the area within 150-250mm from both ends of the seamless steel pipe.
3. Primer: After the primer surface is dry, apply the topcoat and wrap with fiberglass cloth. The time interval between applying the primer and the first coat of topcoat should not exceed 24 hours.
4. Material Specifications: The epoxy coal tar coating is a two-component, room-temperature curing type. The fiberglass cloth should be dry, dewaxed, untwisted, edge-sealed, medium-alkali, with a warp and weft density of 1012 threads/cm to 1212 threads/cm. The fiberglass cloth should be wrapped immediately after the topcoat is applied. The edge width of the fiberglass cloth should be 30-40mm, and the overlap length of the joint should not be less than 100mm. The overlaps of each layer should be staggered.
5. Fiberglass cloth oil impregnation rate: The fiberglass cloth must have an oil penetration rate of over 95%, and there should be no gaps larger than 50mm x 50mm. Seamless steel pipe ends require a 150-250mm stepped overlap.
6. Pipe joints: Pipe joint construction must be carried out after welding and pressure testing are passed. The overlap between the old and new anti-corrosion layers should be no less than 50mm, and the joint overlap length should be no less than 100mm. Joints must be firmly and tightly bonded.
7. Seamless steel pipe outer wall: The outer wall coating requirements for seamless steel pipes are: one primer layer, two topcoats, one fiberglass cloth layer, and two topcoats. The total dry film thickness is 400μm (micrometers).
8. Seamless steel pipe quality inspection: After the external anti-corrosion construction of the seamless steel pipe is completed, quality inspection must be carried out according to the design requirements or the corresponding requirements in the “Water Supply and Drainage Pipeline Engineering and Acceptance Specifications.”
Second, Pipeline Corrosion Inspection
1. Seamless Steel Pipe Coating Inspection and Acceptance
A. During and after surface coating construction, the coated workpiece should be protected to prevent dust and other debris from entering.
B. Post-coating inspection should ensure that the seamless steel pipe coating has a uniform color, bright and glossy appearance, and is free from obvious defects such as wrinkles, bubbles, runs, and missed areas. The coating thickness should be measured using a contact-type film thickness gauge, typically measuring at three points and taking the average.
2. Seamless Steel Pipe Quality Inspection
A. Quality inspection is conducted using sampling inspection according to design specifications.
B. Visual inspection of each pipe is performed. The coating surface should be uniform, flat, free of bubbles, wrinkles, bumps, and uneven edge pressing defects.
C. The paint film thickness is measured using a magnetic thickness gauge. Measurements are taken every 1.5 meters along the circumference at both ends and the middle of a single section of seamless steel pipe. The paint film thickness should meet two 85% requirements: 85% of the measuring points should meet the design thickness; for measuring points that do not meet the thickness, the minimum thickness should not be less than 85% of the design thickness.
D. Pinholes are inspected using a pinhole detector. If pinholes are found, they are sanded down and recoated using sandpaper and a grinding wheel.
E. If the paint film thickness is insufficient or pinholes are present, the coating should be repaired and cured. After repair, the coating should be re-inspected. Any defects must be repaired again until the coating is acceptable.
F. Adhesion is checked by making 60° angled cuts on the coating using a hard tool. The cuts should penetrate the coating to the substrate. The cuts are then taped to the surface. After removing the tape, the cuts are carefully observed; the coating should not peel off. Alternatively, a sample plate painted under the same conditions can be used for inspection.
Conclusion: Seamless steel pipes are steel pipes without welds, manufactured using hot-rolling and other heat-processing methods. If necessary, hot-worked steel pipes can be further cold-worked to the required shape, size, and properties. Currently, seamless steel pipes (DN15-600) are the most widely used steel pipes in petrochemical production plants.
Compared to ordinary steel pipes, seamless steel pipes can withstand higher pressures. Therefore, seamless steel pipes are used in industrial production where pipelines need to withstand high pressure. Some call them the “micro-vessels of industry,” as they are indispensable in manufacturing airplanes, ships, trains, and transporting oil, gas, and water. Naturally, how are seamless steel pipes prevented from corroding? What are the technical requirements?
First, the technical requirements for corrosion prevention of seamless steel pipes.
Pipeline corrosion prevention: Corrosion prevention of seamless steel pipes requires adherence to drawings, using epoxy coal tar pitch wrapped with fiberglass cloth, and then applying a topcoat. The external wall construction process is as follows: Pipeline rust removal – Primer application – First coat of topcoat – Second coat of topcoat – Third coat of topcoat
1. Pipeline rust removal: Before applying the primer, the surface of the seamless steel pipe must be cleaned of oil, slag, rust, and iron oxide scale. Sandblasting is used for rust removal, achieving a quality standard of Sa2.5.
2. Rust Removal from Pipe Surface: After rust removal from the seamless steel pipe surface, apply primer. The time interval between rust removal and primer application should not exceed 8 hours. The substrate must be dry before applying primer. The primer should be applied evenly and fully, without lumps or bubbles. Do not apply primer to the area within 150-250mm from both ends of the seamless steel pipe.
3. Primer: After the primer surface is dry, apply the topcoat and wrap with fiberglass cloth. The time interval between applying the primer and the first coat of topcoat should not exceed 24 hours.
4. Material Specifications: The epoxy coal tar coating is a two-component, room-temperature curing type. The fiberglass cloth should be dry, dewaxed, untwisted, edge-sealed, medium-alkali, with a warp and weft density of 1012 threads/cm to 1212 threads/cm. The fiberglass cloth should be wrapped immediately after the topcoat is applied. The edge width of the fiberglass cloth should be 30-40mm, and the overlap length of the joint should not be less than 100mm. The overlaps of each layer should be staggered.
5. Fiberglass cloth oil impregnation rate: The fiberglass cloth must have an oil penetration rate of over 95%, and there should be no gaps larger than 50mm x 50mm. Seamless steel pipe ends require a 150-250mm stepped overlap.
6. Pipe joints: Pipe joint construction must be carried out after welding and pressure testing are passed. The overlap between the old and new anti-corrosion layers should be no less than 50mm, and the joint overlap length should be no less than 100mm. Joints must be firmly and tightly bonded.
7. Seamless steel pipe outer wall: The outer wall coating requirements for seamless steel pipes are: one primer layer, two topcoats, one fiberglass cloth layer, and two topcoats. The total dry film thickness is 400μm (micrometers).
8. Seamless steel pipe quality inspection: After the external anti-corrosion construction of the seamless steel pipe is completed, quality inspection must be carried out according to the design requirements or the corresponding requirements in the “Water Supply and Drainage Pipeline Engineering and Acceptance Specifications.”
Second, Pipeline Corrosion Inspection
1. Seamless Steel Pipe Coating Inspection and Acceptance
A. During and after surface coating construction, the coated workpiece should be protected to prevent dust and other debris from entering.
B. Post-coating inspection should ensure that the seamless steel pipe coating has a uniform color, bright and glossy appearance, and is free from obvious defects such as wrinkles, bubbles, runs, and missed areas. The coating thickness should be measured using a contact-type film thickness gauge, typically measuring at three points and taking the average.
2. Seamless Steel Pipe Quality Inspection
A. Quality inspection is conducted using sampling inspection according to design specifications.
B. Visual inspection of each pipe is performed. The coating surface should be uniform, flat, free of bubbles, wrinkles, bumps, and uneven edge pressing defects.
C. The paint film thickness is measured using a magnetic thickness gauge. Measurements are taken every 1.5 meters along the circumference at both ends and the middle of a single section of seamless steel pipe. The paint film thickness should meet two 85% requirements: 85% of the measuring points should meet the design thickness; for measuring points that do not meet the thickness, the minimum thickness should not be less than 85% of the design thickness.
D. Pinholes are inspected using a pinhole detector. If pinholes are found, they are sanded down and recoated using sandpaper and a grinding wheel.
E. If the paint film thickness is insufficient or pinholes are present, the coating should be repaired and cured. After repair, the coating should be re-inspected. Any defects must be repaired again until the coating is acceptable.
F. Adhesion is checked by making 60° angled cuts on the coating using a hard tool. The cuts should penetrate the coating to the substrate. The cuts are then taped to the surface. After removing the tape, the cuts are carefully observed; the coating should not peel off. Alternatively, a sample plate painted under the same conditions can be used for inspection.
Conclusion: Seamless steel pipes are steel pipes without welds, manufactured using hot-rolling and other heat-processing methods. If necessary, hot-worked steel pipes can be further cold-worked to the required shape, size, and properties. Currently, seamless steel pipes (DN15-600) are the most widely used steel pipes in petrochemical production plants.
Post time: Apr-23-2026