For PTFE lined steel piping systems, quality control should cover both the internal fluoropolymer lining and the external steel structure.
The PTFE lining protects the pipe from corrosive process media, while the steel shell provides mechanical strength and pressure resistance. The external coating system helps protect the steel surface during storage, transportation, installation and long-term industrial service.
As part of our production quality control process, Jiangsu Yihao recently carried out a series of external coating inspections on a batch of PTFE lined steel pipes.
The inspection included:
- Dry film thickness measurement
- Pull-off adhesion testing
- Steel surface profile inspection
- Visual examination of finished pipe surfaces
- Inspection of pipe bodies, flanges and transition areas
Coating Test Panels Prepared with the Production Batch
Coating test panels were prepared under conditions consistent with the actual production batch.
The panels were coated using the same or corresponding surface preparation and coating procedures applied to the finished PTFE lined steel pipes. Multiple inspection points were marked on each panel for coating thickness and adhesion testing.
These test panels help our quality team evaluate the consistency of the coating process before the products are released for packing and delivery.
They are not only color samples. They provide measurable evidence of coating performance and process stability.
Dry Film Thickness Measurement
A professional electronic coating thickness gauge was used to measure the dry film thickness of the coated surfaces.
Measurements were taken at multiple positions on the test panels and finished pipes, including:
- Straight pipe sections
- Areas close to the flanges
- Welded and fabricated sections
- Different spraying positions around the pipe circumference
The coating thickness readings shown during this inspection were generally within approximately 400–469 μm at the measured locations.
Multi-point inspection is important because coating thickness may vary depending on pipe geometry, spraying angle and local surface conditions.
The final acceptance criteria are determined according to the approved coating specification, project requirements and coating system recommendations.
A thicker coating is not automatically a better coating. Proper performance depends on achieving a controlled and uniform dry film thickness without excessive build-up, insufficient coverage, sagging or other coating defects.
Pull-Off Adhesion Testing
Pull-off adhesion testing was performed to evaluate the bonding strength between the coating system and the steel substrate.
During the test, loading fixtures were bonded to the coated test panels. After the adhesive had cured, a hydraulic adhesion tester was used to apply perpendicular tensile force until separation occurred.
Several recorded test values were within approximately 16.25–22.10 MPa at the corresponding inspection points.
In addition to the numerical result, the failure mode was also examined. This helps determine whether separation occurred:
- Between the coating and steel substrate
- Between individual coating layers
- Within the coating itself
- Within the adhesive used for the test fixture
The failure mode is an important part of the evaluation because a single numerical value does not fully describe coating performance.
Any abnormal or inconsistent result must be reviewed together with the fixture bonding condition, test position and failure surface before a final judgment is made.
Steel Surface Profile Inspection
The condition of the steel surface before coating has a major influence on coating adhesion and long-term durability.
A surface profile gauge and replica tape system were used to inspect the prepared steel surface.
A suitable surface profile increases the effective contact area between the primer and the steel substrate. It also provides mechanical anchoring for the coating system.
If the surface preparation is insufficient, the coating may not achieve proper adhesion. If the surface profile is too aggressive, the coating may fail to fully cover the profile peaks.
For this reason, our coating process controls several factors together:
- Surface cleanliness
- Surface roughness
- Dust and contamination removal
- Time interval between preparation and coating
- Ambient conditions during coating application
Inspection of Finished PTFE Lined Steel Pipes
After the test panels were evaluated, coating thickness measurements were also taken directly on the finished PTFE lined steel pipes.
Inspection was not limited to the center of the straight pipe body. Additional attention was given to areas where coating thickness can be more difficult to control, such as flange edges, welded sections and structural transition areas.
The finished surfaces were also visually inspected for possible defects, including:
- Missed coating areas
- Uneven coating thickness
- Sagging or excessive coating build-up
- Pinholes and bubbles
- Mechanical damage
- Surface contamination
Only after the required inspection steps are completed are the pipes prepared for protection and packing.
Internal Corrosion Resistance and External Protection
A PTFE lined steel pipe combines the advantages of two different materials.
The external steel shell provides structural strength, while the internal PTFE lining isolates the steel from corrosive chemicals.
The external coating provides an additional protective layer for the steel structure. It is especially important during:
- Outdoor storage
- Marine transportation
- On-site installation
- Operation in humid industrial environments
- Exposure to corrosive industrial atmospheres
For this reason, the quality of a PTFE lined piping system should not be evaluated only by its internal lining.
A complete inspection process should also cover steel fabrication, welding quality, dimensional accuracy, flange condition, external coating and packing protection.
Quality Is Verified at Every Production Stage
At Jiangsu Yihao, quality control is integrated into the manufacturing process.
From surface preparation and coating application to thickness measurement, adhesion testing, visual inspection and final packing, each stage is checked according to the relevant project and production requirements.
Our goal is to provide reliable PTFE lined pipes, fittings and corrosion-resistant equipment for demanding chemical processing applications.
Quality is checked, not assumed.
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