1. Cylinder Body Structure and Original Defects
| Compressor Component | Details |
|---|---|
| Rotor Diameter | φ816 mm |
| Compression Medium | LPG (Liquefied Petroleum Gas) |
| Cylinder Body Structure | Composed of inlet casing (cylinder head) and main cylinder body, with horizontal split structure for each section and vertical flange connection |
| Bearing Box Cover Material | Q235R |
- After the arrival of the ZG15Cr13 cylinder body casting blank, visual inspection revealed many repair marks on the outer surface. The casting allowance was calculated to be sufficient, and after photographing and recording the dimensions, the factory was allowed to proceed with the rough machining process.
2. Defects after Cylinder Body Machining
| Defect Location | Defect Type | Defect Size | Detection Standard |
|---|---|---|---|
| Bearing seat position and cylinder body parting surface edge | Long strip-shaped crack | Up to 150 mm | GB/T 9443 – 2019 I level (using solvent removal type, contrast test block B3) |
| Inner surface of the cylinder body near the center | Dense point defects | Up to 270 mm in a continuous strip shape | GB/T 9443 – 2019 I level (using solvent removal type, contrast test block B3) |
| Other positions on the inner cavity surface | Scattered point defects | – | GB/T 9443 – 2019 I level (using solvent removal type, contrast test block B3) |
- After the first cylinder body was detected with defects, it was judged as a nonconforming product and scrapped. The new cylinder body blank still had repair marks, and after machining, defects such as strip-shaped point defects and cracks were found. The owner agreed to the factory’s repair with concessions.
3. Casting Defect Repair Plan
| Repair Plan Aspect | Details |
|---|---|
| Defect Removal Method | Use a metal grinding head to remove point defects; drill φ5 mm crack arrest holes perpendicular to the inner surface for cracks (determine the drilling depth according to the crack depth and cylinder wall thickness) |
| Welding Method and Welding Material Selection | For deep defects, use E410 – 15 for manual welding as the base layer repair, and then use ER309L for argon arc welding with a remaining thickness of 1 – 2 mm on the surface; for near-surface small defects, only use ER309L for repair |
| Defect Nondestructive Testing Plan | Use surface penetration testing on the machined surface of the cylinder body, with a detection level of I in GB/T 9443 – 2019, using solvent removal type penetrant, extending the penetration and development time to 15 minutes, and cleaning the surface before testing |
| Repair Dimension Recheck | Check the flatness of the cylinder body parting surface with a dial indicator on the machine tool (allowing a slight depression within 0.10 mm), and check the runout value of the inner cavity surface with a tooling mandrel or on the machine tool (allowing a slight protrusion within 0.05 mm) |
| Repair Record and Traceability Management | Archive relevant documents such as defect records, repair processes, welding records, and test reports |
4. Implementation of Cylinder Body Defect Repair
- The welding repair was carried out according to the confirmed plan. The welding engineer of the casting supplier participated in the witness and guidance. The hardness of the weld bead on the test plate was controlled below 170 HB. The surface finish of the repaired area met the requirements, and the geometric tolerances met the deviation requirements. The cylinder passed the final penetration test.
5. Repair Result Verification
| Test Type | Test Conditions | Test Results |
|---|---|---|
| Pressure Resistance Test | Water pressure test at 0.81 MPaG for 1 hour (increased from the general 30 minutes), followed by a helium gas tightness test at 0.6 MPaG for 30 minutes (increased from the general 10 minutes) | The cylinder passed the tests successfully |
| Mechanical Operation and Performance Test | Using air as the medium, continuous operation for 4 hours with the highest exhaust temperature reaching 160 °C and the exhaust pressure maintained at about 0.060 MPaG | The unit operated smoothly and passed the test |
6. Quality Comparison of the Improved Cylinder Body Casting
- The new casting blank of the improved cylinder body has better surface finish, fewer local repair marks, and no excessive crack defects on the inner cavity surface after machining. Only some small cracks and sand holes in non-core areas were found, and the owner agreed to use a special curing agent for filling.
7. Conclusion
- The welding repair of the ZG15Cr13 martensitic material casting cylinder body can ensure the long-term stable operation of the unit, but a detailed and rigorous repair plan is required. Reducing or even eliminating casting defects from the source is of great significance. It requires the comprehensive cooperation of technology improvement, personnel management, and cost control.