CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Weld Overlay Repair Technology for Diesel Engine Bodies
Literature Overview
Published in the journal Hot Working Technology in 2024, this paper by Yang Feiyu from the Naval Equipment Department and Zhang Jie, Sun Yubo, and Lu Long from Shaanxi Diesel Engine Heavy Industry Co., Ltd. presents a comprehensive study on weld overlay repair technology for diesel engine bodies. This is a highly relevant and timely paper given the increasing emphasis on equipment maintenance, repair, and overhaul (MRO) in the maritime and naval sectors, where diesel engine reliability is critical to operational readiness.
Technical Background
Diesel engine bodies, particularly the main bearing saddles, crankcase webs, and cylinder block surfaces, are subjected to severe mechanical loading, thermal cycling, and vibrational fatigue during operation. Wear, scoring, and dimensional deviation of these critical surfaces can occur over extended service periods, necessitating repair through weld overlay techniques to restore original dimensions and surface integrity.
The repair of diesel engine bodies presents unique challenges compared to new manufacturing because the repair must be performed on an already-stressed component with complex geometry, often without complete disassembly. The repair overlay must restore both dimensional accuracy and mechanical properties, including fatigue strength and stress corrosion resistance, to ensure that the repaired component performs equivalently to the original.
| Repair Location | Typical Defect | Overlay Material | Process |
|---|---|---|---|
| Main bearing saddle | Wear scoring, dimensional deviation | Low-carbon steel, 12CrMoV | SAW or GTAW overlay |
| Crankcase web | Cracking, fatigue damage | Low-alloy steel | Multi-pass GTAW with stress relief |
| Cylinder block bore | Out-of-round, scoring | Wear-resistant alloy | SAW overlay followed by machining |
| Thrust bearing surface | Excessive wear | Bronze or nickel-aluminum bronze | PTA or laser cladding |
Process Development and Key Parameters
The paper documents the development of a systematic repair methodology that includes surface preparation, preheating, multi-pass overlay welding, post-weld machining, and final inspection. Surface preparation involves grinding away the damaged surface to a sound metal substrate, followed by cleaning to remove oil, coolant, and other contaminants that could cause porosity or lack of fusion.
Preheating is essential for diesel engine body repairs because the thick sections of the engine body create high thermal mass, and insufficient preheating can lead to excessive cooling rates that promote martensite formation and cracking in the weld metal. Preheat temperatures of 200-350 degrees Celsius are typically applied, depending on the base material composition and section thickness.
The overlay welding process is executed in multiple passes, with the first pass designed to create a sound metallurgical bond to the base material and subsequent passes building up the required material volume for machining back to nominal dimensions. The interpass temperature must be maintained within a controlled range of 250-400 degrees Celsius to prevent excessive hardness in the heat-affected zone while ensuring adequate wetting of each successive pass.
Quality Assurance and Inspection
Quality control for diesel engine body repairs is stringent because these components are safety-critical. The inspection protocol typically includes visual examination of the repair area, magnetic particle testing to detect surface cracks, ultrasonic testing to verify absence of internal defects, and dimensional inspection to confirm that the machined surface meets original specifications.
The metallurgical quality of the repair is verified through hardness testing across the weld cross-section to ensure a gradual transition from base material to overlay material without abrupt hardness peaks that could serve as crack initiation sites. Microstructural examination may also be performed to confirm the absence of harmful phases and to verify proper heat treatment response.
Engineering Practice and Lessons Learned
The paper emphasizes the importance of a systematic approach to repair welding, including careful documentation of the repair procedure, control of all welding parameters, and thorough inspection at each stage. The authors also highlight the value of post-weld stress relief annealing, which is particularly important for thick-section engine bodies where residual stresses can be significant and may promote fatigue cracking during subsequent service.
This study provides valuable practical guidance for maintenance engineers and welders working on diesel engine repairs, offering a structured methodology that can be adapted to different engine models and damage scenarios. The systematic approach to repair welding documented in this paper reflects best practices in the field and contributes to the growing body of knowledge on in-service repair of critical mechanical components.