Overlay Welding Repair and Maintenance of Imported Roller Press Roller Surfaces

Literature Overview

The paper by Fu Jinqiang from Gezhouba Group Cement Co., Ltd., published in New Century Cement Bulletin (2012, Vol. 18, Issue 5, pp. 58-59), documents a significant failure case and successful repair of a German-made Humboldt Φ1400×500 roller press used in cement grinding. The roller surface experienced extensive spalling due to accumulated welding stress from multiple field repair welds, and a through-thickness crack reaching 180 mm depth was discovered. The replacement of the roller sleeve and subsequent overlay welding repair achieved service life exceeding that of a new roller. This case study provides valuable lessons for engineers managing heavy grinding equipment in cement and mineral processing industries.

Failure Mechanism Analysis

Root Cause Investigation

The failure of the roller press surface was traced to a cascade of contributing factors:

• Fatigue damage: The roller surface accumulated fatigue damage from repeated compressive loading during cement grinding operations.
• Repeated field welding: Multiple in-situ repair welds introduced cumulative residual stresses without adequate stress relief between repairs.
• Welding stress accumulation: Each repair weld added new residual stresses to the existing stress field, progressively degrading the material's fatigue resistance.
• Spalling initiation: Surface fatigue cracks propagated and coalesced, leading to material spalling from the roller surface.
• Through-thickness crack: The accumulated damage eventually produced an axial crack penetrating 180 mm into the roller sleeve, threatening complete fracture.

Defect Characterization

Repair Strategy and Implementation

Sleeve Replacement Approach

When the 180 mm deep axial crack was discovered after machining away the spalled overlay layer, the decision was made to replace the roller sleeve entirely rather than attempt to repair the cracked base. This conservative approach was justified because:

1. The crack depth represented a significant proportion of the sleeve wall thickness.
2. Repair welding of a pre-existing crack in a heavily stressed component carries high risk of incomplete crack closure.
3. The cost of sleeve replacement was justified by the criticality of the roller press to production continuity.

Overlay Welding Repair of New Sleeve

After installing the new sleeve, a wear-resistant overlay layer was applied using appropriate welding materials and procedures:

• Welding material selection: Hardfacing alloy with appropriate hardness (typically 45-55 HRC) and impact resistance for cement grinding service.
• Welding process: Multi-pass overlay welding with controlled heat input to minimize dilution and residual stress.
• Preheating: Moderate preheat (100-150 °C) to control cooling rate without excessive softening of the base metal.
• Post-weld treatment: Stress relief annealing to reduce residual stresses in the overlay and base metal.

Maintenance Experience and Best Practices

The paper distills several critical maintenance principles from this failure case:

1. Iron removal: Thorough removal of tramp iron from feed material prevents premature abrasive wear and surface damage.
2. Material ratio control: Proper control of the material composition and feed rate prevents excessive localized loading on the roller surface.
3. Regular inspection: Systematic periodic inspection of the roller surface (using UT, MT, or eddy current methods) enables early detection of subsurface cracks before they reach critical depth.
4. Welding material selection: Choosing overlay materials that match the service conditions (abrasion resistance, impact resistance, fatigue resistance) is essential for long-term performance.
5. Repair methodology: Field repair welding must include proper preheat, interpass temperature control, and post-weld stress relief—each repair is an opportunity to either improve or degrade the component's condition.
6. Manufacturer selection: Qualified welding contractors with experience in roller press repair should be engaged for overlay welding work.

Engineering Practice Integration

This case study has direct relevance to pipe and fitting manufacturing, particularly in the context of:

• Roll forming equipment: Rollers used in pipe roll forming and fitting bending machines experience similar fatigue and surface damage mechanisms.
• Calibration rollers: Rollers used in pipe calibration and sizing operations require periodic overlay repair.
• Field repair philosophy: The lesson about cumulative welding stress from repeated repairs applies equally to field repair of pipe welds and fitting joints.

The FMEA (Failure Mode and Effects Analysis) perspective applied to this case reveals that the root cause was not a single event but a systemic failure of the maintenance strategy. The repeated field welding without stress relief represents a "repair-induced degradation" mode that is common in industrial equipment maintenance. Each repair, if not properly executed, reduces the remaining fatigue life of the component.

Key Reflections

The most important lesson from this paper is that maintenance welding is not maintenance—it is a modification that introduces new stresses, new microstructures, and new potential failure sites. The roller press sleeve that was repaired multiple times in the field eventually failed catastrophically because each repair weld added to the cumulative stress state without providing stress relief.

For engineers in the piping industry, this translates to a critical principle: when repairing a weld or overlay on a pressure-containing component, the repair must be designed to restore or exceed the original component's fatigue resistance. This requires not just proper welding technique but also comprehensive stress management—preheating, interpass temperature control, post-weld heat treatment, and verification testing.

The success of the sleeve replacement and re-overlay in achieving better-than-new performance demonstrates that proper engineering intervention, when done correctly, can outperform the original design. The new sleeve, properly overlaid with the correct materials and procedures, exceeded the service life of the original roller. This outcome validates the investment in thorough failure analysis and proper repair methodology over the short-term cost savings of repeated quick fixes.