Online Wear-Resistant Overlay Welding on Roller Presses: Lessons from Failure Analysis

Literature Overview

Pan Yuanchan's 2010 article in New Century Cement Herald documents a real-world failure investigation and resolution at Baoshan Kungang Jiahua Cement Building Materials Co., Ltd. The roller press was commissioned in August 2007, and during trial production, ferrous foreign objects entered the press and damaged portions of the roll surface. Because the damage area was small, it was initially left unrepaired. By May 2008, the roll surface exhibited spalling, reducing the crushing efficiency and affecting throughput.

Problem Description and Initial Repair Attempt

The first repair attempt used E707 (J707) electrodes directly on the damaged roll surface. The overlay layer spalled again within a short period. The authors correctly identified the root cause as incompatibility between the base material and the E707 electrode. E707 is a high-carbon, high-alloy electrode designed for high-wear applications, but when deposited directly on a medium-carbon low-alloy steel substrate without a transition layer, the mismatch in thermal expansion coefficient and carbon diffusion behavior leads to cracking and delamination.

Optimized Welding Procedure

After the initial failure, the welding procedure was optimized as follows:

1. Step 1: Apply a transition layer using E506 (J506) electrodes. This low-hydrogen, medium-carbon electrode provides a ductile, crack-resistant first layer that metallurgically bridges the gap between the base steel and the high-alloy overlay.
2. Step 2: Deposit the wear-resistant overlay layer using E707 electrodes.

This two-layer approach extended service life significantly compared to the single-layer E707 approach. However, the authors report that after 1 to 2 months of operation, spalling recurred, and in some cases, the base material itself began to spall.

Root Cause Analysis

The recurrence of spalling despite the two-layer approach warrants deeper metallurgical analysis. Several factors may contribute:

• Thermal cycling fatigue: Each welding pass subjects the surrounding base material to repeated heating and cooling cycles. If the base material has already been damaged by the original ferrous impact, its fatigue resistance is compromised.
• Residual stress accumulation: Multiple repair campaigns without proper stress relief accumulate residual tensile stresses in the HAZ, promoting crack initiation and propagation.
• Insufficient surface preparation: If the damaged area was not properly ground back to sound metal before welding, porosity and incomplete fusion defects remain as crack initiation sites.
• Welding sequence: The direction and sequence of bead placement affect the net residual stress state. Without a planned sequence, stress concentration can develop at bead toes.

Online Welding Considerations

The term "online" in this context means the welding is performed while the roller press remains in the production line, without complete disassembly of the roll. This introduces unique challenges:

• Limited access: Welding positions may be awkward, requiring careful electrode manipulation.
• Contamination risk: Cement dust and moisture in the ambient environment can introduce hydrogen into the weld, increasing cold cracking susceptibility.
• Thermal distortion: Localized heating of a large cylindrical shell can cause dimensional changes that affect roll-to-roll clearance.
• Inspection difficulty: Non-destructive testing (especially magnetic particle testing) is more challenging on a curved, in-situ surface.

Study Insights and Recommendations

This case study is a textbook example of how a seemingly minor repair can escalate into a chronic problem when the metallurgical fundamentals are not respected. The progression from initial damage, through an inadequate first repair, to recurring failure illustrates the importance of a systematic approach. I recommend that engineers adopt a formal FMEA (Failure Mode and Effects Analysis) for all overlay welding repairs on critical rotating equipment. The failure modes should be ranked by severity, occurrence, and detectability, and countermeasures should be implemented before the welding campaign begins. The two-layer approach with E506 transition and E707 overlay is sound in principle, but its success depends on strict adherence to preheating, interpass temperature control, and post-weld stress relief. Without these controls, even a metallurgically sound design will fail in service.