Wear-Resistant Cladding Layer Testing and Technical Application for Coal Chemical Equipment

Literature Overview

This 2015 publication by Chen Sunyi from Maoming Gravity Petrochemical Machinery Manufacturing Co., Ltd. addresses the critical challenge of abrasive wear in coal chemical equipment. Coal chemical processing environments are uniquely harsh, involving high-temperature gas-solid two-phase flow, chemical corrosion, and mechanical abrasion simultaneously. The study focuses on developing and validating wear-resistant overlay layers specifically tailored for coal chemical equipment operating conditions. The research context reflects the rapid expansion of China's coal chemical industry during the 2010s, where equipment longevity directly impacts operational economics and safety.

Core Technical Points

The study investigates overlay welding as a primary surface engineering solution for extending the service life of coal chemical equipment components. Key technical considerations include the selection of overlay materials with adequate hardness and wear resistance, the welding process parameters that ensure proper metallurgical bonding, and the durability of the overlay layer under actual service conditions.

The authors emphasize that coal chemical equipment faces a complex degradation mechanism that differs significantly from conventional petrochemical equipment. The abrasive particles in coal-derived syngas, combined with corrosive species such as H₂S and CO₂, create a synergistic attack that accelerates material failure beyond what either mechanism would cause independently.

Material Selection and Microstructural Considerations

Parameter	Specification
Base material	Carbon steel / Low-alloy steel
Overlay material candidates	High-carbon martensitic steel, carbide-containing alloy
Target hardness	50-60 HRC minimum
Overlay thickness	3-5 mm typical
Welding process	Multi-pass submerged arc or shielded metal arc
Preheat temperature	200-300 °C
Interpass temperature	Controlled below 250 °C

The microstructural evolution in the overlay layer is critical to achieving the desired wear resistance. High-carbon martensitic structures provide hardness through solid solution strengthening and precipitation of hard carbide phases. The transition zone between the base metal and overlay layer must be carefully managed to prevent cracking during thermal cycling in service.

Process Analysis and Engineering Application

The study demonstrates that multi-pass overlay welding with controlled thermal input is essential for achieving uniform hardness distribution throughout the overlay layer. Single-pass application often results in excessive dilution from the base metal, reducing the effective hardness below acceptable levels. The recommended approach involves depositing a transition layer to manage carbon diffusion and residual stress before applying the final wear-resistant layer.

Defect Analysis and Countermeasures

Defect Type	Root Cause	Countermeasure
Cracking in transition zone	Excessive thermal stress, high carbon concentration	Preheat, controlled cooling rate, low-carbon transition layer
Poor bond strength	Incomplete fusion, oxide inclusion	Surface preparation, flux selection, adequate heat input
Hardness variation	Dilution from base metal, uneven cooling	Multi-pass strategy, proper travel speed
Spallation during service	Thermal mismatch, cyclic loading	Stress relief annealing, controlled overlay geometry

Engineering practice in coal chemical plants has shown that proper overlay application can extend equipment life by 3-5 times compared to uncoated components. The economic analysis must account for the initial cost of overlay welding versus the replacement frequency of unprotected components. In high-severity service environments, the investment in quality overlay welding is readily justified by reduced maintenance downtime and extended equipment availability.

Study Insights and Implications

The research underscores that wear-resistant overlay for coal chemical equipment is not merely a hardness problem but a holistic engineering challenge requiring consideration of thermal cycling resistance, corrosion-abrasion synergy, and residual stress management. The transition layer concept is particularly important in thick overlay applications where differential cooling rates between the overlay and base metal can generate significant residual stresses that compromise long-term reliability. Engineers should prioritize process validation through coupon testing that simulates actual service conditions, including thermal cycling and chemical exposure, rather than relying solely on static hardness measurements.