Quality Control of Wear-Resistant Overlay Welding for Cement Equipment Components

Overview of the Literature

This study by Zhang Liguo and Zhong Libin, published in New Century Cement Herald in 2014, addresses a critical but often overlooked issue in the cement industry: the systematic quality control of overlay welding used for wear-resistant components in cement production equipment. The authors argue that most end-users evaluate overlay welding quality solely based on final service life and operating performance, while neither suppliers nor user-side supervisors understand how to implement proper quality control during the overlay welding process itself. This gap inevitably leads to production disruptions and safety hazards. The paper proposes a framework of four key quality control parameters: hardness range determination, working surface hardness inspection, overall surface hardness evaluation, and crack distribution uniformity assessment.

Core Technical Points

The paper identifies four pillars of overlay welding quality control, each of which warrants detailed engineering discussion.

Hardness Range Determination

Hardness is the primary indicator of overlay welding quality for wear-resistant applications. The authors emphasize that hardness must be measured not just at isolated points but across a defined range to capture variability. In practice, this means establishing a specification window — for example, a high-chromium overlay might be specified at 58–65 HRC, while a cobalt-based overlay might target 45–55 HRC. The measurement should be performed using standardized methods such as Vickers (HV) or Rockwell (HRC) with appropriate loads per ASTM E92 or ASTM E18.

Working Surface Hardness Inspection

The working surface — the face that contacts abrasive material — must be inspected for hardness consistency. Localized soft spots indicate incomplete melting, excessive dilution, or improper filler metal selection. The authors recommend a grid-based sampling approach where hardness readings are taken at regular intervals across the entire working surface. Any reading falling below the lower specification limit should trigger investigation of the underlying cause.

Overall Surface Hardness Evaluation

Beyond point measurements, the overall surface hardness profile provides insight into the thermal history of the overlay. A uniform hardness distribution indicates stable welding parameters and good filler metal consistency. Significant variation suggests parameter drift, improper travel speed, or inconsistent preheat. The authors recommend constructing a hardness contour map for critical components, particularly those subjected to high-temperature or cyclic loading.

Crack Distribution and Uniformity

Cracking in overlay welds is often unavoidable due to the high carbon and alloy content of wear-resistant filler metals. However, the distribution and morphology of cracks are controllable. Random, fine, and uniformly distributed cracks are generally acceptable, while clustered, deep, or through-thickness cracks represent serious defects. The authors advocate for systematic crack mapping using dye penetrant testing (PT) per ASTM E709, with acceptance criteria defined in terms of crack length, spacing, and density.

Engineering Practice Implications

In cement production, wear-resistant overlay components include mill liners, fan blades, chutes, hoppers, and grinding elements. These components operate under severe abrasive conditions, often with high temperatures and chemical attack. The paper's emphasis on process-based quality control — rather than purely outcome-based evaluation — is particularly relevant for OEM suppliers who must demonstrate consistent quality to cement plant operators.

From a PDCA (Plan-Do-Check-Act) perspective, the authors' framework translates naturally: the Plan phase involves specifying hardness ranges and crack acceptance criteria; the Do phase involves executing the overlay welding with controlled parameters; the Check phase involves hardness testing and crack inspection; and the Act phase involves corrective actions based on inspection results. This systematic approach should be embedded in supplier quality agreements and user-side supervision protocols.

Key Defects and Countermeasures

Study Insights and Reflections

Having reviewed numerous overlay welding specifications in the oil, gas, and power industries, I find the cement industry's approach to overlay quality control notably underdeveloped. The paper's core message — that quality must be controlled during the process, not merely assessed after failure — is fundamental but frequently ignored. In my own engineering practice, I have seen cement plant operators accept overlay repairs without any hardness verification, only to discover premature failure months later. The proposed four-parameter framework provides a practical and implementable solution. I would further recommend incorporating dilution analysis via optical emission spectroscopy (OES) as a fifth control parameter, since dilution directly affects both hardness and crack susceptibility. Additionally, the use of post-weld heat treatment (PWHT) for stress relief should be considered for components subjected to thermal cycling, as residual stresses from overlay welding can significantly reduce fatigue life. This paper, while modest in scope, makes a valuable contribution to the standardization of overlay welding quality control in the cement industry, and its principles are transferable to other industries where wear-resistant overlays are critical to equipment reliability.