Case Studies in Wear Resistance Using HVOF, PTAW and Spray Fusion Surfacing

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Courtesy of Castolin Eutectic

Abstract
Extensive laboratory testing and field usage have shown that innovative surfacing techniques have produced cost effective maintenance systems and are providing long-term benefits. Self-fusing (sometimes known as self-fluxing) alloys containing tungsten carbide (WC), applied by PTAW, HVOF and SF (Spray Fusion) brazing processes are investigated. The process used and the effect of process parameters on the wear resistance of these coatings is evaluated. The test results show that the same self-fusing alloy applied by SF compared to PTAW have proven superior in severe erosive and abrasive applications. The case histories presented will cover a variety of applications including the use of HVOF versus hard chrome plating and the improvement in wear resistance of SF applied self-fused coatings versus PTAW. These comparisons are useful in providing new, higher performance solutions, in helping to overcome today's tougher surfacing and environmental requirements

Introduction
The commercial use of thermal spray coatings and advanced weld surfacing technologies is gaining increased support worldwide. Recently, alternatives to hard chrome plating have been sought due to the environmental hazards associated with this process [1-4]. The HVOF process is one of several alternatives (PVD, CVD, nitriding etc.) that have replaced hard chrome plating in industries such as aircraft, oil and gas, petrochemical, and pulp and paper, where hard frictional wear resistance is required.

A limitation with the HVOF process is that coating thickness is relatively thin (less than 2mm). For applications where thicker coatings (greater than 2mm) are required for resistance to erosion, and impact loading, traditional processes such as SAW, FCAW, and PTAW are used. Self-fusing powder alloys based on nickel-boron-silicon (Ni/B/Si), with the addition of chromium (Cr) and tungsten carbide (WC) have shown excellent resistance to abrasion and erosion.

Acceptance by primary resource-based industries in Western Canada is growing. Many dedicated repair shops have invested heavily in surfacing processes in order to offer industry improved wear preventive solutions. HVOF and PTAW processes are in regular use, providing a solid infrastructure for reliable surfacing application. By having local dedicated services, the market continues to expand and new uses are sought and realized for surfacing technologies. Using reliable, high production spray systems, and automation packages, these repair shops have been able to gain quality and productivity advantages. The market will continue to drive the use of these innovative technologies, in part due to increasingly severe production demands, cost reduction strategies, environmental concerns and explicit profit expectations.

This paper presents some new applications in the oil and gas, and pulp and paper industries, where significant cost efficiencies have been experienced. The case histories presented will cover a variety of applications including:

  • The use of HVOF to produce improved wear resistant overlays compared to hard chrome plating in the pulp & paper industry.
  • The use of SF brazing to produce improved wear resistant spray fused overlays compared to the same material applied by PTAW in the oil and gas Industry.

The challenge is to meet these demands with specific, cost effective surfacing technologies and to liaison closely with industrial experts to support these services effectively.

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