Preparation Qualification and Application of Hardfacing Process Specification for Pressure Vessel Components

Literature Overview

The paper by Liu Yuan, Shi Xuefen, Li Yan, and Guo Jing, published in Chemical Equipment Technology in 2011 (Vol. 32, No. 1, pp. 28-34), presents a practical case study on the preparation, qualification, and application of a hardfacing welding process specification in accordance with ASME Section IX requirements. Authored by engineers from Dalian Hitachi Machinery Equipment Co., Ltd., this work addresses a frequently encountered challenge in the pressure vessel industry: the systematic development and documentation of hardfacing procedures that satisfy code requirements while ensuring adequate performance of the deposited overlay.

Core Technical Content

The paper walks through a specific pressure vessel component hardfacing example, covering the following key aspects:

Process Specification Preparation: The authors detail the step-by-step development of a Welding Procedure Specification (WPS) for hardfacing, including the selection of welding process, electrode classification, preheat temperature, interpass temperature, and post-weld treatment.
Welding Procedure Qualification: The qualification process follows ASME Section IX Part Q, including the determination of essential and non-essential variables specific to overlay welding.
Application Considerations: Practical issues encountered during production implementation are discussed, including consumable selection, surface preparation, and quality verification methods.

ASME Section IX Variable	Hardfacing Specific Requirement
Welding Process	Process group number and P-number of base material
Filler Metal	F-number classification and electrode type
Preheat Temperature	Minimum preheat based on base material carbon equivalent
Interpass Temperature	Maximum interpass temperature to control dilution
Post-Weld Treatment	Stress relief requirements if applicable
Essential Variables	Includes electrode diameter, travel speed, and heat input

Engineering Practice Analysis

Hardfacing qualification under ASME Section IX is notably different from butt-welding qualification in several important respects. The most significant difference is that the primary objective of hardfacing is surface performance (hardness, wear resistance, corrosion resistance) rather than joint strength. However, the ASME code still requires demonstration of adequate mechanical properties including tensile strength and hardness of the deposited metal.

In practice, engineers frequently encounter the following challenges:

Dilution Control: The dilution of base metal into the overlay directly affects the hardness and composition of the deposited layer. The qualification procedure must account for dilution effects, and the qualified procedure should specify acceptable dilution limits.
Cracking Susceptibility: Hardfacing alloys, particularly those with high carbon and alloy content, are prone to cracking during deposition. The WPS must include appropriate preheat and interpass temperature requirements to prevent hot cracking and cold cracking.
Surface Preparation: The quality of the transition zone between the base material and the overlay is critical. Surface roughness, contamination, and geometry all affect the bonding quality and mechanical properties of the hardfacing deposit.

Key Questions and Reflections

One of the most valuable aspects of this paper is its focus on the practical implementation of code requirements rather than purely theoretical considerations. In my experience, many engineers struggle with the transition from laboratory-qualified procedures to production application, where variables such as operator skill, equipment consistency, and environmental conditions can significantly affect results. The paper correctly emphasizes that the WPS is not merely a document but a living process specification that must be continuously monitored and updated based on production experience.

The ASME Section IX qualification approach for hardfacing, while rigorous, can sometimes be overly conservative for non-pressure-containing applications. Engineers working on non-code equipment should consider whether simplified qualification approaches are appropriate, provided they can demonstrate adequate performance through alternative verification methods. This paper serves as an excellent reference for engineers new to the hardfacing qualification process and provides a practical framework for developing code-compliant overlay welding procedures.