Zhuojin Pipe Fitting Co., LtdCompilation Qualification and Application of Hard Alloy Overlay Welding Procedure Specifications
Literature Overview
This paper by Liu Yuan, Shi Xuefen, Li Yan, and Guo Jing, published in Chemical Equipment Technology (Volume 32, Issue 1, 2011, pages 28-34), presents a practical case study on the compilation, qualification, and application of hard alloy overlay welding procedure specifications in accordance with ASME Code Section IX requirements. The authors, affiliated with Dalian Hitachi Machinery Equipment Co., Ltd., address several critical aspects of overlay welding procedure development for pressure vessel components. This work is of significant practical value to welding engineers involved in the fabrication of pressure vessels, heat exchangers, and other critical equipment where hard-facing overlay is required for erosion and wear resistance.
ASME Code Section IX Framework for Overlay Welding
The paper emphasizes the rigorous framework provided by ASME Code Section IX for the qualification of overlay welding procedures. Under ASME IX, overlay welding falls under Part Q, which governs welding procedure and performance qualification for overlay welding. The qualification process requires the development of a Welding Procedure Specification (WPS) that defines all essential variables, followed by the execution of a Welding Procedure Qualification Record (WPQR) that documents the actual welding parameters and the results of required tests.
The essential variables for overlay welding under ASME IX include factors such as welding process, filler metal classification, preheat and interpass temperature, heat input, backing gas, and the number of layers. For hard alloy overlay welding, additional considerations include the type of hard alloy (e.g., cobalt-based, iron-based, or nickel-based), the carbon content, the presence of carbide-forming elements such as chromium, tungsten, molybdenum, and vanadium, and the dilution control between the overlay layer and the base metal.
| ASME IX Requirement | Description | Engineering Significance |
|---|---|---|
| WPS development | Defines all welding parameters | Ensures reproducibility and consistency |
| WPQR execution | Documents actual welding and test results | Provides qualification evidence |
| Essential variables | Critical parameters that must be controlled | Prevents unqualified process deviations |
| Dilution testing | Measures base metal dilution in overlay | Ensures hardness and wear resistance |
| Hardness testing | Verifies overlay hardness meets specifications | Confirms functional performance |
| Visual inspection | Checks for surface defects | Ensures quality and safety |
Procedure Qualification Process
The paper describes a step-by-step approach to procedure qualification for hard alloy overlay welding. The process begins with the selection of the appropriate welding process based on the application requirements. For hard alloy overlay, processes such as submerged arc welding (SAW), plasma arc welding (PAW), gas tungsten arc welding (GTAW), and shielded metal arc welding (SMAW) are commonly used. Each process has distinct advantages: SAW offers high deposition rates and deep penetration, PAW provides precise control and low dilution, GTAW offers excellent arc stability and low dilution, and SMAW provides flexibility for field applications.
The selection of filler metal is a critical step in the qualification process. Hard alloy filler metals are typically classified according to AWS or ISO standards, with specific designations indicating the composition and intended application. For example, AWS A5.15 classifies hard-facing electrodes and rods for SAW, SMAW, and GTAW processes. The selection must account for the base metal composition, the service environment (temperature, corrosive media, impact loading), and the required hardness level.
The dilution control is particularly important for hard alloy overlay welding. Dilution refers to the mixing of base metal into the overlay layer during welding, which can significantly reduce the hardness and alter the microstructure of the overlay. For hard alloy overlays, dilution must be carefully controlled to ensure that the overlay retains its designed hardness and wear resistance properties. The paper discusses methods for controlling dilution, including the use of multiple overlay layers, the selection of appropriate welding parameters (such as lower heat input), and the use of transition layers between the base metal and the hard alloy overlay.
Application Case Study
The paper presents a specific case study involving the hard alloy overlay welding of a pressure vessel component. The case demonstrates the practical application of the ASME IX qualification process, from WPS development through WPQR execution to the final application in production. The authors highlight several challenges encountered during the qualification process, including the control of dilution, the prevention of cracking in the overlay layer, and the achievement of consistent hardness across the overlay surface.
One of the key challenges in hard alloy overlay welding is the prevention of cracking. Hard alloy overlays often contain high carbon and carbide-forming elements, which can lead to the formation of brittle microstructures susceptible to cracking during cooling. The paper discusses countermeasures such as the use of preheating, the control of interpass temperature, the selection of appropriate filler metals with lower carbon content for the transition layer, and the use of post-weld heat treatment to relieve residual stresses.
Another important aspect discussed in the paper is the inspection and acceptance criteria for hard alloy overlay welds. The paper emphasizes the importance of visual inspection, hardness testing, and, in some cases, non-destructive testing such as magnetic particle inspection (MT) or ultrasonic testing (UT) to ensure the quality of the overlay welds. The acceptance criteria must be defined in the WPS and must be consistent with the applicable code requirements and the service conditions of the component.
Engineering Practice and Quality Control
From a quality control perspective, the paper underscores the importance of maintaining a systematic approach to overlay welding procedure qualification and application. The use of documented WPS and WPQR ensures that the welding process is controlled and traceable, which is essential for meeting code requirements and ensuring the safety and reliability of pressure vessel components.
The paper also highlights the importance of welder qualification for overlay welding. Welders performing hard alloy overlay welding must be qualified according to ASME IX requirements, which include the demonstration of their ability to produce welds that meet the specified requirements for the applicable welding process and filler metal. The qualification of welders for overlay welding may involve additional requirements beyond those for base metal welding, such as the demonstration of their ability to control dilution and achieve consistent hardness in the overlay layer.
Study Insights and Reflections
This paper provides a valuable practical guide for welding engineers involved in hard alloy overlay welding. The emphasis on ASME IX compliance and the systematic approach to procedure qualification is commendable and reflects the importance of code compliance in the fabrication of pressure vessel components. The case study approach used in the paper is particularly effective in illustrating the practical challenges and solutions encountered in overlay welding.
One reflection from this study is the importance of integrating metallurgical understanding with procedural requirements. While ASME IX provides a framework for procedure qualification, the actual success of the overlay welding process depends on a deep understanding of the metallurgical interactions between the base metal and the overlay material. Engineers must be able to select appropriate filler metals, control welding parameters, and implement quality control measures based on metallurgical principles rather than simply following code requirements.
Another reflection is the need for continuous improvement in overlay welding practices. As new materials and applications emerge, the existing code requirements may need to be updated or supplemented with additional testing and qualification criteria. Engineers should stay informed about the latest developments in overlay welding technology and materials to ensure that their practices remain current and effective.
Summary
This paper presents a comprehensive approach to the compilation, qualification, and application of hard alloy overlay welding procedure specifications in accordance with ASME Code Section IX. The authors demonstrate the importance of a systematic approach to procedure qualification, including the development of WPS, the execution of WPQR, the control of essential variables, and the implementation of quality control measures. The case study provides practical insights into the challenges and solutions encountered in hard alloy overlay welding of pressure vessel components. This work is essential reading for welding engineers involved in the fabrication of critical equipment where hard-facing overlay is required for erosion and wear resistance.