Compilation Evaluation and Application of Hardfacing Process Specifications

Literature Overview

This 2011 publication by Liu Yuan, Shi Xuefen, Li Yan, and Guo Jing from Dalian Hitachi Machinery Equipment Co., Ltd., published in Chemical Equipment Technology (化工装备技术), takes a distinctly practical approach to hardfacing process development. Unlike purely academic studies, this work focuses on the systematic methodology for developing, qualifying, and implementing hardfacing welding procedures in a production environment. The paper addresses the critical gap between laboratory research and shop-floor implementation, providing a framework that aligns with quality management systems and regulatory requirements.

Process Specification Development Methodology

The paper presents a comprehensive framework for hardfacing procedure development that follows a structured approach analogous to PDCA (Plan-Do-Check-Act) methodology:

Planning Phase

Define service conditions: temperature range, chemical environment, wear mechanism type (abrasive, adhesive, erosive, impact)
Select base material and substrate condition
Determine required hardness, thickness, and bond strength
Identify applicable standards: NB/T 47014, ASME IX, AWS D10.9, or enterprise specifications
Establish acceptance criteria for mechanical properties and NDT

Execution Phase

Develop welding procedure specification (WPS) including all essential and non-essential variables
Prepare procedure qualification record (PQR) with witness coupons
Perform metallographic examination, hardness testing, and wear testing
Conduct non-destructive testing (MT or PT for surface quality)

Verification Phase

Compare qualification results against acceptance criteria
Assess welder performance through operator qualification testing
Review process control parameters for reproducibility

Improvement Phase

Analyze field performance data
Update procedures based on lessons learned
Incorporate new consumable developments

Essential Variables and Process Control

The paper emphasizes the critical distinction between essential and non-essential variables in hardfacing procedures, which is fundamental to procedure qualification and transfer:

Variable Category	Parameter	Qualification Range	Impact if Exceeded
Essential	Consumable type/grade	Specific grade	Different metallurgy
Essential	Preheat temperature	±20°C from qualified	Cracking susceptibility
Essential	Interpass temperature	±20°C from qualified	Microstructure change
Essential	Number of passes	Same or fewer	Thermal history change
Essential	Electrode/dry time	As specified	Hydrogen cracking
Non-essential	Travel speed	±20%	Minor microstructure variation
Non-essential	Current polarity	As qualified	Minor dilution change
Non-essential	Nozzle stickout	±3 mm	Minor arc characteristics
Non-essential	Shielding gas flow	±25%	Minor oxidation effect

The study documents the qualification of multiple hardfacing processes including SMAW, SAW, and GMAW with various consumable types, demonstrating the importance of procedure-specific qualification rather than generic approach.

Application Cases and Quality Assurance

The paper presents several practical application cases from chemical equipment manufacturing, including hardfacing of pump impellers, valve seats, and heat exchanger tube sheets. A key finding is that the hardfacing process specification must integrate seamlessly with the parent component fabrication procedure. For pressure vessels governed by NB/T 47002 or ASME VIII Div.1, the hardfacing procedure must be qualified in accordance with the applicable code requirements and incorporated into the overall fabrication quality plan.

The quality assurance framework presented includes:

Material traceability for all hardfacing consumables
Environmental controls (humidity, temperature) for consumable storage
Welder qualification records with periodic requalification
In-process monitoring of critical parameters
Post-deposition inspection protocols including visual examination, magnetic particle testing, and hardness verification

Study Insights and Reflections

From a quality management perspective, this paper represents exactly the type of practical engineering guidance that bridges the gap between research publications and production reality. In my experience, the most common cause of hardfacing failures in production is not inadequate alloy selection but rather inadequate procedure qualification and process control. The systematic approach to WPS/PQR development documented here should serve as a model for all hardfacing operations. I particularly note the emphasis on consumable traceability and storage conditions—factors that are frequently neglected but can have dramatic effects on weld quality, particularly for hydrogen-sensitive nickel-based and cobalt-based hardfacing alloys. The integration of hardfacing procedures into the overall fabrication quality plan is essential for code compliance and should be mandatory in any facility manufacturing pressure equipment.