Hardfacing Welding Procedure Specification Compilation Evaluation and Application According to ASME Code

Literature Overview

This paper by Liu Yuan and colleagues from Dalian Hitachi Machinery Equipment Co., Ltd., published in Chemical Equipment Technology (Volume 32, Issue 1, 2011, pp. 28-34), presents a practical case study of hardfacing welding procedure specification (WPS) development for pressure vessel components in accordance with ASME Boiler and Pressure Vessel Code Section IX. The paper bridges the gap between theoretical welding science and regulatory compliance requirements for hardfacing operations in the chemical equipment manufacturing industry.

Core Technical Content

The paper addresses several critical aspects of ASME Code-compliant hardfacing:

WPS development and documentation requirements
Welding procedure qualification (WPQ) testing protocols
Acceptance criteria for hardfacing overlay welds
Application considerations for pressure vessel components

ASME Section IX Requirements for Hardfacing

According to ASME Section IX, Part Q (Welding, Brazing, and Fusing Qualifications), hardfacing welding requires qualification under specific rules that differ from conventional structural welding:

Hardfacing is classified as a separate welding process requiring its own qualification
Qualification must demonstrate both weldability (crack-free deposition) and functional performance (hardness, wear resistance)
The WPS must specify all essential variables that could affect the hardfacing deposit properties
Multiple layers may require qualification of both the first layer (for base metal compatibility) and subsequent layers (for deposit properties)

Process Qualification Analysis

Essential Variables for Hardfacing WPS

Variable Category	Specific Variable	Qualification Range
Welding process	PTAW, SMAW, SAW, FCAW	Process type must match
Base metal group	P-No. classification	Must cover actual base metal
Filler metal	A-No. classification for hardfacing	Must match WPS
Preheat temperature	Minimum/maximum	Typically 50-250°C depending on base metal
Interpass temperature	Maximum limit	Usually not to exceed 300°C
Current/voltage	±10% or ±15% range	Depends on process
Travel speed	±15% range	Affects dilution
Layer thickness	Maximum qualification	Typically 6.35 mm per layer
Post-weld heat treatment	Type and temperature	If used in WPS, must be qualified

Qualification Testing Requirements

The ASME Code requires the following tests for hardfacing qualification:

Visual examination - All surfaces must be free from cracks, excessive undercut, and porosity
Hardness testing - Surface hardness must meet specified minimum requirements for the hardfacing alloy
Metallographic examination - Cross-section examination of the first layer to verify:

No cracks at the base metal/weld interface
No excessive fusion into the base metal (typically not exceeding 3 mm or as specified)
Sound weld fusion

Wear testing - May be required for critical applications

Engineering Practice Case

The paper describes a specific pressure vessel component hardfacing application at Dalian Hitachi Machinery, which manufactures chemical processing equipment. Key engineering considerations include:

Base metal compatibility: Pressure vessel steels (typically P-No. 1 carbon steel or P-No. 3 low-alloy steel) may require careful control of dilution to prevent cracking in the hardfacing layer
Residual stress management: Hardfacing deposits create significant residual stresses due to differential thermal contraction between the hardfacing alloy and base metal
Code documentation: Complete traceability of materials, procedures, and personnel qualifications
Production reproducibility: The qualified WPS must be applicable across production volumes, not just laboratory conditions

Common Defects and Countermeasures

Defect Type	Root Cause	Prevention/Countermeasure
Cracking at interface	Excessive dilution, high base metal carbon equivalent	Limit first layer thickness, use transition layer, preheat
Porosity	Hydrogen absorption, poor shielding	Dry electrode storage, adequate gas coverage, low travel speed
Excessive fusion	High current, slow travel speed	Reduce heat input, increase travel speed
Hardness not meeting specification	Excessive dilution, improper cooling rate	Use multiple thin layers, optimize heat input
Undercut	Incorrect torch angle, excessive travel speed	Adjust technique, reduce travel speed

Standards Comparison

Standard	Scope	Hardfacing Requirements
ASME Sec. IX Part Q	Pressure vessels	Qualification required, hardness and microstructure testing
AWS D10.9	Hardfacing general	Classification and qualification of hardfacing processes
API 16C	Pipeline hardfacing	Specific for pipeline repair hardfacing
ISO 14732	Hardfacing qualification	International equivalent to AWS D10.9
GB/T 985	Chinese hardfacing	Chinese national standard for hardfacing procedures

Key Questions and Reflections

The paper highlights a practical challenge that many engineers face: translating ASME Code requirements into executable production procedures. Several critical points deserve emphasis:

The distinction between hardfacing qualification and structural welding qualification is often misunderstood, leading to non-compliant procedures
The "hardness requirement" in ASME Code is often interpreted as a minimum surface hardness, but depth-dependent hardness profiles are more informative for wear applications
The code does not explicitly require wear testing for qualification, but for critical applications, supplementary wear testing is strongly recommended
The transition layer concept (using a compatible alloy between base metal and hardfacing) is not always mandated by code but is essential engineering practice for preventing interface cracking

Study Insights and Implications

This paper serves as an excellent practical guide for engineers who must develop code-compliant hardfacing procedures. The key takeaway is that hardfacing qualification is not merely a formality but a systematic process that ensures the deposit will perform reliably in service. For chemical equipment manufacturers subject to ASME code requirements, understanding the interplay between qualification variables, deposit properties, and service conditions is essential for producing compliant and reliable hardfacing work.