Cladding of Pulverized Coal Slurry Pressurized Gasifier Nozzles

Literature Overview and Operating Conditions

This 1998 publication by Yang Shanglai and Zhang Wenhong from Shandong Lunan Chemical Industry Group Company addresses the cladding of nozzles used in pulverized coal slurry pressurized gasifiers. Published in Welding Technology journal, this work addresses one of the most demanding wear environments in the chemical industry — the gasification of coal slurry under high pressure and temperature conditions.

Extreme Service Environment Analysis

Pulverized coal slurry pressurized gasifiers operate under conditions that are extremely harsh for nozzle materials:

Operating Parameter	Typical Value	Challenge
Operating temperature	1100-1400°C	High-temperature oxidation
Operating pressure	2.0-4.5 MPa	High mechanical stress
Slurry composition	Coal + water + additives	Abrasive + erosive
Flow velocity at nozzle	30-80 m/s	High-velocity erosion
Slurry particle size	50-150 μm	Abrasive wear
Service environment	Reducing atmosphere	Sulfur and chlorine attack
Expected service life	3000-8000 hours	Frequent maintenance

The nozzle experiences a combination of abrasive wear from coal particles, erosive wear from high-velocity slurry flow, thermal degradation from high operating temperatures, and chemical attack from sulfur and chlorine compounds in the coal. This multi-mechanism wear environment demands overlay materials with exceptional multi-property performance.

Overlay Material Selection and Process Design

The authors evaluated several overlay material systems for gasifier nozzle application:

Material System Comparison

Material System	Composition	Hardness	Temperature Resistance	Abrasive Resistance	Cost
Cr-C high-carbon	Cr18C4, Cr25C3	60-65 HRC	<800°C	Excellent	Low
Ni-Cr	Ni-20Cr-4C	45-55 HRC	<1000°C	Good	Medium
Co-Cr	Stellite 6 (Co-Cr-W)	40-50 HRC	<1100°C	Excellent	High
Ni-based	Inconel 625	30-35 HRC	<1100°C	Moderate	Very High
Composite	Cr-C + Ni-Cr layered	50-60 HRC	<900°C	Excellent	Medium-High

Based on the comprehensive evaluation, the authors recommended a composite overlay approach combining a Ni-Cr transition layer with a Cr-C hardfacing surface layer. This design provided:

Transition layer (Ni-Cr): Excellent adhesion to the base material, good resistance to thermal cracking, and moderate wear resistance
Surface layer (Cr-C): High hardness for abrasive resistance, with acceptable performance at operating temperatures

Welding Process Parameters

The overlay was applied using submerged arc welding (SAW) with the following parameters:

Parameter	Transition Layer	Surface Layer
Consumable	Ni-based wire + flux	Cr-C hardfacing wire
Flux type	HJ431 (basic)	HJ431 (basic)
Welding current	280-350 A	300-380 A
Arc voltage	28-32 V	30-35 V
Travel speed	120-180 mm/min	100-150 mm/min
Layer thickness	2-3 mm	3-5 mm
Interpass temperature	200-300°C	150-250°C

The nozzle geometry presented specific challenges for overlay application. The internal channel of the nozzle required special attention to ensure uniform coverage and avoid distortion of the flow passage. The authors recommended using backing bars and careful travel technique to maintain dimensional accuracy of the nozzle bore.

Performance Testing and Service Evaluation

The authors conducted extensive testing to validate the overlay design:

Laboratory Testing

Test Method	Results	Acceptance Criteria
Hardness (surface)	58-62 HRC	≥55 HRC
Hardness (transition)	42-48 HRC	≥35 HRC
Wear test (slurry)	12000 cycles	≥8000 cycles
Thermal cycling	50 cycles (25-1200°C)	No cracking
Bond strength	320 MPa	≥250 MPa
Corrosion (H2S)	168 h, no pitting	No penetration

Field Service Performance

The authors reported field service data from gasifier operations:

Service Condition	Average Life	Wear Rate	Primary Failure Mode
Normal operation	5000-7000 h	0.05-0.08 mm/1000h	Gradual erosion
High-load operation	3000-4500 h	0.10-0.15 mm/1000h	Accelerated erosion
Poor slurry quality	1500-2500 h	0.20-0.30 mm/1000h	Abrasive + chemical

Study Insights and Engineering Recommendations

This literature provides valuable insight into the cladding of components operating under extreme multi-mechanism wear conditions. The authors' approach of combining transition and surface layers represents a sophisticated engineering solution that addresses the fundamental challenge of achieving both adhesion and wear resistance in a single overlay design.

A key insight from this work is the importance of understanding the specific wear mechanisms operating in the service environment. The gasifier nozzle experiences a complex combination of abrasive, erosive, thermal, and chemical degradation mechanisms, and no single overlay material can optimally address all of these simultaneously. The layered approach allows each layer to be optimized for its specific role — the transition layer for adhesion and thermal stability, and the surface layer for wear resistance.

The authors also emphasized the importance of process control during overlay application, particularly for nozzles with internal channels. Distortion of the flow passage during welding can significantly impact gasifier performance and must be carefully managed through controlled heat input, symmetric welding sequences, and post-weld machining verification.

This work remains highly relevant for contemporary gasification technology, as the operating conditions continue to intensify with the development of more efficient gasification systems. The principles established in this study — material selection based on wear mechanism analysis, layered overlay design for multi-property requirements, and rigorous quality control — form the foundation for modern gasifier nozzle maintenance practices.

Concluding Reflections on the Collection of Studies

These five publications, spanning from 1994 to 2002, collectively represent a rich body of practical knowledge in the field of weld overlay and cladding technology across diverse industrial applications. From mining rolling rolls to ceramic tile molds, from coal grinding mills to cold rolling equipment and gasification nozzles, each study addresses the fundamental engineering challenge of extending component life through surface engineering. The common thread across all five works is the recognition that successful overlay welding requires a holistic approach — understanding the service environment, selecting appropriate materials, controlling process parameters, and implementing rigorous quality assurance. These studies, while published over two decades ago, continue to provide valuable guidance for contemporary engineers, as the fundamental principles of metallurgy, welding, and wear engineering remain unchanged despite advances in equipment and technology. The practical wisdom contained in these publications — particularly regarding interface management, residual stress control, and multi-layer overlay design — remains essential knowledge for anyone engaged in cladding and surface engineering work.