Hardfacing Wear-Resistant Layer on Shaft Kiln Feed Seal Pipe

Literature Overview

The paper by Li Guanghui, published in the journal Cement (2005, Issue 8, pp. 32), describes the application of hardfacing wear-resistant layers on the feed seal pipe of a Φ3m×11m shaft kiln in a cement production facility. This is a practical engineering case study addressing a specific wear problem in cement manufacturing equipment.

Application Background

Shaft kilns are traditional cement production equipment where raw materials are fed from the top and move downward through the kiln body under gravity. The feed seal pipe, also known as the feed lock pipe or feed seal device, is a critical component that prevents hot gases from escaping through the feed opening while allowing continuous material introduction. This component operates under severe conditions:

Operating Condition	Typical Value
Temperature	300-500°C
Abrasive particle size	0.5-5 mm
Material flow rate	50-150 t/h
Particle velocity	2-8 m/s
Service life requirement	12-24 months
Original material	Carbon steel (Q235 or similar)

Without protective measures, the feed seal pipe is subject to severe abrasive wear from cement raw materials containing silica, alumina, and other hard minerals. The wear pattern is typically localized at the throat section where material flow velocity is highest, leading to premature failure and unplanned downtime.

Hardfacing Solution and Process Design

The proposed solution involves hardfacing a wear-resistant alloy layer onto the inner surface of the feed seal pipe. The selection of hardfacing alloy and process parameters is guided by the following considerations:

Alloy selection: High-chromium cast iron or cobalt-based alloys are preferred for their excellent abrasion resistance. The alloy must withstand temperatures up to 500°C without significant softening or spalling.
Layer thickness: The hardfacing layer thickness is typically 3-8 mm, sufficient to provide extended service life while minimizing the risk of cracking or spalling. Excessive thickness increases residual stress and the likelihood of delamination.
Welding process: SMAW or FCAW is commonly employed for field application due to equipment portability and flexibility. The process allows welding in various positions, which is essential for cylindrical pipe geometry.
Preheating and interpass control: Preheating to 200-300°C is recommended to prevent cracking in the carbon steel substrate. Interpass temperature should be maintained below 250°C to control thermal stress accumulation.

Defect Analysis and Countermeasures

Based on engineering experience, the following defects and countermeasures are relevant:

Defect Type	Cause	Countermeasure
Cracking	High cooling rate, hydrogen embrittlement	Preheating, low-hydrogen electrodes, controlled cooling
Spalling	Excessive residual stress, thick layers	Reduce layer thickness, stress relief, controlled cooling
Porosity	Surface contamination, improper shielding	Surface cleaning, proper gas flow, controlled parameters
Poor bonding	Inadequate surface preparation	Grinding to bare metal, solvent cleaning

Engineering Practice and Results

The hardfaced feed seal pipe demonstrated significantly improved service life compared to unprotected pipes. Field data indicates that the hardfaced pipe achieved a service life of 18-24 months, compared to 6-9 months for the original unprotected pipe. This represents a 2-3 times improvement in service life, translating into substantial reduction in maintenance downtime and replacement costs.

The economic analysis shows that the hardfacing process cost is significantly lower than the cost of manufacturing a new pipe from wear-resistant material. Furthermore, the hardfacing process can be performed in the field without removing the pipe from service, minimizing production disruption.

Study Insights

This paper exemplifies the practical application of hardfacing technology in addressing a specific industrial wear problem. The key insight is that hardfacing is not merely a surface treatment but a strategic maintenance solution that balances performance, cost, and operational continuity.

For engineers in the cement industry, this case study demonstrates that even simple components such as feed seal pipes can benefit significantly from proper hardfacing design and execution. The selection of appropriate alloy composition, layer thickness, and welding parameters is critical to achieving the desired service life improvement.

The paper also highlights the importance of field applicability in hardfacing technology selection. Unlike laboratory conditions, field welding must accommodate environmental constraints, equipment limitations, and operator skill levels. Process flexibility and robustness are as important as metallurgical performance in practical applications.