Wear-Resistant Cladding Surfacing on Large Gas Cylinder Compressor Plungers

Industrial Application and Failure Analysis

The paper by Zhang Junlin, Wang Junlin, and Chen Zhuohua from Taiyuan Heavy Machinery Works, published in the journal Welding in 1990, addresses the wear problem encountered on the main and auxiliary working plungers of large gas cylinder compressors. These plungers operate under extreme conditions: high contact pressure from reciprocating motion, sliding friction against cylinder liners, potential corrosive attack from compressed gas media, and thermal cycling from adiabatic compression and expansion. The primary failure mode is adhesive and abrasive wear at the plunger surface, which leads to increased clearance, reduced compression efficiency, elevated leakage, and ultimately unplanned downtime.

The original plunger material, typically a medium-carbon steel or low-alloy steel, provides adequate strength but insufficient surface hardness and wear resistance for the demanding operating conditions. The solution adopted is a hardfacing overlay applied to the critical sliding surfaces, creating a bimetallic plunger with a tough core and a wear-resistant surface layer.

Surfacing Process and Consumable Selection

The surfacing process employed is submerged arc welding (SAW) or flux-cored arc welding (FCAW), chosen for their high deposition rates and deep penetration capabilities suitable for thick plunger sections. The consumable selection is guided by the tribological requirements of the application:

Consumable Type	Hardness (HV)	Key Alloying Elements	Wear Mechanism Resistance
High-carbon steel hardfacing	400–550	C, Cr, Mn	Abrasive wear
Medium-alloy steel hardfacing	300–450	Cr, Mo, V	Adhesive + abrasive wear
Stellite-type alloy	350–500	Cr, Co, W, C	Abrasive + corrosion wear
High-silicon alloy	300–400	Si, Mn	Abrasive wear (slurry)

For the gas cylinder compressor plungers, a high-carbon chromium-molybdenum hardfacing alloy was selected, providing a balance of hardness, toughness, and resistance to both abrasive and adhesive wear. The overlay thickness was designed at 3–5 mm to ensure adequate wear life while avoiding excessive distortion of the plunger geometry.

Microstructure and Wear Performance

The microstructure of the hardfacing overlay consists of martensitic matrix with dispersed carbides of type M7C3 and M23C6, where M represents Cr, Mo, and Fe. The carbide network provides the primary wear resistance mechanism by resisting micro-ploughing and micro-cutting by abrasive particles. The martensitic matrix contributes to the overall hardness and provides the ductile phase that accommodates cyclic loading without catastrophic cracking.

The hardness profile across the overlay cross-section shows a gradient from approximately 500 HV at the surface to 350 HV near the fusion boundary, with a rapid drop to 200 HV in the base metal. This gradient is beneficial because it provides a smooth transition in mechanical properties that reduces stress concentration at the overlay-base metal interface.

Test Condition	Original Plunger (mm wear)	Surfaced Plunger (mm wear)	Wear Life Improvement
500 hours, dry sliding	0.85	0.15	5.7×
1000 hours, dry sliding	1.70	0.28	6.1×
500 hours, with gas media	1.20	0.22	5.5×

Quality Control and Defect Prevention

The surfacing process is susceptible to several defect types that must be actively controlled. Cracking in the hardfacing overlay is the most common defect, caused by the high carbon content and rapid cooling rate that promote brittle martensitic transformation with high residual tensile stress. Countermeasures include preheating the base metal to 200–300°C, using a low-heat-input welding sequence, and applying post-weld heat treatment (PWHT) at 550–650°C to temper the martensite and relieve residual stresses.

Porosity in the overlay can result from moisture contamination of the flux or wire, inadequate flux coverage, or excessive arc voltage. Prevention requires strict flux drying procedures (300°C for 2 hours minimum), proper flux coverage geometry, and controlled arc parameters. Lack of fusion at the overlay-base metal interface is another critical defect that compromises the bond strength and can lead to overlay spallation during service. Ensuring adequate penetration into the base metal through proper current settings and proper surface preparation (grinding to bare metal within a 5 mm width on each side of the weld) is essential.

Study Insights and Practical Recommendations

This 1990 study remains relevant for engineers dealing with wear problems in reciprocating compressor components. The key insight is that the selection of hardfacing alloy must be matched not only to the wear mechanism but also to the thermal and mechanical loading conditions of the specific application. A harder overlay is not always better; excessive hardness can lead to cracking under thermal cycling or impact loading. The optimal overlay design balances hardness, toughness, and thermal stability. Engineers should always perform tribological testing under conditions that simulate actual service before committing to a production surfacing specification.