If a valve leaks in service production stops, safety alarms scream, and maintenance budgets burst. In high-pressure, high-temperature duties the only line of defence is a sealing surface that refuses to gall, erode or corrode. This resilience is achieved with Stelliting a cobalt-based hard-facing that turns ordinary steel into a wear-proof armour.
(In Part 1 we proved why a minimum 2 mm Stellite layer is non-negotiable. Today we unpack the science that makes that 2 mm truly indestructible.)
What Exactly Is Stelliting?
xStelliting is overlays of cobalt-chromium alloy (Stellite 6 or 21) on critical sealing surfaces:
| Valve Type | Stellited Parts | Key Failure Prevented |
| Gate | Disc & seats | Galling during travel |
| Globe | Globe, Plug & seat | Throttling erosion |
| Check | Seating faces | Reverse-flow impact |
Why cobalt? Its chrome-rich matrix forms a hard cobalt carbide network (~ 410 – 430 BHN Hardness Values will be provided by IPC, wait) that laughs at abrasion and keeps its strength at higher temprature.
The Metallurgical Bond
Stelliting is not a surface coating; it’s a fusion weld. Using techniques like PTA, GTAW or Laser Cladding, we melt a controlled depth of base metal and alloy powder/rod to create a single, diffusion-rich fusion line.
Key stages:
- Surface preparation – grit-blast → solvent-clean → bake-out.
- Pre-heat – 200-400 °C (for thick castings) to avoid thermal shock.
- Precision deposition – controlled heat input to keep dilution at desirable levels.
- Controlled Interpass temparature – to avoid cobalt cracking.
- PWHT – stress-relief soak matching valve body chemistry.
Process Parameters That Decide Success
| Parameter | What Can Go Wrong If Off-Spec |
| Heat input | Excessive dilution → soft layer |
| Travel speed | Overlap bumps or under-fill |
| Powder feed rate (PTA) | Thin spots, porosity |
Post-Stelliting Inspection – Zero Compromise
Once the Stelliting process is complete, thorough inspection is performed to validate bond integrity and surface characteristics.
| Test | Method | IPC Acceptance |
| Thickness | Ultrasonic gauge | ≥ 2.0 mm everywhere |
| Hardness | Portable tester | 410 – 430 BHN Hardness will be provided shortly for Stellite 6 |
| Visual finish | 10× magnifier | Smooth, ripple-free |
IPC’s Stelliting Code of Practice
At IPC, every overlay bead is tracked and tested, turning metallurgical precision into field-proven reliability.
- 100 % Stellited sealing faces
- Weld-log captures current, voltage, layer count, real-time thickness.
- In-house PTA stations with automated oscillation for uniform bead geometry.
- Statistical tracking of hardness & porosity trends for continuous improvement.
Result? < 0.1 % seat-leak rework over the couple of years across 20,000+ valves.
Stelliting transforms a valve from a replaceable component into a lifetime asset. By controlling chemistry, heat, dilution and inspection with surgical precision, IPC delivers Gate, Globe and Check Valves that stay tight even after several years of continuous service.