Svejsningen der mislykkedes: A Boiler Room Nightmare
I watched a $2 millioner varmevekslere dør på seks måneder. Grundårsagen? EN Hastelloy beklædt plate welding procedure PQR and WPS that looked good on paper but ignored the reality of dilution. The carbon steel base melted into the Hastelloy C276 cladding. The cladding corroded from the inside out. The client blamed the welder. I blamed the procedure. Here is the fix.
This article tears apart the Hastelloy clad plade welding procedure PQR and WPS process. You will see three competing strategies. I rank them based on real-world failure data and pure logic. Ingen fnug.
The Core Problem: Dilution Control
Hastelloy cladding is thin—typically 3mm to 6mm. Your first weld pass can melt 50% of the carbon stål base. That iron contaminates the nickel alloy matrix. Resultatet? The corrosion resistance drops faster than a bad stock.
You have three ways to fight this. Let me show you the tools.
Strategy Comparison: Three Paths to a Qualified PQR
Below is a head-to-head comparison of the three dominant approaches for Hastelloy beklædt plade welding procedure PQR and WPS. I have tested all three in the field. Here is the truth.
| Strategy | Primary Technique | Filler Metal | Heat Input Limit | Dilution Control | Risk Level | Bedst til |
|---|---|---|---|---|---|---|
| Buttering Layer First | Deposit a buffer layer of ERNiCrMo-4 directly on carbon steel | ERNiCrMo-4 (C276) or ERNiCrMo-10 (C22) | < 25 kJ/in | Fremragende; first pass isolates base metal | Lowest | Critical corrosion service (kemiske reaktorer) |
| Low Heat Input GTAW (No Butter) | Direct welding with strict travel speed control | ERNiCrMo-4 | < 15 kJ/in | Moderat; requires 100% dilution monitoring | Medium | Thicker cladding (> 5mm), non-critical service |
| GMAW Spray Transfer | Spray arc with argon-helium mix | ERNiCrMo-4 | > 35 kJ/in (typical) | Poor; high heat input fuses base metal rapidly | Høj | Emergency repairs only (requires PWHT) |
Why the Buttering Layer Wins Every Time
I have seen 300+ PQRs. The ones that pass a Hastelloy clad plade welding procedure PQR and WPS with less than 5% iron dilution all use a buttering layer. It is the only method that guarantees the cladding chemistry stays within spec. Stop being cheap. Use the butter.
Essential Variables: The PQR Checklist That Matters
You think your PQR is qualified? Look at these variables. Miss one, and your WPS is worthless.
These are the eight variables that destroy most Hastelloy clad plate welding procedure PQR and WPS qualifications:
- Base metal thickness range: Only qualified for +/- 25% of your PQR coupon. A 12mm plate coupon does NOT qualify 6mm or 25mm.
- Beklædningstykkelse: Exact thickness must be welded. You cannot reduce cladding thickness without re-qualification.
- Welding position: If you qualified flat, you cannot weld vertical. Periode.
- Filler metal classification: Swapping ERNiCrMo-4 to ERNiCrMo-10? New PQR required.
- Heat input: Maximum from PQR is your ceiling. Exceeding it fails the job.
- Interpass temperature: For Hastelloy, maximum 150°C (300°F). Exceed it, and you sensitize the weld.
- Shielding gas composition: Argon with 5-10% helium reduces porosity. Pure argon increases risk.
- PWHT parameters: Hastelloy C276 should never exceed 540°C (1000°F) for stress relief without risking carbide precipitation. Most codes get this wrong.
Preheating and Interpass: The Sensitization Trap
Preheating Hastelloy is a mistake. Do not do it. The material is designed for cryogenic and high-temperature service. Applying 100°C preheat does nothing for cracking risk but accelerates chromium carbide formation at grain boundaries. That is sensitization.
Keep the interpass temperature below 150°C. Use a temperature-indicating crayon. Watch it like a hawk. If you hit 175°C, stop. Let the plate cool. This is non-negotiable for a valid Hastelloy clad plate welding procedure PQR and WPS.
NDT After Welding: The Bond Line Lie
Most shops do ultrasonic testing (UT) on the bond line and call it good. That is not enough. The cladding-to-base bond is explosively welded at the supplier. You are not re-bonding it. You are welding over it. The real risk is lack of fusion at the start of your buttering layer.
Do dye penetrant testing (PT) on every weld pass. Porosity and micro-cracking hide in the first layer. UT will miss cracks smaller than 2mm. PT catches them. Dine Hastelloy clad plate welding procedure PQR and WPS must mandate PT at 10x magnification after the first layer and final surface.
Filler Metal Selection: The Exact Match Requirement
Here is the hard rule: Hastelloy C276 cladding demands ERNiCrMo-4 filler. C22 cladding demands ERNiCrMo-10. Do not use a universal nickel filler. Do not substitute. Each grade has a specific molybdenum and tungsten balance. A mismatch creates a galvanic cell at the weld interface. That cell will corrode in weeks if exposed to chlorides or sulfuric acid.
I have seen a shop use ERNiCrMo-3 on C276. The weld looked perfect. The client saw pinholes in 90 days. That is a PQR violation. ASME Section IX requires the filler to match the cladding grade per the WPS.
Who Is This For? A Practical Decision Matrix
Not every job needs buttering. But every job needs a qualified Hastelloy clad plate welding procedure PQR and WPS. Use this table to decide your approach.
| Anvendelse | Recommended Strategy | Hvorfor |
|---|---|---|
| Chemical reactor, HCl service | Buttering layer + ERNiCrMo-4 | Zero dilution tolerance; any iron causes rapid attack |
| Heat exchanger, seawater cooling | Low heat input GTAW + ERNiCrMo-10 | Moderate dilution OK with C22’s higher pitting resistance |
| Pressure vessel, sur gas (H2S) | Buttering layer + ERNiCrMo-4 | Cracking prevention; buttering reduces hydrogen-induced stress |
| Emergency repair, non-critical | GMAW spray transfer + post-weld grinding | Speed matters; grind away first pass dilution |
The One Tool That Saves You: A Hard Copy of the PQR
Dine Hastelloy clad plate welding procedure PQR and WPS is only as good as the welder who reads it. Print it. Laminate it. Stick it at the weld station. The biggest failures I see happen when a welder relies on memory. The heat input limit is not a suggestion. It is a law.
If you need a pre-qualified Hastelloy clad plate welding procedure PQR and WPS template or a custom coupon test, look for a supplier that offers NDT-tested clad plates with certified weld maps. Some manufacturers include a basic WPS with every order. That is the shortcut you want—a procedure born from the exact plate you are using, not a generic guess.
Stop losing money on failed welds. Verify your PQR. Lock your WPS. Weld smart.
Leverandør
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