The calculations, tolerances and failure modes behind every drawing — for engineers who want to verify a spec themselves, not just take a supplier's word for it.
Organised in the order a design actually proceeds — from code and layout, through machining and finish, to what happens when something eventually goes wrong.
The single variable that connects hole layout to plate thickness. Simplified for illustration — always verify against the project-specific TEMA/ASME calculation.
Full mechanism, inspection method, and prevention detail live on the Failure Analysis page — this is the lookup table.
| Failure Mode | Typical Cause | First Sign | Primary Prevention |
|---|---|---|---|
| Pitting Corrosion | Chlorides on an insufficiently resistant material | Localized wall loss at hole ID | Upgrade material family (e.g. 316L → Duplex) |
| Crevice Corrosion | Stagnant fluid at tube-to-sheet joint | Attack concentrated at the joint, not open face | Full-depth expansion, weld-seal joints |
| Thermal Fatigue | Repeated startup/shutdown cycling | Cracking at ligaments under cyclic stress | Floating or U-tube design for high ΔT service |
| Erosion-Corrosion | High-velocity or two-phase flow at tube inlet | Localized thinning at tube entrance | Inlet tube liners, velocity limits at design stage |
| Galvanic Corrosion | Dissimilar metals in electrolyte contact | Accelerated attack on the less-noble metal | Compatible material pairing at design stage |
No. Ligament efficiency is a ratio describing how much material remains between adjacent holes at the weakest row. It's one input, alongside differential pressure, unsupported diameter, and allowable material stress, into the formula that calculates minimum required thickness. A tight ligament efficiency generally pushes required thickness up.
Only within limits. Adding tubes usually means tightening the pitch, which lowers ligament efficiency at the weakest row. Past a certain point the existing thickness will no longer satisfy the code calculation, meaning either a thicker plate or a larger-diameter sheet is required to hold the additional tubes safely.
Rougher surfaces provide more nucleation sites for pitting and make crevice corrosion more likely at the tube-to-sheet joint, since micro-crevices trap stagnant fluid. Hygienic and high-purity services in particular specify a minimum surface finish independent of the corrosion-resistance rating of the material itself.
A repair typically addresses individual failed tube-to-sheet joints — plugging, re-expanding, or re-welding specific holes — while re-tubing replaces the entire tube bundle. The tube sheet itself is reused in both cases unless it has also failed, which is a separate assessment covered on the Maintenance & Repair page.
Send your shell diameter, pitch, hole size and pressure class — NPRO India's engineering team will confirm the ligament efficiency and thickness before you finalize the order.
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