NDT for Hot-Gas-Path Parts: What the Release Pack Must Show

NDT means non-destructive testing. Euroturbine writes the plan against the component, not against a generic turbine checklist. A hot-gas-path part is released when four inspections have each made a decision: FPI on the surface, X-ray on the casting, CMM on the stack, and a wall map where the duty is a liner or a thin duct. Those four results are written below. A photograph of a clean part is not any of them.

FPI is fluorescent penetrant inspection. Dye finds a crack that breaks the surface — leading-edge, trailing-edge, platform, fir-tree faces that you can wet. It does not see a void in the middle of a casting. Euroturbine will not release a first-stage blade or vane on FPI alone. A clean FPI on a hollow 9E bucket is one sentence. The next sentence is still X-ray.

Case. A V94.2 first-stage vane comes back from strip. FPI is clean. The plant asks to coat and ship. Euroturbine still runs volumetric inspection. A porosity cluster sits under a clean surface. That vane is not result 1 pass-and-forget. It is a HIP or scrap conversation. HIP means hot isostatic pressing. FPI had nothing to say about that cluster.

X-ray — or an agreed volumetric equivalent — looks through the metal. On investment-cast first-stage hardware that is the decision for internal voids, shrink, and inclusions the dye cannot reach. Acceptance is against a written class, not against “به نظر خوب می‌آید”. The inspector level sits on the certificate next to the heat number. Repair hardware is mapped against the repair spec, then the restored zone is often X-rayed again before recoating.

Case. A new-make 9E first-stage bucket. FPI is clean. X-ray shows a void in the airfoil wall inside the HIP envelope, remaining wall still enough. Euroturbine writes HIP plus recoat, not ship-as-cast. If the void sits in a thin wall below the minimum, the decision is scrap that serial. X-ray is what split those two sentences. A sales PDF that says “NDT انجام شد” without the method and class is not result 2.

CMM is a coordinate measuring machine. It decides interchangeability: airfoil, root, throat, seal lands. A part that passed FPI and X-ray can still be fat in the throat or out on the fir-tree. That part will not drop in. Euroturbine puts a CMM extract in the same pack as the NDT sheets. Transition pieces need the duct and the seal lands measured, not only a photograph of the shell.

Case. An SGT-600 power-turbine blade, repair complete, NDT clean. CMM shows the root off the disk stack. Shipping it would have meant dressing on site or a vibration trip. Euroturbine holds the serial. Result 3 failed. Results 1 and 2 had passed. That is why the pack has three sheets, not one stamp.

Combustion liners and thin transition ducts add wall-thickness mapping. FPI finds a crack at a cross-fire boss. It does not tell you the remaining millimetres next to that crack. A visual “it still looks round” is not an accept criterion. The wall map decides repair, a limited restore, or new-make. Bearings follow a different magnetic or ultrasonic route; they are not this result.

Case. A 9E liner set, flame face still coated. FPI shows a short indication at a cross-fire boss. The wall map next to that indication is below the repair minimum. Euroturbine writes new-make for that serial, not blend-and-hope. Another liner in the same crate has a clean wall and tired TBC — thermal barrier coating — and goes to strip and recoat. The wall map split the crate. The word “لاینر” did not.

Send the OEM part number — the original manufacturer number — and whether the set is new-make or repair. Euroturbine returns the inspection plan with the quote: which of the four results apply to that line. The plan does not arrive after the boxes. AOG — a unit that cannot start — still keeps these four results. Fast is not the same as uninspected.