How a Compressor Blade Differs from a Hot-Gas-Path Blade

If you walk the compressor of a heavy-duty machine you see rows of relatively stout airfoils. The metal is usually a high-strength stainless steel, a titanium alloy, or a nickel alloy chosen for strength and corrosion, not for a thousand-degree gas. Large compressor blades are often machined from a forged preform so the grain follows the airfoil. Smaller ones come from bar or billet. They do not receive a ceramic thermal barrier coating — TBC in every shop — because the gas there is not hot enough to need one. What they do see is sand, salt, wash water and the occasional foreign object. That is a different life from a first-stage bucket.

This is the job when the part lives in the cold or warm compressor: an inlet guide vane — IGV in every Iranian shop — a variable or fixed stator, or a rotor blade. The useful request names that row, not only the word پره. The metal is a machining alloy. Failure is erosion, a nick from a foreign object, a rub after a stall, or corrosion under deposits. Creep at metal temperatures near 1000 °C is not the story. A shop that only mills stainless airfoils is real. It is not a substitute for a vacuum-cast, coated first-stage turbine blade.

Case A. An SGT-600 station on a gas line sends a photograph labelled پره توربین. The airfoil is stout, uncoated, and the root is a compressor dovetail, not a fir-tree into a hot disc. Euroturbine writes compressor rotor blade, not hot-gas-path. We will reverse-engineer that row if you send a sample and the original-equipment number — OEM in every store. We will not price it as a first-stage bucket.

Hot gas path, often shortened to HGP, is the section after the combustor: first-stage nozzles, rotating blades, later stages, shrouds. A first-stage turbine blade is usually vacuum investment-cast from a nickel superalloy in the IN738, GTD111 or Rene 80 family. The root is then machined to the disc serration. Most rows take a metallic bond coat such as MCrAlY, and many take a ceramic TBC. The blade sees combustion gas, centrifugal load and oxidation. When a plant searches پره توربین گازی for an overhaul, this is usually the part they mean, unless they have written کمپرسور on the form.

Case B. A combined-cycle unit on Frame 9E opens a hot-gas-path outage. The shopping list is first-stage buckets, OEM numbers on the last outage report, quantity for a full row, hours and starts on that machine, and a note: new-make unless remaining wall allows a written repair. Euroturbine prices that as HGP. A compressor IGV from the same unit stays on a different line and a different shop conversation.

A compressor blade that has taken a stone looks ugly and may be blended or replaced. The metal underneath is still a machining alloy. A hot-gas-path blade that has lost coating, opened a cooling hole or grown by creep is a metallurgical case. You cannot judge it by the same eye you use on a compressor nick. Dimensional inspection on a coordinate measuring machine — CMM in every Iranian shop — uses different programmes for the two families. Root geometry, stacking and coating-thickness allowance are not interchangeable. Asking one programme to serve both is how a fitted blade still rubs.

Case C. The same V94.2 combined-cycle unit sends two photographs in one email. One is a compressor stator with a foreign-object nick; remaining wall is enough to blend. The other is a first-stage turbine vane with TBC gone and a cooling hole opened. Euroturbine writes blend-and-inspect on the compressor vane, and strip-recoat or replace on the HGP vane. One CMM programme is not used for both.

A request Euroturbine can price without sending the list back looks like this. Nameplate: SGT-600 station, or Frame 9E combined-cycle — write the plate you have. Section: compressor or turbine. Row: IGV / stator / rotor, or HGP stage 1 rotating. OEM number from the last outage report, not a nickname. Quantity: one sample, or a full row. Hours and starts on that machine. Job: new-make, repair, or reverse-engineering if you are sending a compressor sample. Photographs: root and both sides of the airfoil, not an airfoil from ten metres. If the part has already run, attach the last coating record and the last non-destructive test — NDT in every shop.

Euroturbine manufactures and inspects hot-gas-path blades and vanes. A compressor airfoil is a separate request unless you send a sample and ask for reverse engineering. We will say the job is in scope, or we will point the enquiry. We will not price a compressor job as if it were a first-stage bucket.

Blade versus vane · Hot-gas-path parts by frame · Send photographs