Views: 0 Author: Site Editor Publish Time: 2026-10-30 Origin: Site
The seal comes back for rebuild, sleeve gland and springs all 316 as usual. Someone wrote on the work order, go 2205 duplex this time. Half those lines get ticked out of habit. The metal is worth the premium only when the fluid actually ate the last one. Fail it by wear, by a cracked face, by a sloppy fit, and the dearer alloy is just dead weight in the bill.
316L is what gets used unless someone says otherwise. Cheap, machines and welds without drama, and it covers most of what a seal sees, plain water, mild acid, the ordinary plant fluids. 2205 duplex costs more and fights back in the shop, but throw it at salty water and it just takes it. Seawater, brackish, warm and chlorinated, that is where 316L starts to grow pits and then cracks. The difference shows up as a number, PREN, a rough corrosion score, 316L around 25, 2205 around 35. The wider that gap, the better it sits in brine.
Read the old sleeve or gland. Pits in it, or a stress crack running from chloride, that is the case for 2205. 316L starts to go above roughly 1000 ppm warm chloride, or in seawater past about 25 degrees C, and the cracking worsens past 60 degrees C. 2205 carries that load to about 75 to 100 degrees C and shrugs off chloride levels that would kill 316L. The spring is the part that usually goes first, smallest section, most stress, and a duplex sleeve does nothing for it. Where the spring is the weak link the answer is a Hastelloy C-276 or Inconel spring, not a fancier sleeve.
Duplex is out of its window cold, down in cryogenic service, and above about 300 degrees C where it turns brittle. Standard 316L hardware runs fine in clean ambient water, a low-chloride acid line, indoor kit with no real corrosion path. Spending on 2205 there is money on the shelf. The grade above it, super duplex 2507, only earns its far higher price where 2205 is already at the edge, hot high-chloride seawater or sour hydrogen sulfide service.
None of the usual killers care what the hardware is made of, dry running, a shattered ceramic face, a sloppy fit, vibration, grit in the fluid. They would destroy a 2507 just as fast. Open the failure report before the grade changes, chloride level, temperature, pH, any hydrogen sulfide or carbon dioxide, flow speed. If the last seal died of wear or fit, the dearer sleeve is the same failure with a shinier label.
2205 welds in a narrow band. Hand it to a shop that only knows 316L and the part comes back weaker, the weld ate the balance out of the steel. It also sits more noble than the carbon steel shaft beside it, so it pushes the corrosion onto that cheaper neighbour. Write 2205 on the order and the welding procedure and the mating metals have to be on there too, or the upgrade is a word on paper.
FBU builds the seal to the chamber and the fluid it sees, not to whatever the nameplate says. The seal's own metal, sleeve gland springs, gets matched the same way. Send the duty in. What comes back fits the service, not just the drawing.
Grade | Corrosion score, PREN | Holds up to | Where it struggles | Pick it when |
|---|---|---|---|---|
316L, CF8M cast or 316SS wrought | about 25 | Limited in warm seawater | Cracks above 60 degrees C chloride stress, brittle when very cold or above 300 degrees C | Cold, clean, low-chloride duty |
2205 duplex, A890 Grade 4A | about 35 | Tens of thousands ppm chloride, 75 to 100 degrees C stress cracking | Above 300 degrees C, cryogenic | Warm chloride, seawater, erosive slurry |
2507 super duplex, A890 Grade 6A | above 42 | Permanent seawater immersion | Very high cost | Hot high-chloride seawater, sour H2S service |
Should the seal's metal hardware be upgraded from 316 stainless to duplex when the seal is replaced?
Only when the last metal actually corroded. If the old sleeve or gland pitted in warm chloride, or cracked from chloride stress above 60 degrees C, 2205 is the answer. If the seal failed from wear, thermal shock, vibration or bad installation, dearer hardware just relabels the same failure. The grade should be set only after the chloride level, temperature, pH, any hydrogen sulfide or carbon dioxide, and flow speed are checked.
What is the difference between 316 and 2205 duplex for seal hardware?
316L is the cheap, easy default with a corrosion score near 25. 2205 duplex costs more and is harder to weld, but its score near 35 lets it shrug off salty, chloride-rich water that pits and cracks 316L. On a seal the parts are small, so the reason to change grade is corrosion on the wetted metal, not strength or wall thickness. The score, called PREN, is what decides chloride service.
When does duplex stainless not worth the upgrade on a seal?
In cold or cryogenic duty, above about 300 degrees C where 2205 embrittles, and in clean low-chloride fresh water or mild indoor service where 316L already lasts. The spring usually corrodes first and the real fix there is often a Hastelloy C-276 or Inconel spring rather than a duplex sleeve. 2205 also needs a qualified weld procedure and, being more noble, can drive corrosion onto the carbon steel it meets, so the mating metals and the procedure must be specified too.