Caustic SCC of SS316L

[shvet]

Hello, forum

We are purchasing a plate heat exchanger (API 662-1) for water-water service. Materials of construction: plates 316L, shell CS. For hot side there is a short-term warm 15%w caustic case with risk of overheating up to 90°C which to be considered. Vendor does not want to provide PWHT for hot side and insists on 316L or A321 lining/cladding. Para. 4.5.3.6.b API 571-2011 states "300 Series SS offer little advantage in resistance to cracking over CS".

Can anyone share a worth source for CSCC of SS300?

 

[XL83NL]

API 682 is for Pumps—Shaft Sealing Systems for Centrifugal and Rotary Pumps
I think you meant API 662 (ISO 15547-1), Plate Heat Exchangers for General Refinery Services—Part 1—Plate-and-Frame Heat Exchangers?

Huub
- You never get what you expect, you only get what you inspect.

 

[shvet]

Sure, API 662-1 / ISO 15547-1.

 

[0707]

IMO CS above 12 pmm of caustic shall be PWHT and can suffer from caustic embritleman, SS can suffer from CSCC.

luis

 

[EdStainless]

In SS this gets a bit more complicated, Temp and minor impurities play a huge role. With SS 15% and 90C I am not too concerned. The CS will be the first limiting issue.

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P.E. Metallurgy, consulting work welcomed

 

short-term warm 15%w caustic case with risk of overheating up to 90°C

I don't have my handy concentration vs. temperature map available, but those conditions seem problematic for 300 series SS.

MTI


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

With SS less than 100C and under 25% should be reasonably safe.

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P.E. Metallurgy, consulting work welcomed

 

[oal223]

Referring to NACE SP040315, At 100 C and lower you are safe. However, it also mention that 30 C margin below the delayed SCC shall be applied to avoid localized caustic concentration and delayed cracking. I think if it only for few hours, than you're fine.

 

[moltenmetal]

Remember that caustic these days is mostly made in membrane electrolysis cells, not by the old mercury-sodium amalgam methos, and they let a little chloride through. Though Cl- SCC is a more severe risk under acid conditions which can initiate pitting (where Cl- SCC cracks apparently inevitably start), 15,000 ppm NaOH could easily contain 150 ppm Cl- even if the water itself contained none to start with.