Short Spool at Spec Break 1

[markovnikov45]

Hi Guys,

I have a spec break with 600# SS (Globe Valve) to 300# LT CS (Ball Valve). Between these 2 valves, a short spool was introduced.

Apparently severe corrosion was identified onto this spool. It is recommended to change short spool material (LT CS A350-LF2).

Having said, should we maintain the same spec with insulation gasket in between or completely remove the short spool?

Thanks,
Mark

 

[racookpe1978]

If you have severe corrosion, why would you want to keep the old material and insulation?

So, assuming you are going to replace the spool with the "other" code material that apparently had not failed, what would you change the insulating (?) or gasket material into?

 

[curtis2004]

Can you give us a bit more information:
1. What is inside pipes?
2. What is temperature?
3. How long doesn it take to see accessive corrosion?
4. How long is SS and LTCS portion of piping?
5. What kind of insulation gaskets were used?
6. Anything else?

Thanks,

Curtis

 

[Gator]

If you completely remove the short spool all the stuff in the piping will probably come out when you start up the line again. Just trying to help...

 

[MickMc]

I think the short spool is required for transition from Class 600 to Class 300. Did you already have insulating gasket set or are you intending to introduce it at material spec break?

Ensure that it is an insulating gasket set with sleeves and washers etc.

 

[markovnikov45]

@curtis2004

1. Blowdown service (gas flaring)
2. -45 F
3. 5 years, give and take
4. 160mm with Flange-to-flange connection, i could't accounted for the whole line length of LTCS and SS, if you asking.
5. Neoprene-faced phenolic
6. Whole line is cold insulated with rockwool

Thanks

 

[markovnikov45]

@MickMC

No, we don't have on the previous design. Currently using Gasket SPW SS/Graphite/SS and Stud A193-b8m.

 

[MickMc]

Your problem may or not be galvanic corrosion due to dissimilar metals and electrolyte present therefore in that case an insulating gasket kit (Pikotek or similar) will help mitigate and even prevent. The insulating kit should be used at interface between dissimilar metals and when your purchasing advise design conditions and service characteristics to manufacturer.

 

[lhwingking]

Hello Markovnikov45,

You have a spool piece in between the two valves.

1. This spool is of SS or LTCS?
2. Can I assume that the line size is at least 4" or more? Because, the required dimensions to bolt a 3" or smaller 300# flange to a 600# flange match as per B16.5 in which case you wouldn't have provided the spool piece in the first place.
3. If this spool gets corroded, won't the pipe of the same MOC upstream / downstream of the valve also get corroded?
If not, can I assume that the fluid was entrapped in between the two valves for a long time and the spool ultimately started losing to pitting corrosion?

Regards,
L. Hariharan.



Never forget what you are. The rest of the world won't. Wear it like an armor and it can never hurt you.

 

[maxdistortion]

It doesn't make sense that only the spool experienced extreme corrosion, I would think its process related less than material. I think you may be trapping fluids.

 

[lhwingking]

@maxdistortion I am thinking the same.

Never forget what you are. The rest of the world won't. Wear it like an armor and it can never hurt you.