Passing or leaking valve in H2SO4 service

[Tj01]

Hi Guys,

I have an issue with an H2SO4 manual isolation valve (block) upstream of an automated valve. The Automated valve controls H2So4 supply to the H2So4 scrubber vessel.

Trouble is that this manual valve is not operated regularly and during the maintenance of the automated valve, it does not shut off completely and leaking gaseous H2So4 and Cl2 fumes.

The valve data is:

BALL, VALVE; 8" NB (200MM) JAMESBURY FULL BORE: C/W LOCKING DEVICE: ASME CL150RF, A216 WCB CARBON STEEL BODY & CAP; MONEL BALL.

The seat is PTFE or PFA. See the catalogue attached.

The manual valve does not have any other isolation valve upstream. Hence, to change that out, we have to take the train out.

So far, only option, I have is to replace or refurb the valve proactively but that is in a way difficult as there is always a very tight schedule for labour resources during the shut.

So, I am searching for options to find better material, particularly for seating.

Thanks for the help in advance.

Cheers,

Tj

 

[hacksaw]

Mixing sulfuric and chlorine in carbon steel piping, hmmm.
You need more than a forum discussion, good luck.

 

[LittleInch]

There are many valve sin that attachment. Please tell us which series or page number to look at.

Unless there is space to hot tap two connections on between your manual valve and your automatic valve to insert an inflatable bag and a vent, it looks like you're stuffed as there is no port for injecting "sealant" or a vent inside the ball.

What actually are your seals as the attachment isn't very clear.

Putting an not normally operated manual valve upstream is about as good as you can reasonably do to allow removal of the d/s valve under pressure.

What differential pressure are we talking here? Sometimes there isn't enough sealing force on the seals and vapour can leak past easier than if it was actually under higher pressure. Sometimes. It can sound counterintuitive to do this but sometimes a higher DP gives you lower leakage. Also "exercise" the valve a few times to see if it gets better or worse.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

What is the acid concentration? If you are using steel and CI then this must be VERY high concentration?
You will need to pull the entire train out of service and replace this valve.
No option there.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

As always, LittleInch offers good advice .... do you have enough differential pressure for the existing valve to seal ?

Does the valve leak when the acid reservoir is at low levels, but not so much when the reservior is full ?

You should be in contact with the technical resources of NELES Jamesbury with this sealing pressure question...

For many decades, XOMOX and DURCO valves have been available specifically designed for strong sulfuric acid service ..... My vote is for XOMOX Tufline 061 .... The 8"NPS valve size is the largest available specifically for this service

(The replacement valve will not be cheap...)

http://www.sulphuric-acid.com/techmanual/Strong Acid/sa_valves.htm

Some Questions:

Please supply an abbreviated PID showing all components and materials. What pressure does the valve operate under ?

How long has the system been in service ? What kind of periodic inspection are you performing ?

What is the material and condition of the adjoining piping system ? Has the piping been inspected for the dreaded "Hydrogen Grooving" specific to sulfuric acid (at the 12 o'clock position of the piping)

(There are piping materials available for Concentrated Sulfuric Acid service)

Good information here:

http://www.sulphuric-acid.com/techmanual/strong acid/sa_piping.htm

Tell us more details about the adjoining system .... Can you provide pictures ?






MJCronin
Sr. Process Engineer

 

[bcd]

The catalog shows 2 different NPS 8 constructions. One floating and one trunnion. Which do you have? I am guessing that in your description, you have the letters "NB". Should the be "NT" meaning non-trunnion? So it is floating ball valve? If so, the upstream pressures applied across the valve make a big difference in sealing.

To change seat material, you have to pull the valve from the line. And you don't know if it is a seat material issue. I recommend focusing on the valve history and other possible issues first. The suggestion to cycle the valve a few times to possible clear any debris is always the best place to start.

 

[LittleInch]

NB means nominal bore or NPS.

You don't get floating ball more than 4".

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bcd]

You can get larger than NPS 4 non-trunnion.

Catalog, page 3 shows pressure-temperature tables for both NPS 6 and NPS 8 Non-trunnion.

 

[LittleInch]

OK, Noted - It isn't common though as the forces on the seals go through the roof.

Seems a bit odd.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hacksaw]

TJ01
"I have an issue with an H2SO4 manual isolation valve (block) upstream of an automated valve. The Automated valve controls H2So4 supply to the H2So4 scrubber vessel.

Trouble is that this manual valve is not operated regularly and during the maintenance of the automated valve, it does not shut off completely and leaking gaseous H2So4 and Cl2 fumes."

So you have liquid feed to a scrubber, but it is releasing gases...

Clearly this is a recycle stream of some sort.

What is the MOC of your piping?

 

[hacksaw]

As a follow up, is this a negative pressure scrubber?