Tantalum Plug in Top Head of a Glass Lined Reactor; Function? 1

[plantprowler]

The old glass lined reactor we have says in its specifications that it has a tantalum plug in its top dish. This is not a plug added for repairs later but something that was provided at design.

Now I am ordering a new reactor but the vendor has not provided for a tantalum plug in the top head. I am wondering if I need to provide one and what purpose it serves?

Any thoughts?

Is it to dissipate a dangerous build up of static charges? That was my impression. But the plug is in the top dish; that's not where I suppose one would put it for static dissipation? One may like a liquid contact part?

Is it provided for some other reason?

 

[StoneCold]

Sometimes the glass lining process is not 100% perfect. The reactor probably failed spark testing in that location so the factory added the tantalum patch to solve the problem.
I have asked about adding tantalum diptubes to help with static dissipation as we mix straight Hexane in some of our processes and it can build up enough charge to damage the glass.
The response from the glass lined vessel manufacturer was that it would not help. We did have an old reactor though, that ran a lot of hexane processes, once the number of 1-1/2" tantalum patches reached 19 the reactor stopped arcing through the glass, presumably because the tantalum dispersed the hexane charge. Either that or the rest of the glass was thicker than the 60 thousandths minimum.

Regards
StoneCold

 

[ehbadger]

AS StoneCold alluded to, the Ta patch is more than likely just that, a patch. It is one of the most common, reliable repair techniques for a defect in the glass (if not at "sharp" radius/curvature area). Perhaps there was a defect in the initial manufacturing, and rather than scrap the entire piece and reglass it (adding cost/lead time), the manufacturer likely obtained approval from your company to use the patch. As such it would be on the original drawing and not the result of a subsequent repair.

I've not heard of a patch being used for static dissipation. I believe Pfaudler offers an anti-static glass (ASG) but I've not used it myself. De Dietrich may have an equivalent. It is probably worth reaching out to them and investigating that rather than trying to use what would be a VERY expensive dip tube.

[link ]

https://www.pfaudler.com/en/products/glass-linings

[/url]

 

[plantprowler]

Thanks @ehbadger & @Stonecold:

I investigated more and it does not seem like a damage-repair patch. Reason I say this is that I located the original files & within them there is the corresponding quotation. That says:

"tantalum plug provided on top dish"
​

So it does look like it was provided by design.

 

[shvet]

See ISO 28721-1:2008
"6.1 Repairing with plugs
Defects in the enamel shall be repaired with tantalum plugs and polytetrafluoroethylene (PTFE) gaskets.
..."

 

[plantprowler]

@shvet

Thanks. Indeed plugs are used for lining repairs.

My question is, do they have any other function?

 

[plantprowler]

@Stonecold

Dumb & off-topic question: How did you realize that your reactor finally stopped arcing through the glass at Plug #19?

Could you hear / see it? Or.....?

Just curious.

 

[Latexman]

If the tantalum plug was for static dissipation it would be in the bottom head. It's a repair.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[LittleInch]

It might be a relic from when they turned the head? or spun it when applying the coating?

I got a response one time from a supplier when we questioned what appeared to be a welded plug in the centre of the head and there is a clause in ASME VIII that a certain size hole in the head is allowed due to manufacturing technique and it is not classified as a repair.

http://www.cmforming.com/pdfs/asme-code-type-flanged-dished.pdf

go to second para of second page



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

 

[StoneCold]

PlantProwler.
When you stir pure hexane static builds up to very high voltages. So when it finally discharges it arcs through the glass at a weak point. The arcing will blow a chunk of glass off about the size of a nickel. Sometimes the glass will fall off immediately and sometimes there is a delay of a few minutes or hours. Anyway when the reactor stopped loosing glass that is when we assumed that we had so many plugs that they were effectively grounding the reactor and dissipating the static charge. It is not a policy I would recommend, I actually encourage mixing small percentage (10%)of a very conductive solvent to hexane so that this problem goes away. We use methanol or tetrahydrofuran to help dissipate the charge.


Regards
StoneCold

 

[plantprowler]

@Stonecold

Very interesting. I did not know this.

 

[glsinfo]

I've worked for both GLS firms for many years and have the following comments:
1) Ta plugs are used as repair material for 99% of applications. Occasionally you would have a request for a grounding plug, but typically in the liq. phase as mentioned above. Most likely this plug is related to a "holiday" discovered during final spark test. Depending upon the vessels age, a certain # of plugs were allowed based upon capacity, for brand new vessels. Now adays, it is much rarer to have a new vessel with a plug, due to manufacturing and coating improvements by both firms.

2) Related to the use of plugs for dissipating static electric. PLEASE BE VERY CAREFUL, plugs are not the solution for this issue. Static electric discharge is a point to point occurrence, and while the plug may help dissipate the build up in one area, it does not protect the vessel or resolve the hazard. You must maintain a intert atmosphere and break the fire triangle. Static electricity is a hazardous issue to alloy vessels for this same reason. There are experts in this field that can be consulted on this (I am not, I am raising caution on some discussion comments above).