Leakages in High pressure Urea grade nozzles, lens gaskets.

[EngTal]

How to handle a situation in which there is a Urea-Carbamate leakage through a High-pressure Urea grade nozzle and lens gasket.
What to do if the tightening margin is finished after hot tightening?
What should we take care of during installation to avoid such leakages after plant startup?

 

[MJCronin]

"What to do if the tightening margin is finished after hot tightening?"

What do you mean, exactly ?... Did you run out of threads or are you at "max-torque" for that stud ..

Based on your photo, it appears that you have too many stud threads "left over" after tightening your flamnge down

MJCronin
Sr. Process Engineer

 

[EngTal]

By no tightening margin I meant, the nut won’t further rotate upon striking the spanner. Also the(hexagonal)edges of the nut are getting damaged.

A picture of the assembly is attached.

 

[Heaviside1925]

OP,
The link below may provide answers your questions.

https://www.europeansealing.com/wp-content/uploads/2018/05/GasketHandbook-03-02-17-1.pdf

If I had to guess from the pictures, one of the mating surfaces is damaged or improper torquing sequence was used.

 

[LittleInch]

What type and rating of flange are we looking at here?

Those studs look to have a very fine thread or is that me?

Also are you trying to force this into place? Tightening will only get you so far off the was a gap before you started bolting up.

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

 

[EdStainless]

Getting uniform load on a gasket requires a very careful tightening procedure.
'As tight as we can' is never part of it.

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

 

[TugboatEng]

Is there a hole drilled in the gasket for a tap? That appears to be the case. Perhaps the hole has weakened the gasket.

 

[EngTal]

Hi LittleInch,
This is a threaded flange on a Urea grade nozzle. Rating is above 2500Lb (special rating for UG). Studs have threads in accordance with ANSI B 1.20.1 NPSM.
No, we are not trying to force this into place. I mean there these spools are properly aligned and have minimal or no stress in them.
Basically, what I am trying to ask is how to act in such situations. What are the methods to contain these leakages. Are there any out of the box solutions to rectify such leakages online?
Should we proceed towards box up of this joint. In our plant's history, such joints were never boxed up upon such leakages. We just apply Low pressure steam to continually flush leaking urea carbamate to prevent crevice corrosion.

Hi EdStainless,

You are right. Uniform load on a gasket is very important and greatly depends upon finish of sealing faces and tightening procedure.

Hi TugboatEng,

No, there is no hole drilled in the gasket. It's a drip ring. This hole beneath the gasket is an integral part of it.

 

[XL83NL]

the nut won’t further rotate upon striking the spanner.

This worries me. I would assume that with such studs, this will either be hydraulically tightened or using bolt tensioners. Then what do you require a spanner for?

What flange tightening procedure are you following? Do you have any at all? Does the procedure by any means align with industry standards like PCC-1? Have you checked PCC-1 (e.g. appendix P) to define a typical approach for troubleshooting leaking flanges?

As per the previous replies, too much details are missing to give (free and solid) advice.


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

 

[LittleInch]

NPSM is not normal flange type bolts which are usually 8UN, or 8 threads per inch. That's not what you have.

What type of gasket do you have?

ASME PCC-1 gives good guidance. Also for better sealing could you use some sort of hydraulic tensioner?

To solve leakage you really need to break the joint, clean the sealing surfaces and use new gaskets and keep it all very clean and the torque it up in steady steps.

Simply secondary sealing it won't work.

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

 

[tigny]

Hello,

we cannot see any lubricant around the studs/nuts on the overall view.

As stated by LittleInch, ASME PCC-1-2022 give guidance on lubrication (check Figure 8.1), which doesn't seem fulfilled. We should see excess of lubricant.

You may have attained you torque, but not have developped much tension, due to friction in threads and under the nuts?

 

[r6155]

NEVER use torque. Use Stud elongation with hydraulic tensioner.
Regards.

 

[r6155]

Lubrication is very important when using torque, for installation and disassembly.
Lubrication (not required) is not a problem for the hydraulic tensioner.

Regards

 

[TugboatEng]

Maybe it's the angle but it sure looks like there is a pipe tapped into your gasket.

 

[EngTal]

Dear TugboatEng,

This is a drip ring. That tapping is an integral part of the gasket. I will attach a picture of it below for your info.

This link contains information about Drip rings and lens gasket.

:

https://www.meccanicapadana.com/intranet/libretti/libretto123-01-1.pdf

 

[LittleInch]

Ah,

So you have two sealing surfaces on that side of the valve?

what exactly is your sealing material? some sort of strange curved seal ring?

Or is this drip ring thing the "gasket"??

I need a decent drawing here and a link to some specs

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

 

[EngTal]

Hi LittleInch,

Yes, this drip ring acting as a gasket here. It has two sealing surfaces like lens gasket. The drawing and specs of it are mentioned in the link attached.

https://www.meccanicapadana.com/intranet/libretti/libretto123-01-1.pdf

 

[TugboatEng]

I'm stuck on that drip tube because it's so unusual to me, but so is a lens gasket. The drip tube appears to be attached to something. Does this put the tube to gasket connection under a moment load? This may distort the gasket and cause leakage. It's only this gasket that cause trouble, no?

 

[A8yssUK]

Hi there,

If you have been attempting to stop the leak by hot torqueing (bolting up while the thing is in service and hot). Then shut down immediately and replace the whole thing you have likely broken the bolts, flange, gasket and/or possibly valve. You should never do this, I get why you tried it as a last resort but if it hasn't worked and now the nuts are damaged and max'd out... you've almost certainly broken something.

Consult the gasket and/or valve manufacturer immediately, so they can also tell you the same thing, because you also shouldn't trust some random guy on the internet...

 

[LittleInch]

What does the flange look like?
I've never seen anything quite like this.

There seems to be a very small contact sealing area so any small surface defect will leak.

Is the seal the correct (soft) hardness?

Also as tug says any small force on that pipe will disturb the seal.

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