Shell and Tube Thimble Plug for leaking tube 1

[iangineer]

Hi all, and happy new year!

I come to you today to ask for any assistance or knowledge on the use of thimble plugs for plugging a leaking tube in an exchanger. I cannot find any information about them online and am not sure where to look in any code books. I have attached a drawing of one and have been tasked with writing a repair plan for its installation. I had recommended welding tapered plugs into the leaking tubes, but these thimbles were ordered instead.

Basically, it will be held with the opening facing the channel side of the tubesheet. It will be flush with the tubesheet and welded into place around the rim.

Do any of you have any experience with thimble plugs and have any suggestions for installation, please?

Thank you

 

[MJCronin]

What a poor design ... What "rocket scientist" in purchasing decided on using these ?

As defacto HX engineer, why are you not specifying the methods and types of repairs to be performed

They must be more expensive than the typical tapered conical plug ...

Are these "thimble plugs" event meant to be used on STHXs ??? ... Are we examining a convoluted mistake made by purchasing ?

Was there any information given by the HX fabricator/vendor about acceptable tube plugging ?

Oh, wait .... You just got hired a few months ago and management/maintenance department has thrown away all paper records ... I remember

More information, please

MJCronin
Sr. Process Engineer

 

[EdStainless]

Are they the same metallurgy as the tubes?
Did someone actually measure the tube ID size before ordering these?
Do you have a qualified weld procedure?
If those are not all yes, then likely these are unusable with any degree of reliability.

How thick are your tubes and tubesheets?
There usually needs to be at least a snug fit.
For thin tubes and tubesheets traditional tapered plugs are a bad idea because of the risk of distortion.
But for general use they are great.
There are both one piece and two-piece tapered plugs.
As well as some very good mechanically expanding plugs (pop-a-plug).

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

 

[SnTMan]

We used someting like that at a previous employer, but most of the details escape me.

As I recall, they were sized as a light drive fit into the tube, then seal welded. Intended to seal tube leaks only, not leaking joints.

iangineer, question: Where did you get the drawing? Might there be more information available from the source?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

The person who made this drawing must take training.

Regards

 

[iangineer]

All,

Thank you for your responses. I was able to get a hold of the vendor since posting on here and received a little more information.

From the vendor sales rep: One vendor engineer responded with, "No, there is no installation instructions, they just weld it in place." When asked if the intent of the hole was to allow for rolling, another vendor engineer responded, "The plugs were designed to be welded, can't tell if they can be rolled. The hole in the plug is to make it lighter and easier to hold in place. The hole is the reason they call it a thimble, because that's what it looks like." (duh) "The other reason for the hole was to allow for some flex to help keep the shrink from cooling after welding from causing the rolled and welded tube from pulling away from the tubesheet."

MJCronin:
They are more expensive. The tubes in this exchanger are 4.5" OD. The response from the vendor's engineering team was, "This is way too big for a Snap-It. The temperature is too high for a GripSafe. Tapered tube plugs are not rated to this pressure. We can make a custom thimble plug to weld in for this application." So that's what they did.

Looking at past inspection photos, it looks like tapered plugs were welded into place, so I'm not sure why they didn't do that again.

EdStainless:
The plugs are the same material (316SS) as the tubes and tubesheet. The vessel was in service at the time and exact ID measurements could not be taken. We do have a qualified weld procedure.
Tubesheet thickness = 4.725" CS with 0.59" 316/316L cladding on tube side
Tubes are 4.5" OD, 0.141" nom thickness.
Shellside design P&T = 300 psig @ 660°F
Tubeside design P&T = 75 psig @ 400°F

SnTMan:
These are for tube leaks. The vendor sent the drawing. I removed detailed information so y'all could have an idea of what the plug looked like.

I did find this thread LINK that mentioned thimble plugs, but it didn't really help a whole lot.

I followed up with the unit installing the plugs and they said three tubes were successfully plugged. They pressure tested, found another tube leak, and plugged it, too. They ordered 16 total of these plugs in case more leaks were found.

Thanks again for your help and responses!

 

[EdStainless]

OK, with 4.5" I understand using these.
The stress argument is a valid one.
At that size I would expect the guys installing them to 'adjust' the size slightly so that they would fit snuggly.
It sure would make welding easier.

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

 

[r6155]

How old is this HE in service?
Did you check the tubes for external pressure?

Regards