Thin Wall Titanium Tube Plugging? 2

[On3LiFe]

I have thin wall titanium tubes 5/8" OD and 0.028" wall thickness. I am trying to find out what the industry practice plugging thin wall titanium tubes. Has anyone use pop-a-plug with the thin wall titanium tubing yet?

 

[On3LiFe]

The thin wall titanium tubes are installed on a condenser. Main use of the condenser is in sea water.

 

[EdStainless]

Contact Conco and see what they use for Ti plugs.
You need to be careful with any plugs that you don't distort the holes or tubesheet ligaments.

Why are you having to plug tubes? Mechanical damage?

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Plymouth Tube

 

[On3LiFe]

I will contact Conco as well as other vendors such as EST Group.

Why are you having to plug tubes?
This condenser has a square groove design in the tube sheet, when the thin wall titanium tubes were hydraulically expanded, some of the tubes were cracked at the groove(s).

 

[EdStainless]

Sounds like they did three things wrong.
1. Deep grooves with thin wall tubes
2. Poor selection of expansion method
3. lack of mock-up and testing

Holes in Ti tubesheets are rarely grooved since the tubes are usually seal welded in.

You will want to use Ti plugs and weld them in if you expect them to be permanent.

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Plymouth Tube

 

[kingfaruk]

I agree with EdStainless about the grooves. The use of thin wall tubes (here defined as 22 BWG and thinner wall) expanded into square edged grooves (like TEMA type) is simply a recipe for failure. The potential for failure increases with the thinner the wall, especially with titanium material, when expanded across a sharp square edged surface, a shear point, one prone to cracking. Some cracking is therefore to be expected.

Use of either no grooves or shallow multi-v grooves (when higher pull-out strength is required) have been used successfully without cracking using mechanical roller expansion (5 roller). For titanium applications, welding is performed after expanding, so caution must be taken not to contaminate the tubes and tube joint area, and therefore cleanliness is a high priority. High purity isopropyl alcohol, acetone or an environmentally friendly refrigerant have been used as expanding lubricants in lieu of conventional oil or water based lubricants.

As for a corrective action fix, it is suggested that the first step is to have all tube joint areas be NDE inspected for cracks. Identified tubes with cracks can then be removed and replaced with heavier wall tubing (i.e. 20 BWG min. wall). An alternative would be to plug the tubes with titanium plugs at each end sealwelded as EdStainless recommends. Other types of plugs available would be considered a temporary fix. Design specifications for condenser operation may limit the number of tubes that can be plugged without affecting performance.

The use of mockups to qualify the procedure is an excellent and valuable step to be taken prior to production. Unfortunately, mockups contain only a small number of tube joints and these may not identify problems that might occur during actual production with thousands of tube joints. Only through manufacturing and operating experience of a specific material, design, manufacturing and NDE, can one determine the most reliable tube joint for a given application. This advice is based on my more than 30 years of experience designing and manufacturing high quality condensers and heat exchangers.

 

[MJCronin]

on3Life..... Who installed the Ti tubes in your condenser ?

Was this a field refit or were they rolled in a vendpr's shop ?

 

[On3LiFe]

MJCronin. The first question I can not answer and will keep it anonymous. The second question: I do not know whether they were field refit or rolled in a vendor's shop. I a new engineer and trying to learn as much as I could.

Thank You EdStainless and kingfaruk for the information both of you have provided.

 

[kingfaruk]

On3LiFe, you are very welcome. You may want to review a reference entitled "Condenser Application and Maintenance Guide" EPRI Technical Report TR-1003088 August 2001. This 340 page report offers information regarding various plug types that are being used in the condenser and heat exchanger industry. I do recall reading a document that compared various mechanical tube plug designs that studied their leakage rates, so I would use caution when using the mechanical type plugs and recommend a welded type plug for a more permanent solution.

You may want to contact American Power Services (see website

http://www.1aps.com/)

for more information regarding explosive type welded plugs that may fit your application. See the attachment that describes the hollow thimble type plugs that are used on feedwater heaters as a more permanent plug. Other similar type plug designs where welding is employed have been used successfully on condensers.

 

[rmw]

KingFaruk,

The article you posted relates to plugging FWH's which I do advocate and have done on many occasions. However, I never remember seeing an instance of explosively plugging a condenser. Explosive plugging of LP FWH's has resulted in ligament damage and deformation of adjacent tubes, so be cautious, especially if the design has minimum ligament thickness.

Since condensers typically go through much less thermal cycling than a FWH and especially a HP FWH, I'm not sure the case can be made for manual tube plug loosening due to TS differential expansion as can be made with FWH's.

A (manually) welded thimble plug woud suffice as the ultimate in this case IMO. Explosive seems overkill to me especially in the case of Ti. Based on the conditions in most condenser water boxes that I have seen, I don't think I'd want the assignment of arriving at an environment at the tube end clean enough to make a Ti weld. Nasty place to be trying to do welding that requires the cleanliness of Ti welding.

On3LiFe,

IMO Pop-a-Plug plugging - or any plugging for that matter - will plug a tube leak, but if the leak is in the tube to tubesheet joint as you seem to indicate with respect to the cracking at the grooves, it might not seal a Tube to TS leak. You may have to drill the tube out and then plug the TS itself. You don't want to drill completely through the thickness of the TS but leave some of the tube in the TS hole for tube stability or put a stay rod in it if that isn't possible. You don't want a losse tube end banging around in the condenser and damaging adjacent tubes.

rmw

 

[kingfaruk]

rmw, thank you for the caution and advice on explosive plug type. Agree it may be more than needed for this application and that the tubesheet ligament design may limit its use. The information was offered as an alternative to review and consider. A manually welded thimble type plug may be more appropriate for this condenser.

When the process of "hydraulically expanded" tube was mentioned and some tubes cracked at the groove(s), I just assumed the problem concerned a "new" condition at manufacture and that the tubesheets may be thicker than what is typically used on power plant steam condensers. On3LiFe will certainly need to evaluate all the available plugging options for the application. You raise a good point about preparing the tube end for the plug. It may be best to remove (drill/ream) a portion of the tube end so the plug is welded directly to the tubesheet.

On3LiFe will want to talk with tube plug suppliers and service companies to get better educated on what is available for the application and the procedure required for the plugging process. A written procedure with mockup qualification and NDE inspection is recommended.

 

[kingfaruk]

On3LiFe,

Re-thinking your particular case and rmw response, I feel rmw is spot on, as this issue being more a tube-to-tubesheet defect than one of tube leakage, therefore, you will want to focus on "tubesheet" hole plugging and not on tube plugging. rmw's procedure to drill out the tube end and the cautions mentioned seem appropriate for your case. A thimble plug would be welded to the tubesheets at both ends of the tube. So you can forget about the tube plug types available. With a qualified procedure, maintaining cleanliness and performing NDE to verify, simply prepare/remove the tube end and weld in a titanium plug directly to the tubesheet as a permanent fix. Thanks again rmw for your valuable advice.

 

[kingfaruk]

On3LiFe,

The attached patent (1979) may offer you some ideas as to the design of the tubesheet plug for your specific application. The hole preparation may vary (from that described in the patent) to allow for a sound weld between the plug and tubesheet. Possibly the plug could be designed to accomodate automatic welding, same as original welding procedure, should there be a number of tube plugs to be welded.

 

[kingfaruk]

On3LiFe,

Following my previous post, attached is another patent (1980) which involves automatic welding of a tubesheet plug that may offer some ideas should you have a number of plugs to be installed and desire automatic welding be used.

Before tubesheet plugging is considered as a "fix", the first corrective action choice should be to remove the thin 22 BWG cracked tube and install a heavier wall tube. This first action assuming there is ample access to remove defective and install new tubes. One must limit the number of tubes that will no longer be used as heat transfer tubes. There may be other options for a "fix" to maintain the tube as a heat transfer tube (i.e sleeving), although these options might be considered as a temporary fix.

 

[On3LiFe]

Cool. Thanks.