Origin of "safe -end" 3

[handlespressure]

In the nuclear pressure vessel world a "safe-end" is a fitting used to transition from a post weld heat treated vessel nozzle. The fitting is installed by the vessel manufacturer and is of a material and thickness compatible with the piping to be attached. Often the attached fitting is a differnt material and the attachment weld is bi-metallic. That is "my" definition based on observation. I have never seen "safe-end" formally defined and I have no idea of the derivation of the term or a braoder use. It could be as simple as a "safe-end" is safe to weld to.

Is anyone aware of 1) a formal definition? Can you 2) add to my definition or 3) give insight into the name derivation? Thanks

 

[unclesyd]

Not familiar with "safe end/ing" in the nuclear industry but is quite common in the heat exchanger field.

Safe ending is primarily used for vertical exchangers where there is a problem with corrosion, cracking. MIC, etc.
We use it on numerous Austenitic SS Hx's to mitigate SCC if the tubesheet vents should fail. We have also safe ended Hastelloy C tubes to prevent corrosion of the tubes in the tubesheet.

 

[metengr]

Just to add to unclesyd's, safe-ending is a practice used to provide transition piece(s) that will be subjected to the same thermal treatment as the item they will be attached to during fabrication. This practice avoids the need for having the entire item and connecting welds exposed to re-heat treatment.

 

[deanc]

There is one older yet. The NBIC calls it "re-end" now but the Steam Locomotive folks called it safe ending.

The FRC made them strip all the tubes out of the boiler on a regular basis for internal inspection.

No sense throwing away an etirely good tube(flue)so they cut off a foot or so and welded on a new end to roll into the tubesheet (fluesheet).

 

[metengr]

deanc;
Thanks for the "older" definition.

PS;the NBIC will be providing a much better description of re-ending, and much better illustration in the 2007 Edition of Part 3 R&A.

 

[unclesyd]

deanc,
We do the exact same same on some steam calandria that use 1 1/8" SS 11ga tubes. We know that the tube will fail in approximately 3+ yrs so they are routinely taken out of service a new end is welded on and the tubes are reused. This gets to be a problem after a couple of rework cycles as the shell had an expansion joint that limits where you can cut the shell.

Anecdotal:
This is where I got my first attaboy when I developed a process and equipment, prior to orbital welding machines, to do an autogenous weld on these tubes.

 

[deanc]

The common practice was to use 2 guys,insert one end of the new "end" in the tubehole and tack weld the old tube to it.

Then while one person turned the tube, the other welded the joint. Most of the time it was a oxy/fuel and you shoved the tube thru the tubehole while it was still hot.

No NDE,No Quals.,No Stamps just a hydro in the end. Times were a bit different and....well, only a few of them blew up.

metengr: Would this be allowed on "old material"? The only place this would make any sense to me would be the 5 or 6" superheater tubes(flues). Do you know if the old FRA laws still apply for interstate use of steam locos?

unclesyd: You ever use inserts?

 

[unclesyd]

Have I every used tube sleeves?
Oh yes they turned an aw-shucks into an attaboy all in one swoop. I have mentioned this before we had two very large vertical condensers that were suffering from SCC and MIC in the worst way. We conducted a very comprehensive tube testing program that indicated Hastelloy C was the ideal choice both from the process and waterside problems. Two new bundles were ordered at a cost of $500,000 ea and upon arrival of the first was quickly installed. We experienced evidence of leaking after two weeks. The leaking became catastrophic very quickly. Upon examination it was revealed that the Hastelloy C were completely dissolving in top tubesheet, temperature. The tubes were pristine at the interface. The other Hastelloy C bundle was on site but based on the current condition of the installed bundle it was a no brainer not to install it. A SS/Inconel bundle was in our shop being rewarded. As this Hx controlled 1/2 our production it had to go online. Out of blind faith I call a sleeve supplier about sleeves. All he had on hand was AL6XN in our size and number. I told him to ship them and a technician. Through the efforts of a very scared technician, the top of the bundle was about 100' up, and our shop personnel we inserted and rolled sleeves in all tubes. We only had to plug a dozen or so. The bundle is still in service after about 15 yrs. The second bundle was sleeved prior to being installed.

We have used Copper Sleeves to protect Hastelloy C tubes in another process.

When we had "Ice House" NH3 condensers we always use a plastic tube sleeve with a vent arrangement built in.

 

[MJCronin]

This thread has some informaton:

http://www.eng-tips.com/viewthread.cfm?qid=73924&page=46

 

[unclesyd]

Just got an update on the Al6XN inserts used in the C276 tube bundle posted on 06/07/07 .

One of the Heat exchangers has been replaced using Inconel 825 tubes and another is on oreder. This new exchanger has been in service for 2 years and is in pristine condition on both the water and process side.

The reason for replacing the sleeved C276 bundle was that it stated to have a few too many leaking tubes. Examination of the tubes after the Hx was removed from service revealed that the leaks were from fatigue failures of the AL6XN sleeve material. This problem stems from the initial installation where I wasn't able to use the proper sleeves. I had to use what was on hand with the realization that remedial measures would have to be taken in the near future. As the initial failure of the C276 tubes was at the backside of the top tube sheet it was realized that that the sleeves should be longer and a heavier gauge than the ones installed to accommodate any tubes that were completely free of the top tubesheet.

The initial sleeve installation worked so well that the reworking of the Heat exchangers was never accomplished.