Tube rolling after PWHT or before PWHT 4

[AliBana]

Hi Guys,
Is that possible to expand (Rolling) tube to tubesheet after PWHT? The bundle is in sour services and tubesheet have both tube to tubesheet weld and grove expands area. The hardness of tube expanded area (As measured in a sample) is less than 178 Brinle after rolling.
Is that practical to perform rolling before PWHT? This will not lead to weld cracking during PWHT?

 

[metengr]

Normally, rolling and seal welding of tubes are done with no PWHT. If you need to PWHT, this implies to me that the tube-to-tubesheet joint requires a strength weld, and tube rolling would not be required. Also, PWHT would eliminate all of the benefit associated with tube rolling.

Go back and check to make sure that the tube-to-tubesheet weld joints are only seal welds and not strength (partial penetration) groove welds. If you need to roll the tubes, this would have to be performed after PWHT to derive any benefit from rolling.

 

[gr2vessels]

Is not uncommon to have strength weld and single groove expansion of the tubes in the tubesheet, to prevent the ingrease of corrosive fluid in the space between tubes and the hole, but as metengr said, do the rolling after the PWHT. As hardness concerns, your limit is 248 HV10 so you'll be safe anyway.
gr2vessels

 

[EdStainless]

And one more comment. Make sure that the tubes are lightly rolled (contact only), then welded, PT the welds (this is where you leak test if you are doing it), then strength roll (making sure to stay away from the back edge of the tube sheet), then re-PT a sample of welds.
The order is improtant.
I have seen a lot of cases us rough tubesheet holes instead of actuall grooves. It works just as well.

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[Stanman1]

Although it is common to "lightly roll tubes into tube holes before welding, it has the disadvantage of sealing the space so welding-generated gases can only escape through the weld puddle. This can be a source of porosity and subsurface inclusions. It does not matter whether the weld is a seal weld, partial strength weld or full strength weld as defined in UW-20. What is important is to leave an unexpanded gap of apprximately 50 mm behind the weld root before commencing expanding. If you are very concerned with high residual stress in the transition between the expanded and unexpanded lengths of tubing, consider hydraulic expanding for tubesheets 25 mm thick and thicker. Alternatives for very thick tubesheets with welded and expanded joints are full depth (excluding the 50 mm gap) hydraulic expanding, full depth explosive expanding and full depth hybrid expanding using either hydraulic or explosive to achieve about 3% wall reduction and following with the other uniform pressure method to achieve the final desired percent wall reduction. There is considerable literature on the subject including my recent paper in the Journal of Pressure Technology,

 

[EdStainless]

Stan is right, when I said lightly roll before weld, I ment very lightly and back from the weld. You need to do this to center the tube in the hole so that the weld will be symetrical. But you cannot create a seal.

If you are PWHT then you will roll the tubes afterwards. Tubes that are strength welded must be expanded into the holes. Even though you don't need the strength or sealing you can't risk haveing the tubes loose. I have seen many tubes fatigue at the back face of the tubesheet because they were loose. Not only does this make the first span longer than designed it also allows the tube to impact the edges of the holes.

Stan has been doing this stuff for a long time, read his papers.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rmw]

I gave Stan a star for that. I concur with his advice. If your tubing is so sloppy in the hole that you have to roll to center the tube, you have other problems to solve. If you use the explosive expansion method be sure to place the charge behind the weld so that the weld isn't "banged" by the charge energy.

rmw

 

[Stanman1]

All,

Please correct the gap length behind the weld root in my post. I shoulden't post information when I am half asleep. The gap should be 12.5 mm or slightly more, not 50 mm. Mea Culpa Surprised that no on picked me up short.

Stan