best sequence for tube rolling on tubesheet

[srijey]

What is the best sequence- preferred order of rolling or strength welding of tubes on a tubesheet layout in a shell and tube heat exchanger? I'm interested in knowing how to determine the order and how it affects the tubesheet warping or is it just based on convenience of fabrication?

 

[gr2vessels]

Strength welding after tube rolling tends to affect the tightness of rolling, due to the thermal expansion of the tube. Also, hot air blow-out at the weld closure.
Suggest welding first, then rolling. Note, when seal weld only, you should roll the tube first.
This topic has been a very disputed in past, check out the previous posts.
Cheers,
gr2vessels

 

[srijey]

I'm challenged in expressing my question graphically!!!!! I wanted to know the sequence (order of rolling or welding of the tubes) of operation of tube to tube joint on a tubesheet layout. Where do you start on the tubesheet, where you end and what is the pattern and why? Do you start from outside to inside of the tubesheet (with finished holes), from inside to outside, from top to bottom, from side to side and so on? If I am still dumb in properly putting forward my question, please help me.

 

[srijey]

I made again an error. These are tube to tubesheet joints and not tube to tube joints. This question pertains to the preferred order of rolling or welding operation in the shop over a tubesheet layout with finished holes.

 

[rmw]

How large of a tubesheet are you talking about? If it is a condenser tubesheet that is say 4 meters by 6 meters, and contains tens of thousands of tubes, the tube rollning matters a lot.

If it is a tubesheet about 1 meter in diameter, not so much.

Gr2vessels has made some good points about when to roll and when to weld. I'd add that you may want to consider a contact roll before welding. This isn't a hard roll, just a roll that barely contacts the wall of the tubesheet hole and centers the tube in the hole. Then after welding do the hard roll.

rmw

 

[srijey]

Let me try to make my English clear: My question is not about tube rolling or welding which one cones first. This is nothing to do with a single tube sheet to tube joint. I'm talking about sequence of operation of joining tubes to tube joints on a large tube sheet. Do you start from periphery to centre or from centre to periphery of the tubesheet or any other pattern? If I understand rmw correct, up to 4m dia, there is no need to follow any order; just perform joining from anywhere on the tubesheet. I believe there is some method which will impart less stress on the adjacent tubes. You join alternate tubes in a pitch and not adjacent ones.

 

[SnTMan]

srijey, there may be some unusual configurations where order is important, but in my experience pretty much all the time, rolling is performed sequentially along rows, top down, bottom up, right to left, left to right, matter of convenience.

What is important is to not miss any tubes.

Regards,

Mike

 

[muld0020]

I agree with the other post, however, I would add that there is a slight preference in expansion. The tubesheet will "grow" as you expand the tubes into the tubesheet and it is cumulative across the holes. You will see this effect much more when the materials are soft copper alloy. Therefore it is recommended to work from the inside out, to prevent accumulation of the residual stress and expand to the correct wall reduction. You should take this into account when you design your tubesheet and tubejoint, some designs it matters most it does not. The designs that matter are typically when you have a pull through floating tubesheet, where you have to meet certain tolerances.

 

[EdStainless]

The other thing is to divide the tubesheet into 'blocks'. Roughly squarish areas that will be rolled one right after the other.
The number of tubes in each will depend on your QA and tooling maintenance procedures. I have seen these drawn on the tubesheet with marking chalk while the tubes are being installed.
Often you see people roll 50-100 tubes (depending on size of unit) between quality checks and expander replacement. While the operator is changing expanders and verifying torque setting the QA guy is taking his check dimensions. Then of course the used expander is cleaned and inspected and put back into rotation.
This process allows you to keep track of smaller groups of tubes at a time and to skip around the tubesheet with less risk of missing tubes.

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Plymouth Tube

 

[srijey]

Thank you for the responses. I've seen in the past that rolled tubes start relaxing when we roll soft adjacent tubes (like brass or CS). That is why I was wondering how come there is no recommended practice available. Inside - Out approach seems to be good to address this issue. In the case of welded tubes, I'm not sure how the rate of heat input will affect the adjacent holes.