Hello,

My customer has build a 96 Meter long vertical stainless steel pipework for High Rise Building which is now having leaks on flanges
on the branch piping.Flow Medium is water at room temperature.

They have provided an Anchor at the bottom of pipework and Guide (U-Bolt) at every 3 meters on the remaining vertical portion.
The Pipework is having a DN 100 for the first 50m and remaining portion is DN 80 Pipe. Entire pipe thickness is 1.5 mm.(Trubore pipe)

As per my Caesar-II run check of this pipework, the sustained stress developed is 95 % and there is a downward displacement of 3.8mm observed in the sustained Condition.

My conclusion is that because this is a thin walled pipe, there buckling due to the self-weight of the large pipe. This is causing higher bending stress on the branches due to the downward pipe movement of the pipework.


1. Could you please tell me if this understanding is correct?

2. In Practice, is there a particular height limit for which we can keep building a tall pipe work with just one anchor at the bottom?


Kind regards
Ajmat

Dear Ajmat,
since there is a flange leakage, I wonder... if the flanges have been checked: it could be a bending stress problem due to the high weight of the vertical line, but we need to see the model.

Dear Vanella

Thank you for replying to my post. I have attached the Caesar file.

I am sorry, its a threaded valve (not flanged connection), so the customer are finding leaks in the valves. So since this is a threaded connection, I cannot do a flange leakage check.


regards
Ajmat

Hi Ajmat

I would also consider the static head of the vertical liquid column (96M) which will act at the bottom ie. P= Rho x g x h in addition to the design pressure, which could possibly be the reason the valve is leaking, assuming the valve is at the bottom level.

Hopefully this helps.

Thank you
Best Regards
Ryan Martin

Hi Ryan,

These are threaded valves on the branches which is 80 m above the anchor. I have provided the Caesar file in the above message. I am not able to upload it again due to size constraint.

regards

Ajith Mathews

Hi Ajmat

I had a look at the model and it looks as if there is buckling due to self weight, as there is a downward displacement of the vertical column in sustained, hydro test and operating cases.

Clarification of the branches as-built design is required as I see anchors on the valves with cnodes to the next element....

Need the experts: Dave D, Richard and Mandeep's help on this one.

Thank you
Best Regards
Ryan Martin

Two items about CAESAR II and liquid columns:
1) CAESAR II does not account for any pressure associated with static head, as RyanM points out. If you wish to account for that long column of water in your analysis, you would adjust the entered pressure along the column. But, then, perhaps you are already specifying the bottom pressure throughout the system.
2) Your fluid density adds weight to individual elements. The water in the top of your column is "stuck" to the top element. In fact, the column load of water is resting on whatever pipe surface (e.g., the bottom elbow, 30) or closed valve face you have in that column.

Consuming 95% of your sustained stress allowable limit is within Code but, to me, it is uncomfortably high.

Supporting the base alone (70) may be convenient but a few more supports up the line will reduce the calculated sag and that will reduce the high (sustained) bending stress. I would imagine that spring supports may be required to compensate for differential growth between building and pipe. I am unsure how the building industry treats this.

And what lies beyond your branch ends? You terminate your branches with a Y, GUIDE & RX restraint. Perhaps what continues beyond provides additional bending (about X) which gets you to the leak.

Dave Sir has replied aptly.

My rejoinder is only if you can not afford spring supports and accompanying attachments!

Make U bolts tight gripped with some high friction appropriate pads in between.

Guides need to retain tightness; have spring washers instead of flat washers to retain tight grip without deforming thin SS pipe.

If you provide service to your customer, he will return with gratitude again! In this material world, few of us sincerely do it.

Software gives you options to choose - flex hose in between and multiple supports in vertical run, spring supports or my Jugaad solution!

reg,
sam

Dear Ajit,

I forgot to mention that you need to add some flexibility in branch piping ... asmall flex hose prtion can avoid this leakage.

But, do not forget to support piping at multiple locations.
Reg,
Sam