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Tube Buckling

Tube Buckling

(OP)
Hello all and thanks in advance here,

I've got a Shell & Tube Heat exchanger with 4 3/4" thick tubesheets. (Stationary and Floating)
It's a Tema type AES exchanger -- 61" I.D. shell and channel with (2544) 3/4" o.d. Tubes on a 1" 45 degr. rotated sq. pitch.

It's all carbon steel, SA-516-70N except for the 410 S.Stl. Baffles. The tubes are welded SA-214 c.steel, Roller expanded only into the thubesheet.
It has a 5/16" corrosion allowance on the tubeside and runs at 308 psi @ 650 Degrees F. on the shellside and 308 psig @ 650 deg. F. on the tubeside.

My problem is the tubes are overstressed and I have no idea what are where to beef this thing up to eliminate the problem.

I apologize in advance for the length post, but all help is appreciate.

JW

RE: Tube Buckling

Thicker tubes, reduced baffle spacing, or alternate tube material... those are likely your only options.

RE: Tube Buckling

To assist those who may be able to help, pls clarify your operating conditions - they seem to be the same for both tubeside and shellside. Are these mechanical design conditions or the operating range in press / temp ? For operating conditions, state the full range in temp and press.

RE: Tube Buckling

(OP)
Clarification on the design conditions, they are the MAWP, not necessarily the operating conditions:

The exchanger service is " DE-ETHANIZER REBOILER"

The MAWP (shellside) is 308 psi @ 650 with a -20 MDMT @ 308 psi.
The MAWP (tubeside) is 190 psi @ 650 with a -20 MDMT @ 190 psi.

RE: Tube Buckling

How do you know that the tubes were over stressed? What kind of distortion are you seeing?
Is the unit clean? Do operating conditions cycle a lot?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Tube Buckling

You've got to tell us much more...

Tube buckling could be occuring on the heating medium side if steam condensate has some level on the shellside for example on a horizontal kettle. Give us a process description and process control details else you'll have many of us stabbing in the dark.

RE: Tube Buckling

The most common cause of tube buckling is that the floating head does not float.
Or it does not float enough, if the unit is rapidly heated the tubes may expand enough to buckle before the head moves enough to relieve the stress.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Tube Buckling

How many tube passes does the bundle have? If it's more than 2 passes you might want to consider using a "ribbon" flow arrangement, which will minimize the temperature differences between adjacent tube passes.

Another option would be to switch the baffle arrangement to a "No Tubes In Windows" design since NTIW baffles allow for intermediary support baffles, so you can dramatically reduce the unsupported tube length.

Both of these will help prevent tube buckling.

-Christine.

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