Ikrananka :
Prior to spending a lot of time and money, it might be advisable to instrument the heat exchanger with a vibration analyzer and look at the existing spectrum compared to the number of passes, tube length, pump rotational frequency, and flow rates. It might be quite revealing information. Especially if the unsupported tube length is a harmonic of the pump radian frequency on either the shell side or the tube side. Changing the pump speed and impeller diameter on one or the other flows might just be helpful.
Occasionally, installation of an expansion tank ( or device ) will provide the fluidic dampening necessary to avoid pump induced vibrations on the tube side. Flow induced vibrations from the shell side are another matter.
One very good source of information is TEMA
( Tubular Exchanger Manufacturer's Association ).
mailto:tema@tema.org
TEMA, Inc.
25 North Broadway Tarrytown, NY 10591, USA
TEL

914) 332-0040 FAX

914) 332-1541
As to companies...
There are a good many heat exchanger experts available.
One is Framatome. There are others, to be sure. Framatome has long experience in very large industrial settings with high value or high risk environments. This is not a recommendation, just a recognition that their knowledge base appears to include your area of interest. ( I have no affiliation with this firm )
Framatome Technologies
P.O. Box 10935
Lynchburg, VA 24502-0935
Phone: 804-832-3310
Fax: 804-832-0602
hechg@framatech.com
Best of luck with your situation.
Galgo