cracked bolts on heat exchanger

[231272]

Hello guys,
after instaling new tube bundle of water coller of LPG on crude destilattion unit , bolts on floating head were cracked after few hours of operation (first time 5 hours, second 36 hours).
LPG leaks to the cooling water. Exchanger was hidrotested succesfuly after installation. With old tube bundle we operated ten years without problem.
Do any of you have some esperience with these problem?
Maintance guys think that problem is corrosion and inadequate bolts...process engeneers suppose problem with inproper instalation of tube bundle or inadequate geometry of tube bundle - no space to thermal expansion - floating head does not "floate"
What you think?
Thank you
R.

 

[rmw]

What is the bolting material, the floating head material?

rmw

 

[Jmoore1]

Seeing as how the hydrotest had no issues, there shouldn't be any problem at all at the operating pressure, Bolts may have been over torqued or the floating head did not float, either of these could cause them to fail quite quickly as fixed thermal expansion forces are quite massive.

 

[grampi1]

Normal B7 bolts can crack if the LPG (shellside?) is sour. Is it sour? Did the bolts fail in a brittle fasion, without elongation? Was bolt hardness checked?

 

[JJPellin]

Send the failed bolts to a metallurgical lab. They will tell you if they failed from fatigue, over-stress, environmentally induced cracking (Chloride stress corrosion cracking, hydrogen embrittlement, etc.).

Johnny Pellin