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Strength-Weld Tubes To Tubesheet

heat exchanger exchange design

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#1 juche

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Posted 17 June 2015 - 02:03 PM

Hi,

I have been going through one of the Shell and Tube Exchange Data sheet and at the end one note was mentioned saying "Strength-weld tubes to tubesheet". 

 

As i understand this note is to prevent the Leakage from Shell side to Tube or Tube to Shell Side. But how we decide that we need to specify Strength-weld tubes to tubesheet or we can simply tight fit the tube into tube sheet.

 

Exchanger TEMA type is CEU.

 

Exchanger is having a mix of Hydrocarbon & Hydrogen on both Tube and Shell Side. 

 

As i understand we never want any material to leak from tube to shell or from shell to tube side in a tubular heat exchanger.

 

 



#2 fallah

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Posted 17 June 2015 - 03:03 PM

 

But how we decide that we need to specify Strength-weld tubes to tubesheet or we can simply tight fit the tube into tube sheet.

 

juche,

 

I think the service might be "Lethal" or "Toxic" needs to be seal welded...
 



#3 juche

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Posted 23 June 2015 - 11:23 PM

May be you are correct fallah, it is true for many exchanges where i am having H2S or Benzene but few exchanges having Hydrogen and cooling water are also specified with Strength Weld requirement, May be Hydrogen in Cooling tower can be a big safety issue....   



#4 Art Montemayor

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Posted 24 June 2015 - 08:20 AM

I have always seal-welded all heat exchanger tubes involving hydrogen gas - on either the shell or tube side.

 

The reasons for this are:

  • Hydrogen is expensive - especially in the pure state;
  • Hydrogen is one of the smallest molecules (I think Helium is smaller) and it will leak and permeate through the smallest opening - even through steel itself;
  • Hydrogen is a flammable gas.  The Hindenburg Zeppelin proved this.  It will burn with a very slight ignition point - I have seen it ignited solely by the friction generated through a leak in a gasketed flange; it is a hazard in the daytime because it has a colorless flame.  It can only be seen at night.
  • Any hydrogen accumulated in a cooling water system is potential explosion waiting to happen.  The cooling water system should be always vented in a liberal design.


#5 Pilesar

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Posted 24 June 2015 - 10:54 AM

Strength welding the tubes to tubesheets is commonly specified for fixed tubesheet exchangers because of mechanical considerations. When the shell and tubes are assembled, they are at the same temperature. In operation, the shell and tubes will have different temperatures. If the shell is hotter than the tubes, then the tubes will be in tension. When the tubes are hotter than the shell, then the tubes will be in compression. Over time, tubes in tension or compression may start to loosen from the tubesheet. The strength weld is to reinforce the connection of the tubes to the tubesheet. The reason for specifying strength welding is different from the reason for specifying seal welding. I consider a seal weld to perform the role of an impermeable gasket and a strength weld to perform the role of an unbreakable glue.






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