Opinion on expansion joint 1

[vesselguy]

The last time I did detailed mechanical design of shell and tube heat exchangers was 12 years ago. I recall I have used bellow type and F&F type expansion joints on shells for Oil & Gas and chemical services. I have even done it to Shell specs. I know it is not prefered but it is not a problem either.

On this current project I'm on, our company standard allows EJ, but our Maintenance chief do not want any exchanger with EJ. I tried to explain to him that the EJ on this BFW Cooler will only flex during temperature cycle during start up and shut down and there should no issue with them failing. But he still insist on no EJ saying the EJ he's worked with on piping have been a maintenance nightmare and so on and so on. I said the EJ he's been concern about are the piping bellows and gimbal joints. It's different for heat exchangers and it is OK to use EJ on heat exchangers designed per ASME Sect VIII, Appendix 5 and 26.

Am I missing some knowledge on operating issues relating the EJ, or is this Maintenance guy way too conservative and mixing up his facts?

I would really appreciate some opinion from experienced exchanger designer and operating people in this forum on my question.

Thanks.


in the last 17 years. Most of the time, I have been designing vessels and packaged equipment.

 

[rzrbk]

I agree with your maintenance guy that expansion joints should be avoided if at all possible, as it causes many headaches down the road. (more prone to leaks, requires special handling during maintenance, makes metallurgy much more critical, etc)

Having said that, there are some special instances where one will be required, such as an exchanger with only one pass on the tube side. Without knowing any more about your exchanger, I don't see why the water cooler could not be a u-tube or floating head type.

 

[vesselguy]

rzrbk,

I keep getting this generalized comment about difficulty duirng maintenance of EJ. What is there to maintain on flange and flute EJ, can you tell me to justify the argument for maintenance? I just want to know.

As for why not u-tube or floating head; for the same duty a U-tube would be larger diameter (approx 1.25 to 1.4 times larger bundle), S or T type are the most costly option and should be used only in challenging fluid service.

 

[rzrbk]

As you state above, I agree most of the concern probably comes from experience with thin wall piping type bellows type expansion joints. Experience with the same is what drove my comments above.

I now have a better handle on what you are talking about and suspect that much of his concern can be alleviated by showing that this is will be a full thickness bulge in the shell (of shell material) instead of a flexible joint. In this case, a picture or a cross sectional drawing will probably save a lot of discussion/arguing.

When you call it an expansion joint your maintenance guy may still be picturing a thin wall, high alloy, arrangement; easily susceptible to physical and chemical damage, as well as requiring specialist welding to repair, despite any explanation to the contrary.

 

[SnTMan]

If you don't really need an expansion joint, F&F works just fine I would stay away from a bellows if at all possible, they can be easily damaged by Bubba's rodeo belt buckle (no offense intended to Bubba), and I had one blow up during a shop hydro one time.

Sometimes though, you gotta have 'em.

Regards,

Mike

 

[rmw]

The maintenance dude is mixing his facts. He is not totally right, but then again he is not all wrong. If your Hx needs an EJ, then it just needs it. If you can design without it, it would be better to do so.

The EJ's he is most familiar with are typically severely abused. Most people use them to keep from having to do a good job of piping design so that there are no stresses or misalignment. Instead of designing piping or ductwork correctly, they just throw in an EJ to cover all the sins. Again, some pieces of equipment have to have EJ's, but that should still be no excuse for poor piping design.

rmw

 

[adrianviorel]

You're quite right, rmw. However, there are still several considerations to be made. Expansion joints are to be used in the situations when, from the very beginning, process designer tells us some dilatations (axial, angular, combined) are to be compensated. In such particular cases, pressures, temperatures, forces to be compensated, etc., can be satisfactorily estimated, and consequently the joints can be designed accordingly. That means, in conditions they are properly mounted, manipulated, etc., the supplier is guaranteeing them for a certain number of compressions/expansions, usually thousands.
On the other hand, EJs ARE NOT designed foolproof, and they will never manage to resist hammers or hammerheads.
Anyhow, EJs can be supplied themselves with hydrotest done, this being able to cool down plant maintenance engineer's fear.