Tubesheet hole pitch changes from grooving

[mcohen]

I work for a company that makes shell and tube exchangers. We are looking into grooving our tubesheet holes for increased strength at our tube-to-tubesheet joint. Based on TEMA, the pitch is defined as 1.25*tube diameter. If circumfrerential grooves are added to the tubesheet holes, does the pitch change? i.e. since the outer most diameter of the tubesheet hole increases, and when expanded, the tube diameter will increase in those grooves, should the pitch be calculated on the groove diameter instead of the original diameter?

 

[saplanti]

I do not remember the TEMA rules right now. However from my power boiler experience the groove height changes from 0.5 mm to 1.2 mm depending on the thickness of the tubesheet, the thickness of the tube etc...

I guess there is no need to play with the pitch at all, and the groove doe not play role in the pitch determination. I suggest you to use the same pitch, there is no need to change it.

In the boiler application we needed to consider the groove in the compansation area calculation only. The tubesheet thickness needs to be suitable to take the tube expansion pressure. The tube is to be expanded into the grooves to seal the connection, and introduce more strength in transfering the tube tension force and bending moment (if available).

Hope it is clear.

Ibrahim Demir

 

[rmw]

Simple answer: no.

rmw

PS: I am not a fan of grooving, but plenty of people are, so who am I to say?

 

[unclesyd]

The world's biggest tubesheet grooving fan, that's the way I was learned.
For years we built and refurbished all our heat exchangers in-house. To the very last one of over 250 HX's the tubesheets are grooved. We used 3 grooves if the tubesheet thickness would allow. The tube pitch never entered into the equation as it was determined by other factors. If the ligament width isn't wide enough you can encounter some rolling problems if you are not careful. In our case this happened a few times when the the tube gauge was changed causing us to increase the pitch ever so slightly due to the fact that the process people didn't like to lose a tube or two.
We also seal welded all tubes after rolling.

 

[rmw]

I hear you unclesyd. Greetings,

rmw

 

[mcohen]

Thanks for your responses. By the way, the material is aluminum. Since it is much softer than steel, wouldn't this influence the pitch? Does anyone know how TEMA derives the pitch equation in the first place?

 

[MrBTU]

The pitch is the center to center dimension of adjacent tubes - it is not dependent on material, or grooving - see TEMA R,C,B 2.5

 

[EdStainless]

I would suggest that you do some testing.
Look at using very shallow grooves very close together instead of the traditional notches (more like scratches).
How they work depends on the relative strength of the tubes and tubesheets. If the tubesheets are softer than the tubes they do not help at all.
If the strengths are similar then many shallow grooves (sometimes made with stiff wire brush) will work fine.
If the tubesheet is stronger then deep notches will work.

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