Diference between tube and shell in asme VIII Div.1

[xgiorg]

Hello!

I'm making the design with ASME VIII Div.1 of a heat exchanger (steam service) and I have some misunderstanding points.

Applying UG-31 it is necesary to use UG-27 (for shells) to calculate the thickness of a tube or pipe.

Diference between tube and shell?

But when I apply UG-27, I have to use UG-16. It talks about a minimum thickness of 1/16 in (UG-16b). But also it is specified in UG-16(b)(3) 1/4 in. and in UG-16(b)(4) 3/32 in. for steam service.

Wich would be the minimum thickness?

This heat exchanger is made with tubes that are welded to a collector (is a bigger tube than the others). I should apply UG-45?

Thanks

 

[SnTMan]

xgiorg, unfortunately, there is not alway consistant terminology used for shells, tubes, pipes, etc. between the Code language and industry terms. Some times product forms are confused with functions.

The tube side of a heat exchanger may be made of plate, tube, pipe, etc., as can the shell side. The tube side collectively contains the "tube side" fluid. The shell side contains the fluid external to the tube side.

For the tubes, you must calculate per UG-31, that is for both internal (UG-27) and external pressure (UG-28).

UG-16 provides an exemption for the tubes of a shell & tube exchanger, plus some other constructions.

Not sure about your details of construction, but it sounds like an integral channel tubeside, or maybe a header type design. Normally UG-45 would not be applied to the main cylinder itself, whch would be governed by UG-16.

Ug-45 is normally applied to connections to the main cylinder.

If possible, get a TEMA book, any edition, for help with terminology and details of construction.

Hope you fine this useful.

Regards,

Mike

 

[xgiorg]

This heat exchanger (economiser) have 2 headers (in/out) with their caps. 100 fintubes (for example 1") connect the headers to make the heat exchange. I'm interested in the min thickness for these fintubes. UG 45 talks about the nozzle neck thickness, that I supose is mandatory in this case for the tubes connecting headers. Then calculating, the minimum thickness for a tube is determined by the UG-16(b).
All in all the minimum thickness for all the diameters of the tubes I would connect to a header (another tube for example of 4") is 1/16 + CA. But for air-water-steam service I have to apply 3/32". Is it correct?

I really don't understand why a fintube that need a thikness of 0,005" + CA in the calculation should use a minimum thickness of 3/32"+CA.

Why does exist pipes of 3/4" with sch 10 (thickness 0.083")?

 

[SnTMan]

xgiorg, Tube thickness is calulated per UG-31, as stated earlier. I see no reason to apply UG-45 to the tubes.

I think the tubes can be exempted from UG-16, however this depends on other details of the design.

Regarding your question about 3/4" pipe, all kinds of things exist. This does not mean a particular thing is suited for a particular purpose.

I would suggest you get some help from an experienced designer.

Regards,

Mike

 

[xgiorg]

Why could be exempted from UG-16? I need some orientation.

 

[stanrick]

See UG-16(b)(2).

What I wonder, though, is when calculating thickness for internal pressure (per UG-27), what value of E do you use for seamless copper (like SB75 C12200 H80).

UW-12 says use E=0.85 for seamless shells, head, etc. But does a copper tube fall under UW?

 

[xgiorg]

Hello everybody

Stanrick, sorry, I don't know, maybe you should create your own thread to ask it.

Continuing with UG-16 I really have a problem of interpretation in this phrase:
UG-16 (b) (2): "This exemption applies whether or not the outer pipe or shell is constructed to code rules."
This means that is mandatory to construct the outer pipe or shell under the code rules or.... independant on applying the code rules to the outer pipe or shell, the exemption applies?

Thanks

 

[eliebl]

In the case of UG-16 (b)(2), you can also apply this exemption to the small types of refrigeration heat exchangers where the shell side is deemed non-code because it is simply carrying water.

My 2 cents.

 

[SnTMan]

xgiorg, UG-16)(b)(2) is interpreted as it reads, that is, the outer containment does not need to be constructed to Code rules.

Stanrick, in my experience E always equals 1 for seamless tubes, assuming you are not fasteneing a head to them, i.e., they are just tubes.

Regards,

Mike

 

[GenB]

a tube do not apply CA but the minimum required
an example tubes of 2 in T .095 may have a min 0.095"
less allowance - 0.055 for pressure calculation,
forget the thickness. you run thickness to satisfy the Code.
if T is yes very thin on calcs+ allowance thats great as long as you do not get below that#.
'hope it helps.