HX tube min thickness

[NovaStark]

Good day all,

Currently I have a heat exchanger which heats incoming air (via straight finned tubes) using steam.

Tubeside on steam, and air on the shellside.

Looking at the design code, it is designed to ASME 8 Div.1 for which the tube is specified as 1 inch and 1/16" thick.

Now for the design of 75 psi and 600F, this thickness should be sufficient for the carbon steel tubes however my knowledge of the code would indicate that for air/steam service the min. thickness of the tube should be 3/32 (0.094) inches.

Strangely now if this is correct, then my exchanger should not have a U stamp as it currently does.

Am I correct in my interpretation of the code wrt to this ?


[Note that the drawings do not indicate TEMA or similar]

 

[pdiculous963]

Read UG-16(b). There are exemptions for heat exchanger tubes to the minimum thickness you outline in your post.

 

[SnTMan]

Strangely now if this is correct, then my exchanger should not have a U stamp as it currently does.

Why would you say that?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[NovaStark]

Read UG-16(b). There are exemptions for heat exchanger tubes to the minimum thickness you outline in your post.

This is what I was reading as follows:

the minimum thickness of shells and heads used in compressed air service, steam service, and water service, made from materials listed in Table UCS-23, shall be 3/32 in. (2.5 mm) exclusive of any corrosion allowance

Which I took to mean that the thickness should be a min of 3/32 inches.

Why would you say that?

I was under the impression that if the thickness isn't the minimum code [the U-1A form also has completely different nominal thickness as well], then it would not be an ASME designed vessel. Unless the U-stamp is different (my knowledge on these things is a bit limited, trying to learn/understand better here).

 

[EdStainless]

It says "heads and shells", nothing about tubes.
For various services and materials there are sometimes minimum wall thickness requirements.
Get to know the Code.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[NovaStark]

It says "heads and shells", nothing about tubes.
For various services and materials there are sometimes minimum wall thickness requirements.
Get to know the Code.

Is it correct to then say that a shell is not the same as tube ? (As I have seen the shells under internal pressure used to calculate "tubes under internal pressure")

 

[pdiculous963]

I would look at UG-16(b)(2). If you have a typical shell and tube HEX, with the tubes internal to the shell, the structural minimum of 1/16 does not apply as they are protected.

this minimum thickness does not apply to the inner pipe of double pipe heat exchangers nor to pipes and tubes that are enclosed and protected from mechanical damage by a shell, casing, or ducting, here such pipes or tubes are NPS 6 (DN 150) and less.

 

[NovaStark]

Thanks, I'll look it up.