Thermal coefficient of expansion for S&T exchanger tubes

[vessexst]

Hi guys,

I want to calculate the expansion that tubes of a shell and tube heat exchanger could be subjected to operating at a temperature of 200 Deg C. The tube material is SA 213 TP304L. The material has a nominal composition of 18Cr 18Ni. This categorizes as a group 3 material as per ASME Sec II, Part D, Table TE 1 (austenitic stainless steel).

However, this table lists down three different coefficients of thermal expansion, A (instantaneous coefficient of thermal expansion), B (mean coefficient of thermal expansion) and C(linear thermal expansion).

In order to calculate the expansion that can occur in the tubes, I am using the formula of "alpha*Lo*(delta T).

I am not sure what coefficient value should I be using. Should I go for mean thermal expansion coefficient since its values are quite high as compared to C, the linear coefficient.

Can anybody explain the difference and application of these three types of coefficients?

 

[SnTMan]

vessexst, you'd use the mean, column B. If you'll re-read the General Note you'll see that Column C is expansion in inch / 100 ft. You could use one fifth this value for 20 ft tubes for example for a simplified calculation. Column A is the actual value (instantaneous) at the given temp. I don't really know what its most common use is.

Regards,

Mike

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

 

[waliq]

Use the mean coefficient of thermal expansion for your calculations.

 

[vessexst]

Thanku both of you.

@snTman: Actually I have calculated using both B and C and found almost similar results.
For a tube length of 6.2 meters, if I use coefficient B, for austenitic stainless steels at a temperature of 400 Deg C.

The B value at 400 Deg C is 18.1 * 10^-6. Delta T is 400-20 = 380 Deg C and L0 is 6.2 meters (the initial tube length).
Putting in the formula for linear expansion gives the result of 42.65 mm

Now, at the same temperature, the value of C is 6.9 mm / m. For a tube length of 6.2 m, this gives an overall linear expansion of 6.9*6.2 = 42.78 mm. This is almost the same result as obtained by using B.

However, this value is slightly higher in decimals.

 

[SnTMan]

Actually I have calculated using both B and C and found almost similar results.

No offense, but if this surprises you, you don't understand what you are looking at. Column C data is Column B data calculated on the basis of 100 ft length. In/100 ft at the given temperature. Column B data is in/in/deg F. at the given temperature. (Sorry but I only have US units available). The slight differences are in significant figures / rounding.

Look at the UNITS.

Regards,

Mike



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

 

[waliq]

@snTman: Well, this is what vessexst is saying. Both give similar results. Column C is the actual value of linear expansion (mm/meter). So you can simply calculate the value using C column.

Whereas, the value of column B is the coefficient in (mm/mm Deg C). If you use this value, you need to calculate using the formula vessexst mentioned. So, its basically upto you which column you wish to use depending upon you know what you are doing

 

[SnTMan]

yes

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

 

[r6155]

@ vessexst: some of your numbers are wrong. The expansion is less than 20 mm

Regards

 

[vessexst]

@r6155: Please tell which one??

 

[r6155]

@ vessexst: operating temperature is 200 Deg C or 400 Deg C ?????.

Regards

 

[vessexst]

@r6155: It is 400 Deg C
It was mentioned wrongly in the above information

 

[r6155]

I worked with original post 200 Deg C (18 may 19).

Regards

 

[EdStainless]

And now you see why high temp HX are often built with u-bend tubes.
43mm is a lot of movement to accommodate, and this is a short unit.

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P.E. Metallurgy, Plymouth Tube