More expansion in SS pipe than CS pipe 1

[Saver2008]

Hi everybody!

I´m trying to calculate the expansion in short system where I have steam at 4 barg at 152°C and ambient temperature is 25°C. The length of my pipe is 5 mts. Well, when I applied to SS pipe, I have the following result: 13.27 mm but then I questioned what if I use carbon steel (cheaper than Stainless steel material) and I have the following result: 9.46 mm....If I compare both results, SS pipe expansion is larger than CS pipe expansion so ...I´d use Carbon Steel pipe but....in my experience Stainless Steel is able for high temperature situations, including this, so....Am I wrong or what am I doing bad?

Thanks!!!!

 

[MiketheEngineer]

I get about a 3.6 mm difference - so your numbers look about right.

3.5 mm is really quite minimal - so what is the problem if the steel pipe can handle the pressures and temps?

 

[Saver2008]

Thanks MiketheEngineer for answering. But taking into account material properties...it is not supposed that SS pipe must have minimum expansion than CS pipe?

 

[MintJulep]

It is supposed that it depends on the exact grades of the material.

In general, austenitic stainless steels have a higher coefficient of thermal expansion than carbon steel. Ferritic stainless would be very close to or less than carbon.

 

[Saver2008]

Thanks MintJulep , but according to your sentence, if SS pipe has a higher coefficient of thermal expansion, it means in some way that SS pipe is more ELASTIC than CS pipe. This will support the result I´m having when calculation is done.

What do you think?

 

[MintJulep]

I think Young's modulus and Coefficient of thermal expansion are different properties.

 

[Saver2008]

Thanks a lot MintJulep,

I´m agreed with you. I tried to say that if we are taking SS pipe comparing to CS pipe, under similar conditions, SS pipe will have more expansion than CS pipe. If we move this to results, length of SS pipe will have a higher value than CS pipe. It means, SS pipe will be larger than CS pipe. What do you think?

 

[MintJulep]

All pipes will get longer when the get hot.

For a given length of pipe if you use stainless the length of expansion will be greater than for carbon steel.

Regardless, if your pipe changes temperature than you need to design for expansion in the piping supports and connections to equipment.

The difference between the two is relatively trivial in terms of design to accommodate for expansion.

If "mts" in your original post is meters than your calculation is off by several orders of magnitude. Over your stated temperature range the thermal expansion of 5 meters of pipe will not be anywhere near as long as 9mm or 13mm. Less than 1 mm. In fact less than 0.1 mm if I've kept track of the zeros correctly.

 

[MintJulep]

Oops, sorry. I did miss a few zeros.

Your expansion lengths seem to be in the ballpark.

 

[rmw]

Saver2008,

I think you are trying to correlate properties that aren't necessarily related to each other. You need to check all the properties of the various metallurgies and make your decision based on what serves your purpose best.

The difference in thermal expansion or the reason for it is probably the least of these.

rmw

 

[flash3780]

Seems like a pretty straightforward problem. My numbers are, of course, not exactly the same as yours since I don't know the exact materials you're dealing with. it looks your calculations look like they're in the ballpark.

delta = L*alpha*dT

1010 Carbon Steel
delta = (5m)(12.2e-6/C)(127C) = 0.007747m = 7.7mm

304 Stainless Steel
delta = (5m)(18.9e-6/C)(127C) = 0.0120015m = 12.0mm

A material's suitability for high temperatures usually isn't based on the CTE, but rather for the strength at temperature. In this temperature range (152C), you can use just about any metal and some plastics if they meet your strength requirements.

Stainless steel is often preferred since it is, in fact, stainless. It will corrode much less than it's carbon steel cousin. Higher temperatures accelerate corrosion. SS pipe/tubing often used in areas where corrosion is unacceptable, such as food processing equipment, laboratory equipment, or in medical equipment.