Cor-Ten A properties at 850 F ?

[davefitz]

I would like to use USS Cor-Ten A to form a high temperaure exhaust flue , to convey gas turbine exhaust ( 830 F normal, 850 F max) to a wallboard drying plant. I would prefer to use it as a pressure boundary, and not just a liner . I cannot afford stainless steel for a 750 ft long x 13 ft dia flue.

Can anyone advise if the following properties are published at 850 F?
yield, UTS, creep life, rate of graphitizatiion.

 

[metengr]

In your application of Cor-Ten A plate, it may be difficult to obtain actual elevated temperature mechanical property data because Cor-Ten plate material was designed for application as weathering structural steel at ambient temperature.

I do have a USS Corp handbook at home that lists the various plate steels and it may have elevated temperature property data (UTS, YS and creep data) for Cor-Ten steel. I will check later this evening.

The best approach may be to assume SA-36 steel properties for your first cut, since the Cor-Ten is a copper-bearing, carbon steel plate. It will be somewhat conservative assuming SA-36 material properties, however, I would expect similar behavior of the Cor-Ten plate as SA-36 carbon steel plate at elevated temperature.

Having said this, the yield and tensile properties for SA-36 show a drop beginning at 700 deg F. Above 700 deg F service temperature, the properties of SA-36 are time dependent (creep controlled). Using information from the ASME B&PV Code, SA-36 bar is permitted for use up to 900 deg F for Section VIII, Div 1 applications. The allowable stress value in Section II at 850 deg F is 8.7 Ksi for SA-36 bar material. One of my plate steel reference books shows ASTM A-36 plate to have a yield strength at 30 Ksi, and UTS of 60 Ksi at 850 deg F.

Regarding graphitization, this is something that cannot be easily answered because exposure to both service stress and service temperatures (at or above 800 deg F) play significant roles in determining whether graphitization damage and/or spheroidization damage occurs (these are competing damage mechanisms). I will offer this advice, the risk of graphitization at 850 deg F can be decreased by minimizing service stress (use increased wall thickness).

I would suggest you look at an ASME SA 387 Grade 11 plate (1.25% Cr-1/2%Mo low alloy steel plate) for this application. It could be cheaper than bulking up with Cor-Ten to account for the lower allowable stress value. The allowable stress value at 850 deg F is 16.4 Ksi for SA 387 Grade 11 plate, and there is no risk of graphitization.

 

[davefitz]

Meteng;
Thanks for the quick reply.

The Sa387 grade 11 plate was initially a first choice, but Section II has a note that dissallows seam welded pipe like vessels for sect VIII with that alloy ( must be memories of Mohave) . Also, grade 11 requires PWHT and stress relief, which may be difficult for 12.5 ft dia section 60 ft long. For those reasons I was looking to determine if I could qualify CorTen for this service.

Similarly, all CS sheet found in sect II suitable to 900 F will dissallow seam welded pipe like vessels. Although the vessel officially will not require a code stamp ( as far as I know, Pd < 15 psig), I mean to follow sect VIII rules regardless due to the safety implications.

I have read that CorTen has been successfully used in aeroderivative gas turbine exhaust applications overseas, and if the alloying elements will prevent graphitization at 850 F, I would prefer to use that mat'l and reinforce the seam weld with either a butt plate or overlap style joint ( less than 1% out of roundness). Perhaps that would be adequate for the other CS's mentioned, but the Code notes are a sticking point.

Otherwise, without such qualifying data, the Corten will only be used as a liner and the presssure boundary will be a CS outer shell, the annular space insulted with calsil.

 

[metengr]

davefitz;
I could not find any elevated temperature data for this material. The alloying element in Cor-Ten is essentially copper (0.2-0.4%), which provides for increased corrosion resistance - no real effect on oxidation resistance at elevated temperature. Copper has no real effect on mechanical properties until you exceed about 1%. The chromium is what reduces susceptibility to graphitization damage in carbon steel. Your proposed solution of using Cor-Ten as a liner will creep over time and deform because of exposure to 850 deg F.

I still like your idea of using a liner except I would still go with SA 387 plate - about 1/4" thick. You will not need to SR or PWHT provided your liner thickness is below 1/2". In this case a welded liner of Grade 11 would work very well in terms of creep strength at 850 deg F, and would get you out of having this material as a primary pressure boundary. We have SA 387 Grade 11 ducts in several of our cyclone boilers for gas tempering, and this stuff has lasted for over 35 years!

 

[metengr]

One minor typo correction to the post above ...which provides for increased corrosion resistance and oxidation resistance at elevated temperature...

 

[MikeHalloran]

If you need a flue 750 ft lg. by 13 ft. diameter, it might be cheaper to just move the engine to where you need the heat.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ijzer]

For high temperature there is a special Cor-Ten steel named Cor-Ten High Temp.
The Inland Steel leaflet specifies properties up to 1100 Deg. F