Ultimate Guide to Material Properties
MecaStack has a built in database for stack material properties, which are intended to help the designer. There are some common questions and problems that we see when it comes to the use of the stack material properties.
Material Properties are NOT Automatically Updated:
The first step when adding a material to your MecaStack model is to go to the Geometry > Materials selection. In the Materials menu select the “Look Up” option. When a material is selected, a change in the temperature value cells will result in a change for the stack material properties.
Once OK is clicked on the lookup, a SNAPSHOT of these stack material properties are moved to the material form. These are a snapshot, meaning that the values are just the values at the selection of the material and they are no longer linked to the database. If you change the temperature or material on this screen, the properties will NOT be updated. You must go back into the “Look Up” form in order to update the properties.
Why aren’t the properties automatically updated? There are a couple of reasons. Our database doesn’t include every possible material. Sometimes you use a material that is similar to the material you need, and so you use them and then modify the material description. Another reason might be that you don’t want to use the properties exactly as they are imported from the database and this gives you the ability to override those values.
What is the Origin for the Stack Material Properties Data:
Most of the properties came from ASME Sec. II; however, there are also many materials which are not provided in ASME Sec. II, so we have collected from a variety of sources. We now have an interface for the database of the stack material properties that you can open to find the source of the data, as well as the raw data being used in the database.
How does MecaStack handle Cold Temperatures?
If a cold temperature is entered into the “Material Lookup” screen, this is considered in the thermal contraction of the stack. The contraction is mainly a concern on guy wire supported stacks. The other concern with cold temperatures is the materials ability to resist brittle fracture. Currently, MecaStack is not doing any checks with regard to the brittle fracture resistance of the material. This is not really addressed well in the stack codes. The brittle fracture is addressed by the ASME Sec. VIII boiler and pressure vessel code, and so when brittle fracture is a concern this is the code we recommend following. It does not contain data for all materials that are used on stacks, and there is not one clear resource to address this for stacks.
Can you please add Unobtainium to the Database?
We frequently get requests to add a specific material to our database. When data is available, we can do that; however, all too often we do not have sufficient data. We not only need the properties at ambient temperatures (which are often easily found), we also need the reduced properties at elevated temperatures. This can be very difficult, if not impossible to find. The best option in these cases is to find a “comparable” material, and then select that material and change the material specification. It’s not ideal, but it’s often the best option.