MAWP - Maximum Metal Temperature and Failing Refractory

If you plot temperature and pressure on two axes of a graph, Chief, you can draw a line that represents the maximum temperature-pressure envelope for the metal in question. If you're below the line, you're safe. Above the line, you're heading for Bang City, Arizona. Is that what you want?

All it does is relate the yield point of the metal to its temperature. I'm sure someone on here can point to it.

Toodle pip!

Thank you - yes, this is definately close to what I am looking for. Is the pressure/temp a linear relationship, or does it depend on the alloy used?

I have been looking through the API stndrd (#?) on "Fitness for Service", but am not quite finding what I need (i.e., haven't found it yet!); any thoughts?

Please look at ASME Boiler and Boiler and Pressure Vessel Code, Section II - Part D

The same graph in Customary units : MAWP in PSI & Design Temperature in ^oF

Something strange, when I copy from Excel and past here of the second graph at my post #5 to be in Customary units, I found that the preceding graph in SI units at my post #4 has changed to become the same of the other graph in Customary units, instead the time of graph in post #4 (15 min.) had been finished and there is no chance to edit it.

How can this happen?

Thank you for your reply! I so want to see the graph, unfortunately, I am having problems viewing the image. Mozilla is my browser, tried altering options, no luck. I tried viewing with Internet Explorer, altered options, and still no luck. Any ideas?

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Important note. When I opened the CR4 Forum tonight, I noticed that 3 graphs removed and the fourth exchanged by a picture for woman face extracted from a word file just created one hour ago. And I am astonished, how that pic attained to that place of CR4.

I'd like to ask the CR4 administrator, and please try to help me by answering the two questions:

1. Is there a espionage process, where such a person or group spying my PC?

2. What is the cause of disappearing of graphs and then appear just insert a new graph?

2. How do you interpret all what happened especially the exchanging of graph with the woman pic?

Use the following link to down load the graphs: MAWP_versus_Temperature_of_a_Pressure_Vessel

Dear Ifit5 -

Try not to become confused by "design" conditions and "maximum" conditions, which are different. For example, lets say that your "design" conditions are 55 psig (379.1 kPa) and 475 deg F (246 deg C) and your calculated wall thickness is determined to be 0.412" (10.465 mm) for the material of construction you are using. You will build the unit out of 11 mm or 12 mm plate. Allowable stresses will be taken from ASME Sec VIII based on 500 degree F maximum temperature {650 deg F for carbon steel}(unless Division 2 is used). By using 500 deg F and 11 mm plate and back calculating you determine that the pressure could be 62 psig (427.4 kPa). {All numbers are only theoretical, not actual.} Now your design values for Temperature and Pressure are 475 deg F and 55 psig (246 C / 379.1 kPa) and your MAWP is 62 psig (427.4 kPa - based on the actual material used) and your MMT (maximum metal temperature) is 500 deg F based on the allowable stress charts. I have always used the expected maximum "design" temperature as the "maximum allowable working temperature" even though that should be calculated based on the MAWP and allowable stress values and should be closer to the MMT. Note that all pressure and temperature values are to be determined based on the "weakest component" of the vessel, not just on the wall thickness, so all nozzles, covers, flanges, etc. need to be considered in your analysis. I've used the wall only as a simple example.

For any single vessel you can develop a graph for temperature/pressure, as indicated, but this would need to be done for each vessel involved and using the "maximum" values instead of "design" values to be of any practical value.

"...the temperature is exceeding the max metal temp listed on the code stamp. Theoretically, couldn't this affect the MAWP of the vessel?"

Yes, once the material of construction is set, the "maximum" pressure will be dependent on the allowable stress values, which are temperature dependent.

"Try not to become confused by "design" conditions and "maximum" conditions, which are different"

No, the both are the same, where the design condition is the max. expected or most severe condition of coincident pressure and temperature expected in normal operation as defined by the codes. (see ASME VIII-1, Para. UG-21).

You are assuming I meant "maximum design conditions" when I stated "maximum" conditions. This was not my intent and I apologize for any confusion I may have caused. I agree any pressure vessel must be designed for the maximum temperature and pressure expected during operation.

What I meant was that "Design conditions" are dictated by the process involved. "Maximum Allowable Working Pressure/Temperature" (what I referred to as "maximum conditions") are dictated by the Materials of Construction selected and may be the same as the design conditions, but, in general, will exceed the design conditions.

Thanks to everyone who replied – I really appreciate the help! So, as I understand it from the replies, during process design, you have a set of target parameters (temperature and pressure) for normal operations. Using the maximum expected design conditions and materials of construction, wall thickness for the vessel is determined. Since metal plate comes in fixed sizes, the materials used to construct the vessel will be thicker than what is calculated as needed for process design. Using the actual materials of construction for the vessel, also taking into account other components of the vessel (nozzles, flanges, etc.), maximum allowable temperature and pressure for the vessel is determined (per ASME code used for vessel design).

Thus, it sounds as if, for the most part, MAWP for the vessel will exceed expected max design pressure. In your experience, is this also the case for MMT?

Vessel design is dependent on both pressure and temperature. Both values are required to determine the minimum material requirements for the design. However, temperature is only used to determine the allowable stress for the material being considered. As such, it is not a factor in determining the material thickness, weld requirements, nozzle thickness/attachment, etc. for the vessel other than specifying the allowable stress, "S", to use in the calculations.

For determination of the MAWP my experience is that the materials of construction and vessel design are determined from the maximum expected design conditions of temperature and pressure and material selections made. Then the "allowable pressure", equal to or above the design pressure, is back-calculated using the actual material thickness used (as you have summarized). However, with temperature, we have assumed the MMT to be the maximum temperature in the ASME Code Tables (Subsection C) at which the allowable stress does not change for the design pressure specified.

For example, assume SA-516-70 carbon steel material. Allowable stress values do not change up to 650 deg. F. Therefore the MMT would be 650 deg. F for any vessel designed for pressure and temperature below that. However, for a vessel designed from SA-240 material, the allowable stress values change for each 100 degree increment above 100 deg. F. Therefore, the MMT would be the next higher increment that does not affect the allowable stress. In other words, for a vessel designed for 150 deg. F operating/design, the MMT would be 199 deg F because at 200 deg F the allowable stress values change. (Many designers would just use 200 deg. F for convenience.) At least this is how I have always worked it.

In posts #4, #5 and #8, the disappeared curves of MAWP versus Temp. of Pressure Vessel are: