differences between charts and graphs
differences between charts and graphs
(OP)
Did anybody noticed the differences between the charts and the graphs of several material groups? (we use the metric ones)
I even think there are some errors in the charts.
We use the charts in our excel calculation sheets, and we came across some deviations.
Does somebody else uses the charts?
And what do you do with the incorrect values?
Is it allowed to correct these values in the charts?
Or do we have to calculate with the (in my opinion) faulty values?
Jeroen.
I even think there are some errors in the charts.
We use the charts in our excel calculation sheets, and we came across some deviations.
Does somebody else uses the charts?
And what do you do with the incorrect values?
Is it allowed to correct these values in the charts?
Or do we have to calculate with the (in my opinion) faulty values?
Jeroen.





RE: differences between charts and graphs
To cut short if you like you can refer your spreadsheet by attaching it, and referencing the codes you are using.
Otherwise, my guess, you will not get the answer you are looking for.
Hope it helps.
RE: differences between charts and graphs
I'm looking through the external pressure charts in ASME.
The charts I have found 'errors' are:
- CS-6
- NFN-12
- NFN-14
- NFN-15
- NFN-16
- NFN-18
The graphs I created in Excel are crossing each other, some worse then others, but it's certainly not very good looking. The values I entered are checked and double checked. You can verify my graphs easily by entering the tables in excel.
I think it would not be that difficult for ASME to create a nice set of matching graphs and tables.
Next to these errors mentionned, there are also some typo's in the tables:
- NFN-9: metric - 705°C - "A=3.0 e-3" should be "3.0 e-2" (this is correct in the customary table)
- NFN-18: metric and customary: B-value corresponding with the lowest A-value and lowest temperature: B should be 20MPa / 2.84psi. I assume this is a typo in the customary table, copied to the metric table. (see graph to verify)
- NFN-18: metric - 260°C - lowest A value misses a '0' (zero).
The biggest issue would be that it isn't allowed to alter these tables when using them. OK, I *might* be correct here, but I can imagine allowing corrections leads to custom adaptations to correct calculations....
RE: differences between charts and graphs
I always used the charts not the tables. However, I would expect they are more or less identical.
Hope this helps.
RE: differences between charts and graphs
RE: differences between charts and graphs
But, they are both logatythmic in my examples, just like in the ASME book, to show similar graphs.
It is true that we need to interpolate logatythmic between points, and that the results will be less rugged.
But, all this does not solve the fact that a point of a higher temperature line jumps over a lower temperature line.
(example: NFN12 - 95° line, NFN16 - 425° line)
Or, the other error on NFN18: the 20° line should be colinear to the 95° line according to the graphs.
And for difference n°3 : the charts should result in a sort of 'smooth' graph. Those jumpy charts will lead to faulty interpolations.
And finally: I think it is necessary to have a known point at the chart where the line buckles. This is missing in many cases. This will lead to faulty interpolations between the 2 surrounding points.
RE: differences between charts and graphs
The ASME Code Committees are volunteers who usually have full-time jobs, so don't get all bent out of shape is there is an error - report it and move on.
RE: differences between charts and graphs
Read Appendix 4 for preferred format of the inquiry, but rest assured that your concerns will be addressed even if you don't follow the format exactly.
As TGS4 pointed out, the Code folks are volunteers, so consider joining in the volunteer effort and coming up with a correction which can be easily implemented.
jt
RE: differences between charts and graphs
I'll send this to the right person.
But how about the second part of this issue?
Is it allowed to use (until corrected by ASME) my own corrected tables? Of do we need to keep working with faulty values?
RE: differences between charts and graphs
This is where "engineering judgment" comes to play. If you believe the tables in ASME are incorrect and your corrected tables are MORE conservative than ASME, I would use the conservative one.
Cheers!
RE: differences between charts and graphs
jt