Hello again Nixon123,
Please learn to use the powerful “SEARCH” function that this discussion forum provides. You will find that MANY of the questions that trouble you have been previously discussed here in detail. Judging from your questions you will have to do a lot of studying to “catch up” with the “basic concepts”.
You cannot perform competent piping design and stress analysis unless you completely understand several basic concepts.
You must totally understand the beam theory method of structural analysis. The B31 Codes for Pressure Piping are based upon beam theory methods. For piping flexibility analysis, stresses are calculated as the bending moment divided by the pipe section modulus (the general form is M / Z). If the beam is other than a straight piece of pipe, a stress intensification factor (SIF – using the symbol “i”) is included making the equation for calculating the stress (or stress range) M * i / Z. The stress intensification factors that are appropriate for various piping components came from fatigue testing of various piping components and they can be found in appendices “D” in B31.1 and B31.3. To find the bases for the ASME B31 Pressure Piping Code SIF’s it would be good to read the Markl Papers that are found in the book “Piping Engineering” that was published by Tube Turns Company. The book can be found on the Internet.
As per ASME B31.1 what is meant by "STRESS RANGE"?
1) Why it should be called as stress range?
You must completely understand the difference between primary and secondary stresses and why the piping Codes evaluate these stresses differently. This leads directly to the concept of using “the total range for calculating secondary stress” and the Code allowable stress range. Please understand that in piping structural analysis, the concept of thermal expansion and contraction stresses (secondary stresses) is all about alternating loadings and the effect of fatigue. We consider the piping “as installed” at the ambient installation temperature to be “without expansion stress”. When the piping contracts as the temperature falls from the “ambient installed temperature” (perhaps winter weather and out of service) to the coldest temperature, it will experience bending stresses results throughout the piping system. When the piping expands as the temperature increases from the “ambient installed temperature” to the highest operating temperature, it will experience bending stresses results throughout the piping system. The entire RANGE of stresses from the coldest temperature to the hottest temperature must be considered and compared to the Code allowable stress range. Read this previous discussion:
http://www.coade.com/ubb/Forum1/HTML/000057.html .
And maybe this one:
http://www.coade.com/ubbthreads/ubbthrea...ch=true#Post693and:
http://www.coade.com/support_discussion.asp2) We all know Thermal Expansion Stress range equation as per ASME B31.1:
Sa = f(1.25Sc + 0.25Sh),what is the basis for this equation and how it is
derived from fundametals.
3)Why Sc is multiplied with higher factor as "1.25" and Sh with lower factor as "0.25"?
The equation that you cite:
Sa = f * (1.25 * Sc + 0.25 * Sh)
IS NOT the equation for calculating the Thermal Expansion Stress Range. Rather it is the equation for calculating the Code allowable stress range. This equation for the “allowable” provides the stress range that you must compare to the calculated (by Caesar II) stress range as given in paragraph 104.8.3 of B31.1:
SE = i * Mc / Z
Note that the expansion (or displacement) stress range, SE, must be less than (Sa + f * (Sh – Sl))
The expansion (displacement) stress RANGE, SE, that you calculate (and compare to Sa) is the range of stresses from the coldest temperature to the hottest temperature (e.g., consider a piping system that is installed at 70 degrees F - if the coldest temperature is 20 degrees F and the hottest temperature is 500 degrees F, the temperature range to be considered in the SE equation is 480 degrees F (70 to 20 = 50 plus 70 to 500 = 430, therefore the sum (range) is 480 degrees F).
As I mentioned, you can find many of the answers that you seek here at this discussion forum simply by searching the archive of previous discussions, for example:
http://www.coade.com/ubbthreads/ubbthrea...h=true#Post1252Also, search and find the archive of COADE “Mechanical Engineering” newsletters because our esteemed colleague John Luf and many others (including our COADE board moderators) have written many articles for these newsletters that will help you to understand the “basic concepts”.
There are some good books available that may make your study easier:
Process Piping: The Complete Guide to ASME B31.3. Second Edition. Charles Becht IV. ASME Press
http://catalog.asme.org/books/PrintBook/Process_Piping_Complete_Guide.cfm The Fourth edition of the CASTI Guidebook to ASME B31.3 - Process Piping
The authors are Glynn Woods and Roy Baguley.
http://www.casti.ca/books_ebooks/B31_3.html A new book from ASME Press:
Applying the ASME Codes: Plant Piping & Pressure Vessels (Mister Mech Mentor, Vol. 2) by James A. Wingate
http://catalog.asme.org/books/PrintBook/Applying_Codes_Plant_Piping.cfmAnd this one:
Piping Systems and Pipelines : ASME Code Simplified (Hardcover)
by Phillip Ellenberger
http://www.amazon.com/Pressure-Vessels-ASME-Code-Simplified/dp/0071436731Be a good student.
Regards, John