Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

  • Congratulations TugboatEng on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Allowable Stress for Boiler Design

Status
Not open for further replies.

aida2011

Mechanical
Joined
Jun 25, 2013
Messages
62
Location
MY
Dear all,

I have a question on allowable stress.

I can understand how the allowable stresses are obtained from Ultimate tensile strength (UTS/3.5) and yield strength (YS/1.5). However, I do not understand how allowable stress is obtained by using creep value.

Please help.

Thanks very much,

Aida Hannah
 
Please review ASME Section II, Part D, Mandatory Appendix 1. The information is there to determine allowable stress value for the time dependent regime below.

(b) At temperatures in the range where creep and
stress rupture strength govern the selection of stresses,
the maximum allowable stress value for all materials is
established by the Committee not to exceed the lowest
of the following:
(1) 100% of the average stress to produce a creep
rate of 0.01%/1,000 hr
(2) 100Favg% of the average stress to cause rupture
at the end of 100,000 hr
(3) 80% of the minimum stress to cause rupture at
the end of 100,000 hr
 
and there is also a weld creep strength reduction factor applied if there is a longitudinal seam weld or a weld that is not totally a true circumferential butt weld ( such as a saddle weld). A conservative practice may be to also consider the weld creep strength reduction factor on all welds that also restrain other continuous secondary loads, such as gravity loads.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
 
Only one point to add, weld strength reduction factor is not applicable for carbon steels as per PW-26 of Section I

Javed Nasir
Inspection Engineer
Technip-France Abu Dhabi
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top