Thickness of Torispherical Head
Thickness of Torispherical Head
(OP)
Hi, I am working with a vessel having torispherical top head. the vessel has some thinning in the head and when I went to calculate the MAWP it came out very low. in fact the original thickness from data report according to my calculations are not meeting the design MAWP. we operate the vessel lower than the MAWP so that's a good thing. but I want to make sure I am calculating the right way before de-rating the vessel. below are the calculations:
Given as per data report: Tori spherical Head
Material: SA-516 Gr. 70;
OD= 54”
Crown radius= 54"
Knuckle radius= 3.24"
E=0.85
Min thickness= 0.24”
MAWP= 100 Psi @ max temperature 500 F
From Sec II stress tables: S= 20.0 Ksi (SA516 Gr 70 @ 500 F)
From UG-32: t= 0.885PL/(SE-0.1P)= 0.885*100*54/(20000*.85-0.1*100)= 0.28"
P= SEt/(0.885L+0.1*t)= 20000*.85*.24/(0.885*54+0.1*0.24)= 85.33 Psi as opposed to design MAWP of 100 mentioned in data report.
I forced myself to assume that the manufacturer may have assumed a higher stress value but as per UG-32e limits the max stress value of 20000 psi for torispherical heads..
so I would appreciate any comments as to what is happening here or anything can be done? otherwise I will have no option but to de-rate the vessel. thanks in advance.
Given as per data report: Tori spherical Head
Material: SA-516 Gr. 70;
OD= 54”
Crown radius= 54"
Knuckle radius= 3.24"
E=0.85
Min thickness= 0.24”
MAWP= 100 Psi @ max temperature 500 F
From Sec II stress tables: S= 20.0 Ksi (SA516 Gr 70 @ 500 F)
From UG-32: t= 0.885PL/(SE-0.1P)= 0.885*100*54/(20000*.85-0.1*100)= 0.28"
P= SEt/(0.885L+0.1*t)= 20000*.85*.24/(0.885*54+0.1*0.24)= 85.33 Psi as opposed to design MAWP of 100 mentioned in data report.
I forced myself to assume that the manufacturer may have assumed a higher stress value but as per UG-32e limits the max stress value of 20000 psi for torispherical heads..
so I would appreciate any comments as to what is happening here or anything can be done? otherwise I will have no option but to de-rate the vessel. thanks in advance.





RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
That could be the mistake I am making. Data report shows the joint efficiency for type 1 (long) @ 70% and type 2 (Girth)@ 85%, but could it be only for the shell? not sure what kind of radiography was done for the head
RE: Thickness of Torispherical Head
Also, if the thinning is limited to the crown portion (away from the knuckle) you can always use the spherical formula to calculate minimum thickness.
RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads
RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
If this were a new vessel, I would apply Code Case 2695 and use the VIII-2 rules. Even if there were a weld joint efficiency factor of 0.85, this would reduce the crown allowable pressure to 150.8psi.
I don't see the problem here.
RE: Thickness of Torispherical Head
I do however tend to agree that CC2965 is the right approach for something new.
RE: Thickness of Torispherical Head
RE: Thickness of Torispherical Head
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes and launchers for fun rides
http://www.levitans.com : Air bearing pads
RE: Thickness of Torispherical Head