API 6A App. D RTJ Torque Values
API 6A App. D RTJ Torque Values
(OP)
How are API 6A App. D recommended torque values applied to an RTJ. Am I to perform a calculation similar to ASME Sec 8 Div 1 App2 to determine bolt stress? API 6A, APP D recommends 40 and 52.5 ksi bolt stress, but for what application?
Rick
Rick





RE: API 6A App. D RTJ Torque Values
This is not the same as the design allowable stress of .83Sy which must be calculated based on the thread root area and take into account all load conditions.
RE: API 6A App. D RTJ Torque Values
RE: API 6A App. D RTJ Torque Values
For B7 & L7 studs Sy=105 ksi, make up stress 52.5 ksi
For B7M & L7M studs Sy=80ksi, make up stress 40 ksi
RE: API 6A App. D RTJ Torque Values
Also Sy changes with diameter as per ASME PV code. Therefore these tables would only apply to a range of sizes.
Rick
RE: API 6A App. D RTJ Torque Values
The ASME B&PVC does not apply to API 6A except where it is specified by API 6A.
RE: API 6A App. D RTJ Torque Values
Rick
RE: API 6A App. D RTJ Torque Values
There are three different styles of API flanges as well as some common proprietary styles. Some will bolt to contact most do not.
RE: API 6A App. D RTJ Torque Values
RE: API 6A App. D RTJ Torque Values
RE: API 6A App. D RTJ Torque Values
Weld neck and flange thickness dimensions are similar between the ASME and API flanges.ASME has a bit larger OD.
I think bolting this joint to 14,000 psi bolt stress is too low.
Rick
RE: API 6A App. D RTJ Torque Values
Also note the B16.5 and 6A dimensions for some flanges are similar up to class 1500 (6A 5000 psi) but not above that. Also material requirements for the two specs are considerably different.
RE: API 6A App. D RTJ Torque Values
Rick
RE: API 6A App. D RTJ Torque Values
Minimum required bolt load at operating condition = pressure end load + gasket load
Wm1 = H + Hp = (.785*G*G*P) + (2*b*3.14*G*m*P)
G gasket pitch = 5.000"
P operating pressure = 6000 psi (assumed pressure rating, pressure ratings vary between 2000 psi and 6250 psi at room Temp and decrease with temp increase)
b gasket seating width = w/8
w gasket width = .500
m gasket factor = 6 (assumed value for rough calculation mild steel would be 5.5 stainless would be 6.5)
Maximum bolt load
W = (Am + Ab)* Sa/2
Am = Wm1/Sb
Sb = Sa for room temp but will decrease with temp increase
Ab = Area of bolts under root = 7.59 in*in
Sa = yield stress of bolt at room temp = 105 ksi
Divide Wm1 & W by 8 to get load per bolt.
I didn't bother to check the minimum load for gasket seating because it rarely is the controlling factor for RTJs
but if you want to
Wm2 = 3.14*b*G*y
y = gasket seating stress = 18 ksi to 26 ksi
6A can get away with using 1/2 the bolt yield as bolt load because the minimum yield stress for 6A flanges is 45 ksi for weld necks and 60 ksi for everything else (75 ksi for 15,000 psi and above). ASME flanges are made from every material you could think of and bolt loads should be calculated according to the material and temperature conditions.
RE: API 6A App. D RTJ Torque Values
Your advice has been helpful.
I agree with your internet comment, and it's up to all of us to verify the opinions and advice we are receiving.
Rick
RE: API 6A App. D RTJ Torque Values
an impirical value for bolt tensioninig
( I think it is 25000 psi / (sqrt(bolt diam.) ).
API 6A - Appendix D gives also the bolt tensioning force based on 50% of the yield.
In both cases the bolt tensioning is translated into a torque and this is function of the lubricant, diameters, pitch...
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The question which bother me is what is the relation between this 50 % yield = 360 N/mm2 and Sa =172 N/mm2 for A-193 B7 bolt < 2".
This Sa , as explained above is used in
W = (Am + Ab)* Sa/2
Why are we talking about 2 bolt stresses??
API 6A Appendix D has nothing to do (in my opinion, I maight be wrong!) with ASME!!!
RE: API 6A App. D RTJ Torque Values
quote : Sa = yield stress of bolt at room temp = 105 ksi
End of quote.
Sa: design stress value taken from, for instance B31.3 table A-2
For A-193 B7 or A 320 L7 :
Sa 25 ksi = 172 N/mm2 for d< 2 1/2"
for up to 400 Fahr.
Sa = Tensile strength ( and not yield ) divided by FIVE
I believe derivation of bolt stresss is given in ASME VIII div.1 appendix P