CR4 - Comment: Re: What is the Acceptable Tolerance on 2:1 Semi Ellipsoidal Ellipsoidal Dish Head Page Page 1 of 2
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Re: What is the Acceptable Tolerance on 2:1 Semi Ellipsoidal Dish Head
Galala
08/26/2011 1:45 PM
Guru
Formed Heads Tolerances, UG-81 (for torispherical, toriconical, hemispherical and ellipsoidal heads):
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· Tolerance (deviation* (deviation*) of inner diameter outside of the specified shape ≤ 1.25 % D · Tolerance (dviation* (dviation*) of inner diameter inside of the specified shape ≤ 5/8 % D Where, D = Nominal inside diameter of the vessel shell at point of attachment. * Such tolerance (deviation) shall be measured perpendicular to the specified shape and shall not be abrupt. Join Date: Feb 2007 Location: Cairo, Egypt Posts: 1746 Good Answers: 239
Very important to know the acceptance criteria and "How do you apply the tolerance for dished heads as per UG-81": ● For code items like dished heads (especially that intended to be used in vessels need to be certified U-stamp), it is mandatory by the code to prepare a material receiving report, and that report shall include dimensions checking/verification checking/verification prepared by a specialist like as inspector or vessel engineer. ● And checking head dimensions (as detailed at the attached drawing) is very very important to satisfy yourself that all tolerances are within the limits of UG-81. ● The procedure depends on dividing the x-axis of the head into equally spaced intervals (may be 50 or 100 mm). ● The specialist who preparing the material receiving report must measure/calculate measure/calculate and/or draw/plot the 4 curves:
1. The standard ellipsoidal 2:1 curve using equation: y = SQRT [h2 - (h2/a2) x2], where, SQRT = Square Root, √ a = D/2 h = inner depth of head at middle (in case of ellipsoidal head 2:1, h= D/4) D = head inner diameter x = axis x y = axis y 2. The curve of allowed outer tolerance based on + 1.25 % D, based on standard curve, 3. The curve of allowed inner tolerance based on - 5/8 % D, based on standard curve, then 4. Plotting the actual curve of supplied head.
CR4 - Comment: Re: What is the Acceptable Tolerance on 2:1 Semi Ellipsoidal Dish Head Page 2 of 2
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..................................... ● The actual locus of curve of supplied head must be located in between the two curves of allowed inner (black) and outer (red) tolerances, otherwise the head shall be rejected.
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