As per UG-39(b)(1) : Reinforcement Area Required=0.5*Opening Diamater*t.

t is the thk of flange for operating condition, not for seating condition.

If we go for UG-39(d), then the multiplier 2 shall be for operating condition only.

Please clarify.
We have noticed that PV Elite is not doing this way for both option(1) by adding Nozzle or (b) by adding opening diameter ?

Can you clarify this ???

Hi Ketan,

When determining the area required for reinforcement, the value of the requried thickness 't' is computed with consideration to both the operating and seating conditions as shown below:

Tangential Flange Stress, Flat Head (UG-34), Operating [STo]:
= 1.9 * Wm1 * hG * Bcor/(t² * G) + C * Z * Peq * G²/t²
= 1.9 * 69448 * 1.5757 * 1.0000 /(1.7550² * 26.3486 ) +
0.30 * 1.0000 * 100.00 * 26.3486²/1.7550²
= 9324.12 psi

Tangential Flange Stress, Flat Head (UG-34), Seating [STa]:
= 1.9 * W * hG * Bcor / (t² * G)
= 1.9 * 266974 * 1.5757 * 1.000 /(1.7550² * 26.3486 )
= 9848.80 psi

The greater of the two computed thicknesses is used when determining the required area of reinforcement. PV Elite does not address UG-39(d)(1). You would have to modify the C factor input to suit your particular sketch/requirement. For single openings in flat heads, PV Elite addresses UG-39(d)(2) via Tools->Configuration. PV Elite does address multiple openings in flat heads. Checks for multiple nozzles in flat heads are shown in the nozzle summary report.

Dear Scott,
Please refer the related pages from D R Moss, where it is mentioned that t is the thickness of operating condition only. Plaese clarify the need of maximum thickness consideration from seating thickness and operating condition. or is there any error in the pages from D R Moss / ASME CODE ?

Hi Ketan,

I certainly understand your point; that being the pressure is zero during the seating case. Therefore it seems reasonable to use the required thickness during the opertaing case.

However, we should review the definition of t from UG-34(b) and it is:

t = minimum required thickness of flat head or cover

The required thickness is the greater of the values between operating and gasket seating. There is a Code Case that seems to shed some light on this:

Interpretation.- VIII-1-83-181
Subject: Section VIII, Division 1; UG-34 and UG-39
Date Issued: October 27, 1983
File: BC83-315

Question: A flat head of the type depicted in Fig. UG-34 sketch (j) or (k) of Section VIII, Division 1, is to have reinforcement as required by UG-39(b). Since the opening in the blind flange is equal to or less than, half the head diameter, is it appropriate to use Formula (1) from UG-34(c)(2) instead of Formula (2)?

Reply: No. Formula (2) of UG-34(c)(2) is required for this case.

Hopefully this helps.

Dear Scott,

Please find the attached page from D R Moss, which says that

Reinforce ment requirement= 0.5 * opening diameter * thickness in operating condition.


Can you please send the reply that in the UG-39(b)(1)in the formula for reinforcement requirement calculation which thickness to be used either operating thickness or gasket seating thickness ??? or hogher of both ???

In the sent interpretation by you, it says that both the thickness needs to be calculated. We are also agree with the same. But for the reinforcement checking the thickness is to be used as operating case thickness.This interpretation is not for the UG-39(b)(1) case.