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Skillet (Paddle Blind) Thickness Calculator

ASME VIII UG-34 · Spectacle Blind · Line Blank

Paddle Blind Thickness per ASME VIII UG-34
Calculates minimum thickness for skillets (paddle blinds), spectacle blinds, and line blanks used for positive isolation in piping systems. Based on flat plate bending under uniform pressure per ASME Section VIII Div 1.

Design Parameters

psig
psi
Per ASME II Part D: S = SMYS ÷ 4 at design temperature
in
in
Added to the minimum thickness; typical 1/16″ (0.0625) to 1/8″ (0.125)

Formula (ASME B31.3 §304.5.3)

t = d × √(C × P / S) + CA
t = Min. Thickness (in)
d = Inside Diameter (in)
C = Attachment Factor
P = Design Pressure (psig)
S = Allowable Stress (psi)
C-Factor (edge coefficient):
0.1875 = Line blank (ASME B31.3 §304.5.3 / API 590 / B16.48)
0.30 = Flat cover (ASME VIII UG-34, simply supported — conservative)
0.33 = Welded or integral edge
Note: B16.48/API 590 manufactured-blank tables are built on the B31.3 0.1875 value; UG-34's 0.30 is the more conservative flat-cover basis.

📚 Learn the Theory

Detailed guide to blind flange design per ASME VIII, flat plate stress analysis, and material selection for line blanks.

Read Engineering Guide →

About This Calculator

Calculates minimum thickness for skillets (paddle blinds), spectacle blinds, and line blanks per ASME Section VIII UG-34.

Key Applications:

  • Paddle Blind: Solid plate inserted between flanges for positive isolation
  • Spectacle Blind: Figure-8 with solid/open sections that can be rotated
  • Line Blank: Temporary or permanent isolation per ASME B16.48

Common Materials:

  • A105: S = 17,500 psi (standard forging)
  • A350 LF2: S = 17,500 psi (low temp)
  • A694 F60/F65: High-yield pipelines
  • A182 F316: S = 16,700 psi (sour service)

Code References:

  • ASME Section VIII Div 1, UG-34
  • ASME B16.48 (Line Blanks)
  • API 590 (Steel Line Blanks)

Frequently Asked Questions

What is skillet (blind flange) thickness calculation?

Line-blank (skillet) thickness is calculated per ASME B31.3 §304.5.3 — the same basis used by the API 590 and ASME B16.48 manufactured-blank tables. The calculator determines the minimum required thickness from design pressure, blank inside diameter, allowable stress, and corrosion allowance, and also offers the more conservative ASME VIII UG-34 flat-cover basis.

What ASME formula is used for skillet thickness?

The calculator uses the ASME B31.3 §304.5.3 blank formula t = d × √(3P / 16SE) + c, i.e. t = d × √(C × P / S × E) + CA with C = 3/16 = 0.1875, where d is the blank inside diameter, P is design pressure, S is allowable stress, E is joint efficiency, and CA is corrosion allowance. A conservative ASME VIII UG-34 flat-cover basis (C = 0.30) and a welded-edge basis (C = 0.33) are also selectable.

What is the corrosion allowance for a skillet blind?

Corrosion allowance is added to the calculated minimum thickness to account for material loss over the vessel's design life. Typical values range from 1/16 inch to 1/8 inch depending on service conditions.

When would you use a skillet blind in piping?

Skillet blinds (paddle blinds or spectacle blinds) are used to positively isolate process piping for maintenance, turnarounds, or to block flow in one branch of a piping system. They are sized per ASME VIII UG-34.

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