Engineering calculator reviewed for preliminary design use · Last updated: March 2026
Uses Dg=D+20 mm, width 3 mm, Ag=πDg·3, σg=max(y,mP), Wg=Agσg/1000, Hp=π(D/2)²P/1000, W=(Wg+Hp)SF, n=max(4,ceil(D/25)×4), Ab=(W/n)1000/Sb, and db=√(4Ab/π). Gasket (m,y MPa): spiral wound (3,69), rubber (1,2.8), PTFE (2,14), metal (6.5,200). Base Sb is 140 MPa for carbon/stainless steel and 170 MPa for alloy steel; above 100 °C, Sb=Sb,base[1−min(0.30,(T−100)/1000)]. It does not select flange class, standard thread, or torque.
What this calculator is used for
This preliminary estimator calculates gasket stress, total bolt load, bolt count,
and a continuous required bolt diameter using a deliberately simplified geometry
and material model.
Typical engineering use cases
Early comparison of load and bolt-size sensitivity
Explore effects of gasket type, pressure, temperature, and safety factor
Governing equation and methodology
For nominal size D, the model assumes gasket mean diameter Dg = D + 20 mm and
gasket width 3 mm. Gasket area Ag = π·Dg·3, gasket stress σg = max(y, mP),
gasket load Wg = Ag·σg/1000 kN, hydrostatic end force
Hp = π(D/2)²P/1000 kN, and total bolt load W = (Wg + Hp)·SF.
Here D and Dg are in mm; P, y, σg, and Sb are in MPa; and areas are in mm².
Key parameters include:
Gasket factors (m, y [MPa]): spiral wound (3.0, 69), rubber (1.0, 2.8), PTFE (2.0, 14), metal (6.5, 200)
Bolt count n = max(4, ceil(D/25) × 4)
Per-bolt load wb = W/n, required area Ab = wb·1000/Sb, and continuous diameter db = √(4Ab/π)
For T ≤ 100 °C, Sb = Sb,base. For T > 100 °C, Sb = Sb,base·[1 − min(0.30, (T−100)/1000)]
Engineering assumptions and limitations
Uniform bolt load distribution assumed
Selected flange face does not alter the calculation
No threaded tensile area, flange stress/rotation, external load, or torque model
Practical design notes
The displayed M label is the continuous diameter rounded up to an integer millimetre,
not selection of a standard threaded fastener. The estimator does not select a flange
class or pressure-temperature rating and is not a formal flange design or certification.
Interpretation: These values reproduce the calculator defaults and simplified model. M15 is a rounded continuous diameter, not a standard threaded-bolt selection. The estimate does not determine flange class, rating, torque, flange stresses, or certification.
Common Mistakes & Misuse
Treating nominal size D as a detailed gasket dimension — the model simply assumes Dg = D + 20 mm and width = 3 mm.
Reading the displayed M label as a standard threaded bolt selection — it is only the continuous diameter rounded up.
Assuming the flange-face selector changes the arithmetic; the current simplified model does not use it.
Using the estimate as a flange class, pressure-temperature rating, tightening torque, or formal flange design.
Frequently Asked Questions
What simplifications does the estimator use?
It uses Dg=D+20 mm, width 3 mm, Ag=πDg·3, σg=max(y,mP), Wg=Agσg/1000, Hp=π(D/2)²P/1000, W=(Wg+Hp)SF, n=max(4,ceil(D/25)×4), Ab=(W/n)1000/Sb, and db=√(4Ab/π). Gasket (m,y MPa) values are spiral wound (3,69), rubber (1,2.8), PTFE (2,14), and metal (6.5,200). Base Sb is 140 MPa for carbon/stainless steel and 170 MPa for alloy steel; above 100 °C it is multiplied by 1−min(0.30,(T−100)/1000).
Does the displayed M size select a standard bolt or flange class?
No. It is the continuous required diameter rounded up to an integer millimetre. Thread tensile area, available standard sizes, flange stress and rotation, class ratings, and tightening torque are outside this estimate.
For preliminary estimation and educational use only. Results may depend strongly on assumptions, input data, fluid or material properties, and the range of validity of the underlying equation. Verify critical calculations independently and follow the applicable code, specification, and formal engineering review process before using any result for design, procurement, fabrication, operation, or safety decisions.