Example

The whole operation of the joint will need to be checked - leakage tendency as indicated by 'm' and 'y' factors, fatigue of the bolts, and so on.

Dimensions & initial loading
The width of the gasket here is (150-125)/2 = 12.5 mm. AS 1210 table 3.21.6.4(B) states that the effective width, allowing for rotation etc, is 2.52√(width/2) = 6.3 mm.
Gasket OD is 150 mm, so gasket effective ID is 150- 2 x 6.3 = 137.4 mm, and gasket effective area is A_g = π( 150² -137.4² )/4 = 2844 mm².
The effective area inside the gasket which is subjected to fluid pressure is A_i = 137.4² π/4 = 14 830 mm².
Bolts' proof load F_p = 245 x 380 = 93 kN
Assume tightening to 75% proof, then total initial tightening load is F_i = 8 x 0.75 x F_p = 560 kN.

Stiffnesses & joint factor
On the basis of a single bolt and the gasket associated with it . . . .

Bolt

Grip = 2 x 35 + 4 = 74 mm. Assume two exposed threads and head/nut height = 0.8 x 20 = 16 mm
1/k_b = Σ L/AE = [ (74 -2 x 2.5 +0.5 x 16)/π x 10² + (2 x 2.5 +0.5 x 16)/245 ]/207 ;     k_b = 694 kN/mm

Joint

Gasket area associated with one bolt A_g = ¹/₈ of 2844 = 356 mm²
Table 4 quotes limits for the stiffness of the gasket material 270 to 1800 MPa/mm, or, in units of force ( multiplying by A_g= 356 mm²) 96 ≤ k_g ≤ 640 kN/mm.
It is anticipated that a larger value will be more appropriate, but we'll persist with two extreme values using {} to show results for the smaller stiffness. So select estimated gasket stiffness of k_g = 600 kN/mm   { 100 kN/mm }.
The portion of each flange in direct compression will be modelled as a 35mm long conical frustum using ( 4)
k_f = 207 x 20 x (0.702 +0.654 x 20/35)/(1 -0.12 x 20/35) = 4780 kN/mm
This is so much greater than k_g that the approximation inherent in applying the frustum model in this case should not carry over into the overall joint stiffness. So for the two flanges and the gasket in series in the joint :
1/k_j = 2/k_f +1/k_g = 2/4780 +1/600 ;     k_j = 480 kN/mm   { 96 kN/mm }

Gasket stress limitations
Based upon whole gasket . . . .
From Table 3, y = 69 MPa and m= 3.0 for a spiral wound asbestos filled gasket.
The initial gasket stress is F_i/A_g = 560/2844 = 197 MPa > y, so OK.
Check crushing - lacking any recommendations, presume a limiting stress of 2y = 138 MPa ( based on   total not effective gasket area ). Based upon this area, the initial ( ie. maximum ) stress on the gasket is 560 x 4/π( 150²-125² ) = 104 MPa < 2y and so crushing should not be a problem.

Now consider gasket stress when full fluid pressure of 7.5 MPa is applied. From ( 3b) with external fluid load ( or   hydrostatic load ) of P = p_fluid A_i = 7.5 x 14830 = 111 kN
F_j = F_i - ( 1 -C ) P = 560 -(1-0.59) x 111 = 514 kN   { 547 kN }
which corresponds to a gasket stress of p_g = F_j /A_g = 514/2844 = 181 MPa   { 192 MPa }
Ratio p_g /p_fluid = 181/7.5 > m = 3.0 so this criterion is satisfied and the gasket should not leak.

Bolt fatigue
Based upon a single bolt . . . .
From Table 2, S_u = 0.5 GPa, so S_e' = ( 0.55 -0.088 x 0.5 ) x 0.5 = 253 MPa
Assuming rolled threads, K_f = 2.2 ( Table 6 ) and so S_e = S_e'/K_f = 253/2.2 = 115 MPa
σ_i = F_i /A_s = 560/8 x 245 = 286 MPa
σ_a = CP/2A_s = 0.59 x 111/2 x 8 x 245 = 17 MPa   { 25 MPa }

Applying ( 6a), the safety factor for the load on the bolts themselves ( F_b) is
1/n = σ_i /S_u + σ_a (1/S_u + 1/S_e ) = 286/500 +17 x ( 1/500 +1/115) ;     n = 1.33   { 1.19 - note effect of small k_j }
Alternatively, applying ( 6b) for the safety factor on fluid pressure loading ( P) against bolt fatigue failure
1 = σ_i /S_u + n σ_a (1/S_u + 1/S_e ) = 286/500 + n x 17 x ( 1/500 +1/115) ;     n = 2.35   { 1.60 }

All-in-all, the joint is satisfactory as it stands. The bolt class is therefore suitable.