Swedish standard – RN78

The internal pressures are calculated by using the following formula:

Where:

P Internal pressure (Mpa) (* 10 => bar)
tmin Min wall thickness (mm)
S Allowable stress (S = Rp0.2/1.5) (MPa)
OD Nominal outside diameter (mm)
ID Inside diameter (OD-2×tmin) (mm)
m
Coefficient depending on the quota OD/ID
m = 1 for OD/ID <= 1.6
m = 0.25×OD/ID+0.6 for 1.6 < OD/ID <= 2.0

Attention: The pressures on these pages are given only as guidance. Dimensioning of piping systems also depend on other factors like external forces, thermal stresses, dead weight etc. Furthermore the design must be made according to regulations from local authorities and approved accordingly. For tubes in pressure vessels and boilers it is important to consider standards like TKN (Tryckkärlsnormer) 1987 and PSN (Pannsvetsnormer).

Allowed maximum wall thickness and outer diameter:
8 mm 10 mm 20 mm 24 mm OD max. mm
3RE60 3R12
3R60™
3R65
8R30/6R35
8R40
8R70/5R75 
Sanicro® 28
2RK65™
SAF 2304®
SAF 2507®
SAF 2205™ Sanicro® 28
SAF 2304®
SAF 2205™
SAF 2507®
260
260
260
273
Proof strength Rp0.2 (MPa)
Sandvik SS 20°C 100°C 150°C 200°C 250°C 300°C 350°C 400°C
3R12*1) 2352 190 149 134 125 118 112 107 103
3R60™*2) 2353 210 167 152 141 132 126 122 118
3R65*3) 2348 210 167 152 141 132 126 122 118
6R35*4) 2337 210 174 160 150 143 137 133 129
8R40*5) 2338 220 181 167 158 150 145 140 136
5R75*6) 2350 220 187 176 168 161 156 152 148
2RK65™*7) 2562 220 175 165 155 145 135 130 125
Sanicro® 28*8) 2584 220 175 165 155 145 135 130 125
3RE60™*9) 2376 450 370 345 330 325 320
SAF 2304®*10) 2327 400 315 290 275 265 255
SAF 2205™*11) 2377 450 360 335 310 295
SAF 2507®*12) 2328 550 480 445 420 405

(1 MPa = 10 bar)
*1) RN 78. t<=10mm
*2) RN 78. t<=10mm
*3) RN 78. t<=10mm
*4) RN 78. t<=10mm
*5) RN 78. t<=10mm
*6) RN 78. t<=10mm
*7) RN 78. t<=20mm
*8) NGS 1608, March 1990. OD <= 260mm, t<=10mm.
*9) NGS 1604, Sept.1983. t<= 8mm. Tmax 300°C
*10) NGS 1607, March 1992. OD <= 260mm, t<=20mm. Tmax 300°C
*11) NSG 1606, Nov 1998. OD <= 260mm, t<=24mm. Tmax 280°C. Rp0.2 is 290 MPa at 280°C, for not welded constructions
*12) NGS 1609, March 1998. OD <= 273mm, t<=20mm. Tmax 250°C