Test pressure of PN flanges x 1.5 design pressure...........where does this come from??? 2

[JBNKL]

I have a question on design pressure of PN flanges and test pressure.

My understanding is that a PN10 flange can take 10barg design pressure, and that you can test the flanged pipe to 1.5 x the design pressure. PN10 flanged pipe can take up to 15barg test pressure. Similar for PN16 flanges they can take 16barg design pressure, and 1.5 times the design pressure, so 16+8 = 24barg maximum test pressure.

This is my understsnding, but which code or regulation says you can test Pn flanged pipe to 1.5 times the design pressure?

 

[0707]

ASME B31.1 Power Piping
ASME B31.3 Process Piping
ASME B31.5 Refrigeration Piping

 

[XL83NL]

It comes from me. No honestly, it does. (Well, I technically might not have invented but I’m a strong advocate;-)).

There’s an unwritten rule practice to make most (ASME B31) pipespecs flange limited. You then test to 1.5 the ambient flange rating. This is allowed per B16.5. The above is at least how we do it.
Now, we have a lot of customers that require EN 1092-1 (thus PN designated) flanges. But going all the way EN 13480 is a pain in the…. We then make our specs and design to B31 (in our case, B31.3), and swap the B16.5 flange with EN 1092-1.
The principle of a certain ratio of allowable stress vs yield is roughly the same under EN. That analogy allows us then to apply that same principle to this PN flange. There’s just not a specific paragraph in this subject, similar to the B16.5 analogy, in the EN flange standard.
So, regarding what the OP wrote isn’t technically correct. It’s correct for B31/B16, but not so much for EN. The ratio for testing in EN, if I’m not mistaken, is a 5% allowance to the 1.5 limit. Take 1.5 divided by 1.05 et voila, there you have the magical factor of 1.43 from the PED. I haven’t found this out, there’s an old topic on that here at ET

Huub
- You never get what you expect, you only get what you inspect.

 

[JBNKL]

Hi Huub,

We did a little more digging today, below is from an email summary:

ASME B31.3-2016 Process Piping

Section 345.4.2 Test Pressure, page 124

Except as provided in para. 345.4.3, the hydrostatic test pressure at every point in the metallic piping system shall be a follows:
(a) Not less than 1.5 times the design pressure.
(b) When the design temperature is greater than the test temperature, the minimum test pressure, at point under consideration, shall be calculated using eq. (24).

Pt = 1.5 PSt/S

So if the AMSE flange rating is 10 barg (ASA150lb flange) the ‘flange rating design pressure’ is 10 barg and ‘flange rating test pressure’ would be 15 barg.

As an example if the same flanges and pipe were subject to ‘process design pressure’ 8 barg, as an example limited to upsteam relief valve 8 barg set pressure. Then the test pressure would be (8 x1,5 = 12) 12 barg.

Since we do not calculate the stress we only use (a) 1.5.


EN 1092-1:2018 Flanges and their joints – Circular flanges for pipes, valves, fittings and accessories, PN designated – Part 1: Steel flanges

Section E.3.2.1 Flanges type 11, type 04 with type 34, type 05, page 104

f) Nominal design stress:
1) at operation 140 MPa;
2) at assembly and testing 200 MPa (Ptest = 1,43 x PN).

This test pressure 1,43 x design pressure, aligns with NNE Specification Pneumatic Pressure Testing of Industrial Metalic Piping -1502.

This means that for PN flanges the test pressure is 1,43 x the design pressure rating.

• PN10 (Pressure Nominal 10 barg) flanges the test maximum test pressure is 14,3 barg.
• PN16 (Pressure Nominal 16 barg) flanges the test maximum test pressure is 22,8 barg.

It should be noted that the ‘process design pressure’ or ‘maximum allowable design pressure’, should not exceed the the design pressure rating of the flange or pipework. Same for any pipework ancillaries.

Cheers

James

 

[r6155]

My comments:
1) You are confused with flange (B16.5 2020) and piping (B31.3 2020)

2) See pressure- temperature rating in B16.5 :depends on material

3) See B16.5
8.1 Flange Test
Flanges are not required to be pressure tested.

4) See B16.5
2.6 System Hydrostatic Testing
Flanged joints and flanged fittings may be subjected to
system hydrostatic tests at a pressure of 1.5 times the 38°C
(100°F) rating rounded offto the next higher 1 bar (25 psi)
increment. Testing at any higher pressure is the respon￾
sibility ofthe user,taking into accountthe requirements of
the applicable code or regulation.

5) Use last edition of ASME

6) ASA is now ASME (AN AMERICAN NATIONAL STANDARD).

7) Example- B16.5 flange class 150 group 1.1 material: the working pressure is 285 psi at 100°F (38°C). and may be subjected to 285 x 1.5= 427 psi

Regards