ASME hydro test pressure

[libn999]

Hello,

I request some light on this topic that is widely discussed.

ASME code specifies the minimum test pressure as 1.3 times the MAWP at test temperature.



I have seen in general practice, engineers using 1.5 times the MAWP at the design temperature, claiming it will be satisfying the ASME requirement (mentioned above) at the same time it wont let the stress go above the yield limit.



But is it true? there could be some cases when this general practice pressure values going less than the ASME minimum limit?





Libin

 

[metengr]

In general, hydrostatic test pressure used on boilers or pressure vessels during fabrication must be performed at ambient temperature and within the range (1.3 to 1.5) stated in the construction code. Yes, it is true. There is margin against bulk yield during hydrostatic testing performed at ambient test temperature for boiler and pressure vessel materials.

 

[david339933]

Minimum Test pressure per UG-99(b) is 1.3 x MAWP at Design Temp. x lowest ratio of S at test temp to S at design temp.

 

[TGS4]

First things first, you need to be a little more specific when you say "ASME Code". There are many Sections and Divisions, all of which have different requirements.

I'm guessing that by referring to a factor of 1.3 (and that you are posting in a Boiler and Pressure Vessel forum), that you are discussing pressure vessels fabricated to ASME Section VIII, Division 1. In that case, the test ratio is actually 1.3 times the lowest stress ratio - depending on the design temperature this ratio could be as high as 6.5.

 

[SnTMan]

6.5? typo, I hope

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[libn999]

Yes. I mean ASME Section VIII Div 1 UG-99

Let me tell what I understand from the code book.

Ultimately we are using the stress value at the test temperature to find the test pressure. Because the (b) has a correction factor to bring the stress value to the test temperature.

So if I multiply the Maximum allowable pressure for this stress value, with 1.5, I will reach the pressure that create the yield stress on the walls right? ( Because Yield/1.5 is the Allowable stress value)

So how can I run the pressure test with this 1.5 times of the design pressure x LSR? It might distort the vessel right?

 

[TGS4]

Not a typo, but not current. There used to be a limit of 6.5 on the LSR. That no longer exists in UG-99, which has no limit to LSR.

 

[TGS4]

If your material allowable stress is governed by ultimate, a factor of 1.5 might still remain below the minimum-specified yield.

 

[libn999]

TG4,
can you please explain. Allowable is calculated by yield/1.5 right? So 1.5 times the design pressure will take the allowable right back to the yield right?

 

[david339933]

Allowable = lesser of UTS/3.5 or Yield/1.5

 

[Vikko]

Considering ASME BPVC VIII Div 1 Edition 2017.

The definition in Appendix 3 for:
- MAWP maximum allowable working pressure: S in HOT and CORRODED condition
- DP design pressure
- CTP calculated test pressure: S in COLD and NEW condition
- UG-98 definition of MAWP
- UG-99(b) definition of LSR
- Endnote 36: "The MAWP may be assumed to be the same as the DP when calculations are not made to determine the MAWP."

It is possible to choose between 2 options for the calculation of the test pressure, base on UG-99(b) (MAWP) or UG-99(c) (CTP).

Based on UG-99(b): (minimum)
TP >= 1.3 * LSR * MAWP
Or for Endnote 36: HTP >= 1.3 * LSR * DP (which is the lower)

Based on UG-99(c): (special)
TP = 1.3 * CTP

Based on UG-99(d):
There is no maximum test pressure defined. However, in case TP > 1.3 * CTP, the inspector could refuse the vessel if it is deformed because of the hydrostatic test pressure is too high !!!