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Accounting for Static Head for Hydraulic Vessel TestingHelpful Member!(2) 

nco2612 (Mechanical) (OP)
22 Sep 07 5:43
I am looking for a definitive method/formula for accounting for static head. Vessel design criteria & specified test pressures are vertical at top.
Vessels are too big to test this way in our shop & therefore
test pressures must be adjusted to reflect pressure at base of vessel.
We have presented figures to our client who have indicated we are incorrect in our adjustment but will not elaborate why.
I would to understand better before I challenge our client.
desertfox (Mechanical)
23 Sep 07 7:34
Hi nco2612

Could you elaborate how you tested the vessels and design code your working too, whether theres' temperature involved or not?

Regards

desertfox
Helpful Member!  decode (Mechanical)
23 Sep 07 9:45
nco2612, The Code does not require you add the static head when you test a vertical vessel in horizontal position. Please check attached Interpretation which is still valid.

Interpretation: VIII-1-95-27
Subject: Section VIII, Division 1 (1992 Edition, 1993 Addenda); UG-99(b)
Date Issued: January 12, 1995
File Number: BC94-414
Related Documents:  

Question (1): Does the last sentence of UG-99(b) of Section VIII, Division 1, "All loadings that may exist during this test shall be given consideration," require that the static head that exists in a tower in the vertical position must be considered when determining the test pressure in the horizontal position?

Reply (1): No.

Question (2): Does UG-99 specify in which position a vertical tower must be hydrotested?

Reply (2): No.

Regards,

Decoder.
nco2612 (Mechanical) (OP)
24 Sep 07 4:25
Yes, I am looking for methodology for both ASME & PD5500.
Vessels are designed by our client but we must test in
the horizontal. Design Pressures given are vertical at Top.
Test will be with water at ambient (min 7deg).
Client asks for us as the manufacturer to confirm the pressure horiz but has disagreed with the figures we
presented.
carthago (Mechanical)
24 Sep 07 5:44
ThEre is a specifIand dedicated Annex about this subject with formula and all, it is in

EN13445-
   Part 5
       annex F
prex (Structural)
24 Sep 07 9:00
You should simply add to the specified test pressure the static head corresponding to the height of the vessel filled with water. The test pressure so obtained will be measured at the high point of the vessel when this one is horizontal.
However in this case it becomes necessary to check that no part in the vessel will be overstressed during the test, especially parts that are in the upper portion of the vertical vessel. This check may only be done by the designer (and in my opinion also the test pressure should be calculated by the designer).

prex
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gr2vessels (Mechanical)
24 Sep 07 19:26
nco2612,
The hydro test pressure is calculated by the software used for the design of the vessel. You, as a fabricator not responsible for the design of the vessel, you were suppose to be given the test pressure by your Client. Did you agree to become part of the design liability, by accepting to provide the hydro testing design to your Client? Who's calculated or nominated the MAWP, which enables the calculation of the hydro test pressure? Refer to UG-99(b) below:
(b) Except as otherwise permitted in (a) above and
27-4, vessels designed for internal pressure shall be subjected to a hydrostatic test pressure which at every point in the vessel is at least equal to 1.3 times the maximum allowable working pressure to be marked on the vessel multiplied by the lowest ratio (for the materials of which the vessel is constructed) of the stress value S for the test temperature on the vessel to the stress value S for the design temperature (see UG-21). All loadings that may exist during this test shall be given consideration.

Please note the test pressure at any point shall be at least 1.3 x MAWP, for any horizontal or vertical testing method. That means it can be higher than 1.3 x MAWP, but not to the extent of overstressing the material, any near the yield limit.

Safer still, ask your Client to provide the test pressure calculations which you feel confortable with.
Cheers,
gr2vessels
Helpful Member!  roca (Mechanical)
24 Sep 07 21:45
Please let me know if my understanding is incorrect

Example Column
Column designed to ASME VIII Div 1.
Design pressure = 10 Barg (at top) at 100°C
Tan to tan length = 50m, Inside Diameter = 2m
Design static head = 10m with SG=1.0, this gives an additional pressure of 1barg at bottom
For cost savings and due to wind / seismic loads column is made up of various thicknesses.
As per UG-99, test pressure = 1.3 x MAWP (or design pressure if MAWP is not calculated) x Sambient / Sdesign.
As design temp = 100°C, Sambient / Sdesign = 1.0
Therefore minimum test pressure = 1.3 x 10 = 13 Barg

(1). IN SHOP – HORIZONTAL POSITION (NEW AND COLD)
Test pressure at top = 13 barg MINIMUM (see above)
Pressure at bottom = 13 + 2m static head of water = 13 + 0.2 = 13.2 barg
As column is made of various thicknesses all parts should be checked at 13.2 barg to ensure 90% yield limit is not exceeded. All nozzle reinforcements and flange ratings should also be checked.

(2). IN FIELD –VERTICAL POSITION (NEW AND COLD)
Test pressure at top = 13 barg MINIMUM (see above)
Test pressure at bottom tan line = 13 + 50m static head of water = 13 + 5 = 18 barg
All column parts should be checked at the applicable test pressure at the required elevation being checked to ensure 90% yield limit is not exceeded (e.g. add the applicable static head pressure at the applicable level to the minimum design pressure of 13 barg). All noxzzle reinforcements and flange ratings should also be checked.
NOTE: - wind / seismic loads should also be added and taken into account. Most clients reduce the wind load value to 50 or 75% of the design wind load during a hydor-test.

(3). IN FIELD –VERTICAL POSITION (CORRODED)
Same as 2 above except that corroded wall, nozzle thicknesses shall be used

If the above example had been for a BS5500 vessel then the test pressure for (3). would be lower as BS5500 has a (t / t-c)  factor in its test pressure formula (new thickness / corroded thickness).

Hope this helps
 
roca (Mechanical)
25 Sep 07 19:55
Carthago
I have checked and there isn't an Annex F in EN13445-Part 5?

I am looking at the contents listing for EN13445-5:2002(E), Issue 14 (2005-06)

Can you check and confirm

Thanks
BeardedBob (Mechanical)
27 Sep 07 8:46
roca,

The t/(t-c) term in PD 5500 increases the test pressure to allow for the presence of a corrosion allowance in a new vessel. "t" is the nominal thickness and "c" is the corrosion allowance. The scope of PD 5500 is new construction, although the note to 1.1.1 does allow you to use it to guide maintenance. I would recommend seeking specialist advice if you are dealing with significant corrosion loss.
roca (Mechanical)
27 Sep 07 19:53
Hi BerdedBob
My post should have read:
If the above example above had been for a BS5500 vessel then the test pressure for (3). would be lower than (2). as BS5500 has a (t / t-c)  factor in its test pressure formula (new thickness / corroded thickness).
carthago (Mechanical)
28 Sep 07 3:17
BS5500 does not exist anymore it is noew PD5500

Quite some differences with the old BS5500
for instance:

It allows the use of Nozzle compensation as per EN 1344xx

roca (Mechanical)
30 Sep 07 19:42
carthago
You didn't answer the question about the EN13445 Annex......???
Thanks

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