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nur12 (Mechanical)
28 Jul 04 20:02
Hi,

In our project specification we've asked the Vendor to hydrotest vessel to 1.3 MAWP (new& cold). I've got a question from them - which hydrotest pressure shall be mentioned on the vessel nameplate, 1.3 x MAP new&cold or 1.3 MAWP (the pressure of the test done at the field)?

Their concern with noting the MAP N&C test pressure on the nameplate is that when they hydrostatic test in the field, they may refer to the nameplate and consider that this is correct and over stress the vessel. The only time that the 1.3 X MAP N&C pressure can be applied is when the vessel is in the shop.

On the other hand, 1.3 x MAP is the actual hydrotest pressure - shouldn't a vessel nameplate reflect the pressure a vessel actually was tested to?
What is your experience? I will appreciate your input.

Thanks.


metengr (Materials)
28 Jul 04 21:01
If the pressure vessel was designed and fabricated in accordance with the rules of ASME Section VIII, Div 1, the nameplate of the vessel must be stamped in accordance with UG-118, specifically Figure UG-118 (page 91 of the 2001 Edition of Section VIII, Div 1 , 2003 Addendum).

The nameplate requires the MAWP and design temperature. A standard hydrotest is done at 1.3X MAWP with a minimum of 70 deg F water (field or shop). A calculated hydrotest pressure can be used in accordance with UG-99 2c. However, the MAWP is still stamped on the vessel nameplate. I have not seen MAP N&C used on nameplates for ASME Section VIII, Div 1 vessels.

In some cases the design pressure can be used as MAWP, but you need to stamp the nameplate per Figure UG-118.

The only scenario I could think of where the nameplate would be stamped differently is when a vessel will be installed in a Jurisdiction or country that requires MAP N&C to be stamped in lieu of MAWP.
GenB (Mechanical)
29 Jul 04 2:17
MAP N&C can be included in the name plate but outside of the boundaries of NB and ASME data: on top or below the Code stamping and is used for reference, cautionary statements or merely as additional data only.
ER
deanc (Specifier/Regulator)
29 Jul 04 9:04
There are a number of Codes (not ASME) that allow you to build to ASME but require you to record the test pressure on the  main nameplate or another.

70deg. is not a required test temp. for SecVIII-Please see UG-99(h)but keep in mind the requirements of the NBIC for later testing. Also review UG-99(c)(d).

To determine test pressures review Appendix 3 and UG-99(b).

InnSk-I would not worry about a later test,the one doing the testing should consider the results. See ASME SecVIII UG-99(d) and NBIC RC-2051 and RC-3031.
codeeng (Petroleum)
29 Jul 04 11:37
These is no Code requirement to put the test pressure on the nameplate. If you choose to put it on then I would put both the shop test pressure (1.3 x MAP) and the routine field test pressure (1.3 x MAWP).
metengr (Materials)
29 Jul 04 12:02
In reviewing these posts, my only concern would be too much information stamped on a vessel. The hydrotest is performed by code to assure no gross material defects and that the  vessel, by design, doesn't fail. The standard hydrotest is typically a one time event to meet this requirement. Why would one care about stamping this information UNLESS it is either required by other codes or by the Jurisdiction? If you have concerns about exceeding the MAWP new or cold, they are unfounded because the multiplier used for the hydrotest (1.3) takes into account not exceeding the yield strength of the vessel material. I believe the Code does not place an upper limit to hydrotest pressure - minimum 1.3X. The only concern is to make sure you do not result in plastic deformation after a hydrotest.

Subsequent tests on the pressure vessel are normally pressure tests, and as deanc rightfully pointed out, follow NBIC rules (if applicable). I really see no reason to stamp hydrotest pressure when it is known that a hydrotest is conducted above MAWP.
Helpful Member!  jte (Mechanical)
30 Jul 04 18:28
I generally agree with the postings above. I see no advantage to including the hydrotest pressure on a nameplate. The hydrotest pressure will vary based on several issues: Original or repair hydro, shop (with vessel horizontal), shop (with vessel vertical), or field.

With a tall vessel, the shop would most likely test in the horizontal. A subsequent field hydro with the vessel in the vertical position can cause the bottom head to see a pressure to which it has not been previously exposed nor designed for.

Another consideration for field hydrotesting is whether the foundation can support the weight of a large, normally vapor filled, vessel full of water. Often, the foundation cannot support that load.

Adding a hydrotest pressure to the nameplate adds no value and may encourage a test which will cause failure of the vessel or foundation.

jt
unclesyd (Materials)
30 Jul 04 21:45
jte,
I have never seen a vessel designed that couldn't be filled with water in the operating position. It is a given that operations will manage to fill it to the brim.  Most of the concern is of over stressing comes in the inadequately support tall vessel in the horizontal position.  
Most PV programs will give you the weight empty, operating based on the input data and the weight full of water.  All our foundations are designed to carry the heaviest weight of the vessel.  
jte (Mechanical)
2 Aug 04 12:42
unclesyd-

I'm sorry you haven't seen a vessel which couldn't be filled with water in the vertical position! What that tells me is that you haven't been involved with tall relatively low pressure vessels. Say an atmospheric column 150' T-T x 20' diameter at say 25 psi and 700°F. The head from a full water load would be 65 psi. So this vessel designed for perhaps 20' of liquid on the bottom would see roughly 100 psi on the bottom shell course and head during a vertical hydrotest. Nearly four times the design pressure...

I'm happy that your foundations are designed for a full water load. In my past life at a major E&C firm I ran into situations where the foundations were not adequately designed for a field hydro. I witnessed one hydro of a particularly tall (well over 200') field fab vessel where the structural engineer had surveyors out during the hydro to verify that the foundation wasn't beginning to tilt. That is not a great indication of confidence in the foundation...

jt
unclesyd (Materials)
2 Aug 04 21:12
Seen plenty of 100' + plus several 220' T-T x 24' base.  I saw a 110' NO absorber fall while erecting never got to check the foundation.  It wasn't ours, but they were using our foundation design.
It was corporate policy never to push a foundation or anchor system on any vessel.  A little steel, a few more yard of concrete, and a competent designer goes a long way in the engineering  of supports.  As I stated before all our vessels no matter how large are designed for sustained 140 mph winds from any direction, that in itself goes a long way to carrying the weight full of water.  We have tested them all under these conditions.  

We did pay a little extra in material for FV/15 psig columns for this capability but like every other company we could rely on operations to flood anything we could put out there and they obliged us.  

Even on  our structured packing columns we still use a 100% flood design.  This is good way to start a column up, 80% flooded with 100% reflux.  On some 90' internal condenser columns with tunnel trays with a 125,000 pph circulation we can flood it in a second or two.  

Just for curiosity what would be a level of flood, liquid load, to design a column for use with valve trays?
IvanKFC (Mechanical)
20 Aug 04 21:06
The calculation have to take in account hydro in vertical and horizontal position checking the stress on test pressure condition . In the name plate you have to put the test pressure and position of the test. For a tall column you have to put MAP ( shop) & position and MAWP ( field ) & position . I am envolved in a modification of an existing tall column where the original - foundation and mechanical - design did not take in account field hydro test pressure .   I did not see in UG requests definitions requests for field hydro test pressure .
CHD01 (Mechanical)
20 Aug 04 23:02
No disagreements really, but I have one question.  When rerating or re certifying an ASME vessel for service following repair or redeployment years after original manufacture , the issue of what hydrotest pressure was used is of enough importance that I would have thought the preference would be to include the hydrotest pressure on the nameplate; particularly since whether 1.3 or 1.5 was used will not be readily determined even with the date of manufacture known (use of 1.3 factor is a recent revision to code).  This ratio is a factor of year built, material of construction and design conditions.  This I view as good insurance against up to date drawings being available.

Comments.

The more you learn, the less you are certain of.

metengr (Materials)
21 Aug 04 13:30
The issue of rerating an existing pressure vessel falls under the requirements of the National Board Inspection Code (NBIC), if the vessel was originally registered with the National Board and second, if the Jurisdiction adopted the NBIC.

As part of the rules for altering a pressure vessel, the NBIC requires a Form R-2 that has to be filled out and signed by the Inspector. On that form, is the hydrotest pressure that the item was tested to for the alteration. There is no reason to stamp this information on the vessel. If the nameplate was stamped with an R symbol indicating an alteration, the hydrotest information will be on Form R-2.
JoeTank (Structural)
21 Aug 04 16:08
I know a few of you would like to have the test pressure on the nameplate, but that could be very dangerous when pressure vessel rookies are involved.  Just because a vessel was pressure tested when it was new in no way implies that it's safe for that pressure again sometime in the future.  Any future test pressure must be verified as safe after taking into consideration the vessels present condition.  In-service corrosion or previous alterations may reduce the permissible test pressure.

Steve Braune
Tank Industry Consultants
www.tankindustry.com

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