CR4 - Thread_ MAP & MAWP in Hydrotest

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wijeeshAssociate

Join Date: Apr 2008Location: IndiaPosts: 27

MAP & MAWP in Hydrotest08/09/2012 4:55 AM

Dear Members

I have to do hydrotest as per UG-99B (1.3*MAWP).

But as per one of the project specification, hydrotest shall be performed as per the code, however MAP shall be used in lieu of MAWP.

What is the significance of this?

Also if i am having a higher thickness margin (given thk. - required thk.), the MAP will be higher. Also the hydrotest pressure.

The vessel is failing to hydritest pressure due to this. If increased the vessel thickness, the MAP will also increase again.

Kindly advise

Regards,

vGsh

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PWSlackGuru

Join Date: Jan 2007Location: In the bothy, 7chains down the line fromDodman's Lane levelcrossing, in the nationformerly known as GreatBritain. Kettle's on.Posts: 24660Good Answers: 638

Re: MAP & MAWP in Hydrotest08/09/2012 5:28 AM

"MAP" and "MAWP" are the same thing here. The test pressure is 1.3 times this value. What is the true problem - is it simply one ofinterpretation? What are the numbers involved?

Increasing the thickness of the vessel at this late stage sounds like "scrap it and start again".

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wijeeshAssociate



Dear PWSlack,Thank you for your reply.

Here iam having a corrosion allowance of 3mm. So the MAP & MAWP varies.My problem is, i have selected the hydrotest as per UG-99B(1.3*MAWP).Now i have incorporate the comment 'hydrotest shall beperformed as per code where MAP shall be used in leiu of MAWP"Here my hydrostatic pressure increases and vessel fails.Iam also tried with increasing the vessel thickness. But u know, the MAP increases wrt increase in thickness with hydrostatic pressuI presume that you understood the scenarioRegards,vGsh

__________________vgsh

PWSlackGuru


The design pressure is the MWP when the vessel is new.The MAWP relates to the corrosion of the vessel over time and its re-testing and certification at intervals under periodic re-twitnessed by the Engineer/Surveyor from the company providing burst indemnity insurance cover on the vessel. As corrosiocontinues with time, the MAWP will reduce with time. At some point, renewals and replacements of parts of or the entirety ovessel will become appropriate.The test pressure is 1.3 times either of the above depending on when the vessel is being tested and witnessed.

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Join Date: Jan 2007Location: In the bothy, 7chains down the line fromDodman's Lane levelcrossing, in the nationformerly known as GreatBritain. Kettle's on.Posts: 24660Good Answers: 638

It is far better for the vessel to fail its test with an incompressible fluid such as water than with process fluids while in use.failed test indicates repairs or replacement need to take place before process fluids are re-introduced to the vessel.

Is there anything here that is unclear?

__________________"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw,

Hajee

MohamedParticipant

Join Date: Apr 2012Posts: 1


Dear Mr.Wijeesh,

During the Hydrotest medium of water temp. is appx. 45Deg.C i.e ambient temp. and stress value of Vessels shell/Head material imore than that of max.design temp.,for example SA 516 Gr.70 plate material's stress value at 45Deg.C is 1406.46 kg/cm^2 and 1kg/cm^2 for 400 Deg.c. So vessel will not failure until having any weld joints leakage. Please check weld joint strength before stathe hydro test.

Still you get any problem please ask actual stress value of plate material and do the strength calculation reversely.

Hope you Clear.

Thanks

Hajee

CodemasterGuru

Join Date: Jul 2005Location: Stoke-on-Trent,UKPosts: 3377Good Answers: 98

Re: MAP & MAWP in Hydrotest08/09/2012 5:30 PM

Do you mean it has failed the hydrotest? In what way? Did a welded joint fail, or something else? If the thickness and hydrotest preshave been calculated correctly the metal stress on hydrotest would be well the UTS, so failure suggests very poor workmanship.

You're right that if you increase the thickness you also increase the calculated hydrotest pressure, so just as likely to fail the test.

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wijeeshAssociate



Dear All

Kindly ignore the previous discussion.

Sorry, the vessel is failing for hydrotest in design and not at the shop.

Please find below the details for better understanding.

Kindly consider design as per Div-2:

Vessel ID = 3006mm.

Material - SA 516 Gr. 70

Design Pressure - 7.9 MPa

Design Temperature - 82c

Shell thickness - 84mm

Corrosion Allowance = 0

MAWP - 8.791 MPa

MAP - 9.4866 MPa

Test Pressure = 1.43 * MAWP = 1.43*8.791 = 12.571 MPa

Stress at Hydrotest = 231.17 MPa

Allowable stress = 247 MPa (0.95*Yield)

Ratio = 0.935 (Pass).

Considering MAP in place of MAWP,

Test Pressure = 1.43*MAP = 13.565 MPa

Stress at hydrotest = 249.46 MPa

Ratio = 1.01 MPa (Fail)

Hope now its clear. The same scenario is happening for vessels in Div.1 also while considering MAP in place of MAWP in hydrotest.

Kindly advise.
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Regards

vGsh

__________________vgsh

CodemasterGuru



If corrosion allowance = 0, how can the MAP be higher than MAWP? If you calculate a slightly lower MAP you're OK. In calculatinghave you allowed for allowable stress at working temperature being lower than at test temperature?


wijeeshAssociate



Dear Codemaster

Allowable stresses are different at design temp (162@MAWP) and ambient (175@MAP).

Iam confused about the significance of using MAP in place of MAWP.

Regards

vGsh

__________________vgsh

CodemasterGuru



How is the MAP defined? I'm only aware of design pressure DP, MAWP and test pressure.

Whatever pressure you'r e going to multiply by 1.43 to get test pressure, you need to make sure thickness is such as to give strethat pressure less than 247/1.43 ~ 173 MPa. Then you're OK.


ANSONMember

Join Date: Jul 2012Posts: 9


Dear,

I think u r using some design sofware for calculation, dont get confuse.

lets solve it other way.

1. MAWP stand for maximum allowable working presure at corroded condition. the MAWP is obtained for the selected thickness of plless corrosion allowance, by using the same equation of UG-27. ASME div1. ( exp- selected thickness = 10mm, while required thic7.1mm). MAWP states that suppose after 10 yrs coorossion might has taken, the vessel can stand this pressure.

2. MAP stands for Maximum allowable pressure at new and cold condition, that is the MAP is calculate for selected thickness withoutcorroison when the vessel is new.( exp- selected thickness = 10mm, while required thickness= 7.1mm).

so MAP will be higher than MAWP is corrosion is considered. If no corrossion then both values are same.

3. FOR hydrotest 1.3*MAWP*(St/S). just select 1.3*DP*St/S. DP is design pressure, if u select MAWP instead of DP. u will be gettinthe results what u r facing now.

Read note 34 of UG 99B.

SALAAM!

ahmednabiParticipant

Join Date: Dec 2014Location: PakistanPosts: 4


A very informative discussion has been carried out above. I just want to straight out a few facts which even very experienced engineconfused.

1. MAWP is always taken in corroded condition (Ref: ASME BPVC Sec.VIII Div.1 UG-98) That means the MAWP is not effected oveyear due to corrosion( it should always be re-calculted after some repair work)

2. MAP is calculated at MDMT 'excluding' corrosion allowance like MAWP. This is very clearly mentioned in BPVC under General noteUCS 68. let me copy paste the exact wordings here just to avoid any confusion.

"The MAP is defined as the highest permissible pressure as determined by the design formulas for a component using the nominalthickness less corrosion allowance and the maximum allowable stress value from the Table 1A of Section II, Part D at the MDMT.

I hope this will clear the stuff up.

As far as the hydro-testing is concerned, MAP is always greater than MAWP so testing the vessel at MAP with temperature higher thaMDMT will always cause problems. this is the reason BPVC always uses MAWP for hydro-testing instead of MAP.

p.s: Correct me if I am wrong somewhere.

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