UG-99 (b) or (c)

[ElCidCampeador]

Code: ASME VIII Div.1
Case: Inox vessel 8"
From calculation, hydrotest pressure acc.to UG-99 (b)=6,5 bar; Hydrotest pressure acc.to UG-99 (c)=8 bar.
My client want to test at 10 bar (in the calculation there is a check if this pressure is ok).
Is this pressure acc. to UG-99 (b) or (c)?
Thanks

 

[XL83NL]

The key words in UG-99(b) is:

(b) Except as otherwise permitted in (a) above and
27-4, vessels designed for internal pressure shall be subjected
to a hydrostatic test pressure that at every point in
the vessel is at least equal to 1.3 times the maximum allowable ...

If the test pressure required by the client doesnt introduce any adverse effects, like (too gross local) yielding, I wouldnt be worried with a slightly higher test pressure.

 

[TGS4]

Regret to UG-99(d). Your answer is there.

 

[ElCidCampeador]

I've read them but I still don't understand. Is it UG-99(b) or (c)? Why?

 

[TGS4]

What don't you understand about UG-99(d)?

UG-99(d) doesn't say that it is (b) or (c), but can be between the two. What is the basis used for the UG-99(c) calculation?

 

[sharmass]

Dear ElCid
UG-99(c) hydrotest pressure is the calculated test pressure in new and cold condition of the vessel. It is derived based on the actual thickness used and in new condition (un-corroded) . Maximum allowable pressure (MAP) is reverse calculated for all pressure parts. This pressure is multiplied by 1.3 and the liquid head acting on that part is deducted to obtain the calculated test pressure for each part. Test position is important consideration. Minimum of this calculated pressure is considered as UG-99(c) test pressure. In any case this calculated pressure shall not be less than that in UG-99(b).

UG-99(d) states that UG-99(b)represent the minimum standard hydrostatic test pressure. UG-99(c) represent a special test based on calculations.
Any intermediate value of pressure may be used.

Exceeding UG-99(c) is not a good option unless support calculations are made to ensure that no pressure part is subjected to stresses close to yield stress of material.

 

[ElCidCampeador]

In my case 10 bar>UG-99(c), but I check with other calculation that the vessel could support this test condition. So what do I have to declare? Some people say (b), others (c)...I'm confused

Does it depend on the value itself or only by the way you calculate it?

 

[TGS4]

What is the basis used for the UG-99(c) calculation?

And what is the basis to supposedly justify the 10 bar value?

 

[ElCidCampeador]

10 bar is calculated using a new (fictitious) pressure design, whose ug-99(b) pressure test is 10 bar. Using these values, calculation is still ok, so I can apply to the vessel, but I don't understand if it's ug-99(b).

 

[TGS4]

This makes absolutely no sense. What do you mean by fictitious?

 

[ElCidCampeador]

I've run 2 calcs.
First one, with DP wanted by my client.
Second one, to check the new pressure test wanted by my client. This pressure test (10 bar) is not the result of the first calculation (10 bar is higher than ones acc. to UG-99(b) and (c) value from first calculation), so I've run another calculation where I suppose a new pressure design which has, acc. to UG-99(b), 10 bar as pressure test value (Obviously the pressure design of the second calculation is higher than the firt calc one's).
As data declared in my drawing result the DP of the first calculation, but 10 bar as test pressure (because second calculations are ok).

 

[TGS4]

What was the basis used for the original UG-99(c) calculation?

 

[ElCidCampeador]

What was the basis used for the original UG-99(c) calculation?

MAP - Hydro static Head, I suppose

 

[TGS4]

But what was the criteria, with respect the material strength, used to make this a calculated pressure?

 

[ElCidCampeador]

It's defined by client, there's no criteria.

 

[TomBarsh]

so, your test pressure is "Client Defined". It is not a UG-99(b) or UG-99(c) test.

UG-99(d) states that this Division does not specify an upper limit on the test pressure. However, the Inspector can reject the test in some cases if the vessel shows visible signs of distortion.

Further, although Division 1 does not specify allowable stresses for the test condition, some vessel owners may impose this restriction so it is wise to check the stresses for all components. This also will protect you, as the fabricator, who bears all liability for the vessel, from the vessel being overstressed and disqualified at test due to excessive deformation.

 

[sharmass]

ElCid,
One way to do is to reverse calculate the stresses (S) in pressure parts with pressure P = 10bar and thickness of the pressure part in new condition and ensure that the stresses are less than yield strength of material at room temperature.

You also need to talk to your AI about this pressure exceeding UG-99(c) and show him your calculations. You don't want to give him a reason to question it at the time of pressure test.

 

[ElCidCampeador]

My AI inspector says it's UG-99(c). Reason: it's calculated.

The MAWP from the first calculation is what will be declared in the nameplate. From the minimum thicknesses resulting of this calculation a second calculation is developed, where it's checked if these thicknesses could sustain the new condition of hydrostatic test acc. to client's request (10 bar). Of course, in this new calculation there's a new MAWP, but it refers to N&C condition, because it's used to check only client's hydrostatic pressure. In the real nameplate and in the data drawing it's reported only the original MAWP (from first calculation), with the new hydrostatic test value (from second one). Basing on these consideration, it should be UG-99(c).
What do you think?

 

[TomBarsh]

I don't think so.

UG-99(c) provides an explicit method to "calculate" the test pressure. Your client's arbitrary test pressure is not "calculated".

 

[ElCidCampeador]

UG-99(c) provides an explicit method to "calculate" the test pressure. Your client's arbitrary test pressure is not "calculated".

AI also says that any hydraulic test value different from UG-99(b) is by default UG-99(c).