Hydrotest requirements of a jacketed vessel

[ChinaZh]

Dear all,

I also have questions regaridng a jacketed vessel.

Do UG 99(e)(2) and or UG (f) apply to a jacketed vessel, which it has full vacuum (15 psig design pressure) for interior shell design? The jacket covers the whole interior vessel except one end - the flat cover.

My customer advised that the interior shell will not be hydrotested due to full vacuum after I reminded them UG 99.

Thank you in advance.

 

[doct9960]

ChinaZh,

What exactly are the design conditions for the vessel and for the jacket? I can't figure it out from your question.

The entire paragraph of UG-99(e) applies to jacketed vessels. In my opinion, if you used the ASME Code to design and contruct your vessel & jacket (whether they are stamped or not), then you need to NDE and hydrotest your vessel/jacket per the ASME Code. Besides, how do you plan to check for leaks and flaws?

 

[ChinaZh]

doct9960,

The jacket design pressure is 232 psig.

My question is regarding hydrotest to the inner vessel, which will be in full vacuum.

So what about full vacuum vessel, is that non-code one?

Thanks.

 

[doct9960]

ChinaZh,

The inner vessel is within the scope of the Code. Refer to U-1(c)(2)(h)(2). Also see UG-19(a) and UG-21. The vessel and the jacket needs to be hydrotested separately. See UG-99(e) for more requirements.

 

[ChinaZh]

doct9960,

Interpretation of the code means this internal shell has the external pressure over 15psig, so can not be excepted from the code, right?

Thank you.

 

[doct9960]

ChinaZh,

Your vessel is NOT exempted from Code rules. It is not exempted because the differential pressure on the common element exceeded 15 psi (see U-1(c)(2)(h)(2)). The "common element" is the vessel part covered by the jacket. If the vessel will experience vacuum during normal operation, the differential pressure would be 247 psi (i.e. jacket internal absolute pressure minus vessel internal absolute pressure). For the vessel parts covered by the jacket, the external pressure design should be based on the differential pressure (not full vacuum) @ the most severe design temperature.

 

[ChinaZh]

Thank you

 

[ChinaZh]

Dear Doct9960,

Now my client agreed that the inner shell is covered by the code. But instead of follwing UG-99(e) to perform a hydrotest to the inner shell, they want to follow UG-99(f) since the another cover, which is not covered by the jacket, is designed for full vacuum and will not hold the hydrotest pressure.

Is this acceptable or is there any way to proof the inner shell instead of pressure testing?

Thank you very much!

 

[doct9960]

What are the MAWP's to be stamped on each pressure chamber? i.e. What is the inner shell MAWP? What is the jacket MAWP?

 

[ChinaZh]

MAWP marked on the drawing is 0 for inner shell and 232 psig on the jacket.

The client used FEA to verify that the inner shell is suitable for the differential pressure.

I read UG-19 & UG-99(e), I can't interpret the inner shell should only be hydrotested to 25.2 psig per full vacuum 15 psig.

Thank you very much.

 

[doct9960]

ChinaZh,

The hydrostatic test in the inner shell should be the larger test pressure obtained by the rules of UG-99(b) for internal pressure, or UG-99(f) for vacuum. Since there is no internal pressure in the inner shell, the rules of UG-99(f) applies. Thus, the minimum internal hydrostatic test in the inner shell would be "1.3 times the difference between normal atmospheric pressure and the minimum design internal absolute pressure."

If the condition in your vessel is full vacuum, the internal absolute pressure is 0 psi. For example, let's say the normal atmospheric pressure is 14.7 psi. The minimum internal hydrostatic pressure would be 1.3 x (14.7 - 0) = 19.11 psig.

 

[ChinaZh]

But this inner shell is subject to the external pressure caused by Jacket pressure.

So the inner shell should be designed to the differential pressure. Then the hydrotest shall be the 1.3 times of differential pressure?

UG-99(b) is for vessels designed for internal pressure?

Please help me to understand the code.

Thank you very much!

 

[doct9960]

Yes, your inner shell should be designed for the differential pressure, but it does not mean you need to do an internal hydrostatic test in the inner shell based on the differential pressure. The mechanical integrity of the inner shell against the differential pressure would be proven by the hydrostatic test in the jacket. Read UG-99(e)(1) over and over again.

There would be 3 hydrostatic tests on your jacketed vessel.
1. Hydrotest in the inner shell without pressure in the jacket.
2. Hydrotest in the jacket without pressure in the inner shell. In this case the inner shell should be dry and open for inspection.
3. Simultaneous hydrotest of the inner shell and the jacket. See the last paragraph of UG-99(e) about limiting the differential pressure between the chambers.

 

[ChinaZh]

Sorry, after read again, but...

Please help to understand "if the common elements of a combination unit...the hydrostatic test shall subject the common elecments to at least their design differential pressure, corrected...".

Does the "their design differential pressure" not mean 232 + 14.7 = 246.7 psig?

Really appreciate!

 

[doct9960]

ChinaZh,

"if the common elements of a combination unit...the hydrostatic test shall subject the common elecments to at least their design differential pressure, corrected..."

For your jacketed vessel, the above sentence applies to the jacket test pressure. But that does not end there. At the end of UG-99(e)(1), it says..."as well as meet the requirements of (b) or (c) above for each independent chamber." So the hydrostatic test in the jacket should be the larger test pressure obtained from the rules of UG-99(e)(1) or UG-99(b).

For your vessel, UG-99(b) applies for the jacket test pressure because you get a larger test pressure than the requirement of UG-99(e)(1). The jacket test pressure would be 1.3 x MAWP x stress ratio

 

[ChinaZh]

Sorry, doct9960 you have a slower student.

I thought "the common element" was the inner shell?

Thanks again.

 

[ChinaZh]

Doct9960,

Sorry, me again.

If the quoted sentence is for the jacket hydrotest pressure, why the code used "common elements" instead of "adjacent elements"?

Regards,

 

[doct9960]

ChinaZh,

Read UG-19(a). Common elements are the parts separating each independent pressure chamber. As I mentioned in my previous posts, the common element of your jacketed vessel is the vessel part (inner shell) COVERED by the jacket.

why the code used "common elements" instead of "adjacent elements"?

You will find the answer in a dictionary. From

http://www.dictionary.com/

common = Belonging equally to or shared equally by two or more
adjacent = Close to; lying near
If you use the phrase "adjacent element", this could mean any part covered by the jacket or near your jacket (even those parts not covered by the jacket) like the flat cover of your vessel.

By the way, UG-99(e) does not specify which is the jacket or which is the inner vessel. It only mentions "chambers". The classification on which chamber is the jacket or inner vessel will depend on the chambers' design conditions. All that I have discussed is based on YOUR particular jacketed vessel with inner vessel MAWP=0 & FV, and jacket MAWP=232 psig.

 

[unclesyd]

We have "fully" jacketed horizontal SS vessels ranging in size from 5'x16' to 6' x 21'. All have a 20" stuffing box, fully jacketed at one end and full diameter flanged head with a 20" stuffing box at the other. There three fully jacketed 12" flanged nozzles and with 1 fully jacketed 6" flanged nozzle. The inner shell is made from two stacked cylinders with about a 3" overlap (a dumpy figure 8).

These vessels operate 24/7/365

The approximate design conditions are:
Jacket FV and 90 psig @ 700F
Operating @ 10 psig @ 600F

Process Side 12" water at 700F.

Jacket fluid is vaporized Therminol.
Process fluid is polymer.

The jackets on the vessels have only been halogen or helium tested since day one (1943). The test pressure is normally 100 psi. The shell side has never been hydrotested. The design and testing has been reviewed many times and nothing has changed. The last one's were built in 1990's, by at the time one of the largest fabricators/designers in the business.

Even with numerous design changes the testing procedure has stayed the same.
Major changes.
The original design was with stay rods between inner shell and jacket, bad. This was changed to machined rings fillet welded to shell and plug welded to jacket. The stuffing boxes were a fabricated weldment then changed to a rolled ring machine to make them adjustable and to facilitate a full penetration weld to shell and jacket. All 17 vesels have had this alteration. The 6" nozzle was changed from a 4" and at the same time it was made a contour nozzle and it now tangent to the rear head of the shell.

Though not privileged to attend the meetings concerning the latest fabrications there was complete agreement by the insurance people and their AIs of all parties, the fabricators and our site design teams, along with our corporate design and safety.