ASME VIII DIV 1 - UG80 Interpretation

[izamil]

I wonder if you could assist me with the code interpretation UG 80 relative to the out ýof roundness issue on vessels.ý

Overview:ý

I have built a horizontal pressure vessel with the following size:ý

Inside diameter 4,877mm X 48,768mm tangent to tangent in length X ýý44 mm thickness. ý
I wrapped this vessel to post weld heat treat it with four high velocity burners and applied ýtemperature @ 10.5 degrees Celsius an hour to the required temperature of 620C. everything ýwent fine until I started measuring the out of roundness where I am allowed 1% on shell ýcourses that do not have openings or 2% with those that have. ý

I am getting an out of roundness of up to 170mm. the vessel went like egg shaped. The upper ýpart of the vessel kind of sunk due to own weight of shell and nozzles on it. I have ýunfortunately not stiffened the vessel from the inside. I did the stiffening only on the outside. ý

Now, my question to you, how can you help me? ý

Could you please expand on ways and means of procedures on reading taking? How it ýshould be done? ý
ý
Is there anywhere in the code where concessions are made to either increasing the out of ýroundness tolerance or such? ý

Should I stiffen the vessel from the inside and re-eat it? ý

I would be grateful to receive the most intricate and well thought way out of this predicament I ýam in. ý

Are there any official or unofficial interpretations relating to the issue? ý

Thanks in advance for your kind assistance, ý

 

[bmoorthy]

The situation you have explained is rather unfortunate. I think the heating rate you mentioned is very slow.

The extent of Ovality you have mentioned is much beyond the acceptable limits.

Firstly if this is a U stamp job? Where is the job going to be installed (Which Country, what are the local regulations)

Secondly, You may consider rectification.

Check with Template, also measure ovality (If the job is in Horizontal position) Rotate the job and measure the dia in the same plane. That is if the first reading you took was in the horizontal plane , take the next reading also in the same plane, this would discount the self weight sagging effect.

You may also refer to BS5500(PD5500) refer the back side of the BS5500 for Questions and Answers, refer to question number 33. I have found the methods particularly useful.

On establishing which portion of the shell has gone out of shape you may consider rectification.

How to rectify?

I assume the ovality you mentioned is a local phenomenon, that is, it is not throughout the length. In which case you may consider cutting out the shell course and rectify and weld back the course.

If the ovality you mentioned is near the nozzle, then cut out a portion larger than the Nozzle opening and provide a fresh Insert plate made to the curvature, of higher thickness (To take care of the reinforcement requirements) and fit the nozzle to the insert plate, fit the insert plate to the shell and perform PWHT again.

Consider heating the job again and jack it with curvature moon plates. In this case you may have to check whether the properties of the material has not been affected by your rectifiaction method.

There are references in code where if the job has become Oval, then allow the designer to downgrade the allowable pressure, however, as i recollect, these provisions are used in glasslined vessels ( Refer to appendix).

These oval down grading is also refered in Froged vessels refer to UF. Unfortunately for welded shells these are not (atleast i donot know) applicable.

You may consider to perform Proof load test to convince your client that the job is still safe (Consider Strain gauging), but the procedure is cumbersome.

You may check with your designer whether he can redesign the job as Oval (Not a circular job, but as oval job) job and check whether the job is safe for use. You may consider employing FEM analysis for checking whether the job is safe to use even in the event the client uses the job under some pretext.

kindly keep us informed as to what transpired and what prevailed in the end.

Good Luck

 

[deanc]

How does the word "junk" sound? I would not accept nor buy this vessel. bmoorthy's repairs and backdoor approaches are creative,but you still have a vessel with a bad problem. I believe you are at the place where the more you work on it the worse it gets. Chalk it up to an expensive lesson and start over,get someone to help you with the PWHT.

 

[aclark]

I agree with deanc. You have a serious problem, and the more things you try to do to correct it it will only get worse. You may also have additional isses arise as a result of the attempted fix.

In addition, if the vessel is fixed there could be issues that arise when it is placed in service. My best advice ... start over..