PRESSURE VESSEL REPAIR 1

[beercia]

What is the correct procedure to carry out a repair of a semi spherical head on a LPG bullet that was damaged by transport. The head was deformed and buckled towards the inside. Can it be straightened out and can it be repaired using a patch of the same material on top of the damaged area?

 

[jte]

beercia-

"Cut to fit, paint to match!"

Cut out the damaged section and butt weld in a formed patch. Make sure you are using SA grade material of the same type as the head and that the weld procedure is ASME qualified. Don't forget the PWHT if necessary to maintain ductility for an autorefrigeration contingency. Depending on where you're at, you may be required to have an Authorized Inspector involved. At the very least, make sure you are using a crew which is pressure vessel certified/qualified/experienced.

Hammering out the damaged section and covering it up with a fillet welded lap patch are not good solutions. Depending on where you are, that may be considered not only poor engineering but illegal.

jt

 

[WBH]

jte is correct installation of flush type patch is correct repair method.

Inorder to maintatin the joint effeicney of this head as per degsing calculations (assuming original je=1.0) a full radiographic exmaination of the repair weld must be performed.

wbh

 

[jsummerfield]

Assure that the vessel design temperature is not below -20 degree F. Low temperature design temperature changes the rules.

 

[deanc]

jte has outlined the correct path. See current NBIC.

 

[MJCronin]

beercia,

I suggest that you strongly consider filling for monentary damages from the shipper and getting a new "bullet"

LPG/propane horizontal tanks are commonly called "bullet" tanks and are typically equpped with "hemispherical" heads. The contour of the construction makes this type of head difficult to repair. Furthermore the high strength materials typically used (I seem to remember ASTM A622???) cause repair problems

The MAWP for propane is 250 psig....nothing to fool around with.

This type of tank is so common and produced by so many vendors,it may be worthwhile to just replace it. At least compare the cost of a competent "R" stamped repair with replacement.

Or...... perhaps, do you work for some tyranical butthole MBA that is forcing you to repair of this dog.....

My opinion only

MJC

 

[bmoorthy]

This is if you do not want a patch work and want the job to look like a modification instead of rectification and If you want to avoid Radiography. Instead of a patch provide a dummy Nozzle. That is cut out the deformed portion, Weld a Nozzle pipe (Size it accordingly) and provide blind flange. Perform Hydro test.

Second option:Check with your local authorities regarding the possible use of FEM to check whether the job is safe as it is (Leave it as it is)

Third Option: Provide Heating coil from out side (In the deformed location) and jack it from Inside to the required shape and subsequently perform SR. Here simulation test or PTC is not required, subesquently perform (Optional) UT and MPI and perform Hydro test.

Option 4: In one of the past case (De oxy tower) we had our shell deformed due to transportation, after extensive discussions with client and their consultants we provided pad covering the deformed area. ( This was not a U stamp job, Code was used as only as a design standard the job is not in US). Here we used FEM to check whether the deformed locations could be left as it is and found it safe. It is now 7 years every thing is fine till date. Yearly inspections results are satisfactory.


(Assuminig the job is Carbon steel).

 

[deanc]

bmoorthy-Option 4-WOW! We refer to this as a "scab" or "bandaid" patch. There are many very good reasons not to do this and that is why it is not permitted in most areas of the US and Europe. It fixes nothing.

Not to rude,but I am glad I am nowhere around this one!

The rest of your ideas may be "doable".

 

[ExAI]

I'm with MJC on this one...quit fooling around with half hearted repairs...this is LPG, someone could get hurt. Recommend a replacement head as a minimum, but more likely a replacement vessel (cost factors).

Lane Baker
Baker Quality Services
LaneBQS@att.net