Out of Roundness on Pressure Vessels After PWHT

[izamil]

I am sorry if this is long, but please bare with me.

We are currently facing a slight problem with one of the vessels that we have manufactured for a ýclient. The problem lurks in the results of heat treatment performed in a way where the vessel ýturned into an egg shaped object. ý

For your information, because the vessel is so long, we converted the vessel into a furnace. The ývessel size is the following: Inside diameter 4,877mm X 48,768mm tangent to tangent in length X ýý44 mm thickness. ý

The plates used are supplied by the mill with simulated PWHT.ý

The vessel was treated in the horizontal position with four units high velocity burners. Two on ýeach head end, and the other two from the top spaced equidistantly on the remainder of the ýshell with heat being diverted horizontally by means of a specially made 22 degrees diversion ýelbow. ý

We have placed 13 units outside saddle supports with none inside and started firing. Upon ýcompletion @ 50 degrees Celsius an hour for a total temperature of 610 degrees Celsius areas ýof the top third of the vessel fell to about 210mm from its own weight and nozzles. Maximum out ýof roundness per code is 48mm. ý

I kindly seek your expert opinion for a method statement and or a repair procedure to resolving ýthe current situation so as to bring this vessel back to code compliance requirements. ý

The code is the latest version and addenda of ASME section IIIV Division 1.ý

Our engineering manager stated the following:ý

The dimensional reports attached with NCR P01-1432/02 (Q11-D-204) for out of roundness of ýthe vessel after heat treatment indicates the following:ý

ý1.ý The heating in my opinion was not uniform at 4 burners as the result of this there may ýbe thermal pockets generated due to differential expansions at the burner’s locations. ý
ý2.ý This report does not indicate shifting of TRUE VESSEL center line of vessel towards 90° ýor 270°. The vessel might have bent like Banana or at some portion bent towards 90° ýand remaining portion bent towards 270°. If the vessel is bent towards one fixed degree ýthen turning the vessel by 90° say and doing heat treatment would reduce out of ýroundness. If the top half portion is bent and maximum deflection is at the center of ývessel length and towards one fixed degree than it indicates the introduction of internal ýspider supports. These spider supports shall be inter-connected so that it acts as a ýhomogeneous structure. This is one of the possibilities. Complete readings have to be ýtaken at 1 meter interval or at the shell course weld joints. ý
ý3.ý Jacking of shell would not help unless vessel is jacked beyond yield strength. To yield ýý44 mm thick shell, it requires a very big jack. Jacking of vessel would lead to jacked ýspots and it is not recommended by the writer. ý
ý4.ý Heating rate and cooling rate shall be faster as to avoid prolonged thermal stresses. ý
ý5.ý How this material behaves at 1100° F (HEAT TREATMENT) temperature is very difficult ýto assume. ý
ý6.ý Cutting the shell weld joint would be one of the disliked alternatives. ý
ý7.ý It is ad visible to take expert opinions particularly from metallurgical engineers pertaining ýto support etc before it is too late. ý
ý8.ý It is beyond my engineering capacity to deal with thermal expansion calculations, ýstiffeners outside or inside the vessel. ý
ý9.ý This problem may be new to us, but definitely not a new problem for thick vessel ýmanufacturers or thick vessel inspectors and they may give vital information about ýarrangement of internal stiffeners. We do not want to do it wrong this time. ý


I would appreciate any and all assistance you could provide, ý

 

[stanweld]

I am unclear as to the extent of the out of roundness. Is it throughout the length of the vessel or is it only at nozzle locations? If it is throughout, cut your losses now, scrap the vessel and salvage what you can. If it is only at specific nozzle locations, repairs may be effected using appropriate localized heat treatment and applied force.

Do not normalize!!!

 

[HeatTreater]

Just to let you know the e mail address for Cooperheat that was posted by UncleSyd. You can reach Cooperheat at

http://www.cooperheat-mqs.com

. They are a worldwide service company, and are well known in the Industry. Hopefully the address provided will get you in contact with one of their Representatives. Houston is the head office.
Hope this helps with your problem.

 

[quadswift]

I know I am not really helping, but you have received all the relevant responses / acvice.

I have never heard of doing PWHT in this manner. Why treat the whole vessel when it is just the welds that need doing?

And in future, do local electric PWHT.

Schedule is not always king, as you are finding out.

I do not want to appear too pessimistic but see also my comment on 'API visual inspection' thread in Inspection and Testing section of this web-site.

Who approved the procedures? (Did the client also approve them?)How does this manner of PWHT compare to the WPS/WPQR's in the PWHT condition?

I assume your metallurgist / welding engineer is now browsing through the situations vacant in the local papers.

Have you had the local ASME Inspector involved? Or are you ASME approved? And you will still have to get someone to stamp the name-plate.
Regards,
Quadswift

 

[unclesyd]

quadswift,
This type heat treating is done quite often by companies well versed in the art. I agree it sounds bad but the temperature can be controlled and the proper structural reinforcement supplied. The alternate routs present some problems also in heat treating sections as a unit then heat treating the closure welds.
It is ashamed that our advice came to late to prevent major repairs and additional heat treatment.

 

[Metalguy]

Just for info, we right now have to fix a large cylindrical pressure vessel (P3 steel). Dia. is ~18' and wall thickness is ~6". We have to make one end a little rounder-it's off by ~2", while the mating cyl. section to be welded to it is just about perfectly round.

Our method will be to use a 200 ton. hyd. jack on it, cold or at welding preheat temp. After making it round again, 8 "strongbacks" will be welded around the ID, and a big column/stiffener will be kept there until the butt weld is completed and PWHT is done-locally, via induction cables. I have little doubt that it will be successful.

 

[carljpme]

Why did you do an extended PWHT of 5 days? This vessel should not take more than 24-36 hours including ramp up time, holding and ramp down time. I am working in the middle east and I am guessing you had cooper heat to do the internal firing for the PWHT. First of all you have to distribute the weight of the vessel throughout the length of the vessel. I suggest building many temporary saddles with a wear plate that matches the OD of your vessel with a 150 degree minimum wrap. Make sure you have room on each side of each temporary saddle to account for thermal expansion. Do not go to Normalizing temperature. If you do you have to do mechanical tests for each material. This will be a nightmare and is a poor suggestion. You realize you still have to do a hydrotest and with a vessel of this size you had better be sure that your Zick calculations are correct. The amount of liquid weight and will be enormous for this vessel.