Modifying a pressure vessel

[ed72073]

Hi everyone,

I am a newbie to this forum, but I have some question regarding modifying a double chamber pressure vessel. These vessels are purchased and certified from the manufacturer and then are modified. I feel that a vessel can be modified only if it is done by a certified person and or then have it certified again.

1) Can a vessel be welded on? When I mean welded on is a 36" diameter ring welded to the top of the vessel so a storage container be bolted on top of?

2) Can a hole be drilled in the vessel to weld in a coupling?

3) If the original certification tag is remove and then the vessel is shipped to a customer is the vessel certified?

My feeling is that any tank that is modified in anyway needs to be certified again. otherwise there is the potential to have an explosion and people work close to these vessels everyday. I will post a photo later to show exactly what I am taking about when I have a chance.

 

[desertfox]

Hi ed72073

Your right to be concerned any modification might break the rules the vessel was designed and manufactured to.
Do you know what code the vessel was made to? thats your first port of call.
Any welds done on the vessel after manuacturer might need to be done by a coded welder, not just any welder.
Check the modifications being done against the vessel code it was made to and see if the modifications are allowed.

desertfox

 

[racookpe1978]

Very true - But, the original poster said that this (very large!) 36 inch ring was welded on to the top of the pressure vessel "so a storage container" can be attached.

He (his company) is now also accountable for the added weight of the container and its contents, added moment, added wind load, added shear stress, and added bending stress onto the upper head of the original pressure vessel caused by the storage container, the welding itself, the shock/impact of pouring material into the storage container under operations, and the "ring" stress of a load onto the vessel.

I think "welding" is the least of his problems - if his boss thinks that welding into a pressure vessel isn't important enough either.

 

[JStephen]

Some areas don't regulate vessels, and there are some exemptions in the ASME code for certain classes of vessels that are not required to be built to the code. So if you take a coded vessel, perform non-code regulations, and sell it as a non-coded vessel, that may be perfectly okay as far as the legalities and/or the code go. It would depend on the circumstances, location, and code being used.

 

[ed72073]

These tanks are usually 36" diameter and 6'-7' tall (without the legs) and are used for shot blasting equipment. The reason for a double chamber is to have one part always pressurized and the other to do an exchange. The storage area does not add much weight, the media being used adds about 6k to 8k itself.

The tanks are used in many UAW automotive plants here in the states as well as Mexico, Canada, and China. The persons that have performed the modification are not certified welders. The area is simply cleaned off and a single noncontinuous weld with a mig welder. The company reason fro modifying the vessels is because they can have them faster for the projects. The real reason is because the owner can not read a blueprint or thinks the manufacture can not make these modification to his request. To be honest there are up to 150 - 200 vessels out in the field with these issue. Someday someone will get seriously hurt.

I am trying to figure out how to attach a photo as well as a drawing to give more insight.

 

[ed72073]

I think I have figured how to attach a photo, see if this works.

 

[metengr]

Excellent example of why modification to pressurized vessels is not something to be taken lightly. If you want good guidance review either API 510 or the National Board Inspection Code (NBIC). If you follow either document you will know what is required in terms of engineering, Quality Control and documentation.

 

[ed72073]

One other thing I forgot to mention. The company also has welded blocks onto the vessels to mount a pneumatic vibrator that run constant when they are pressurized.

 

[jtseng123]

Perform proper NDE and do hydrotest, then it shall be fine.