Risk between Welded and Seamless Vessel

[leel]

It is know that seamless vessel will be always the best, but base on engineering calculation both is safe within the design thickness. However, base on safety point, there ma have some different. Thus, can anyone help to give me some safety factor between this two types of vessel.

 

[metengr]

leel;
No, I don't agree with your statement that a seamless vessel is always the best. Why? Improved safety - no. Improved reliability- no. Lower Cost- no.

For example using design by rules in ASME B&PV Code, welded design with good engineering practices will result in an equally safe and reliable pressure retaining item that could be manufactured at less cost. Looking at other international boiler codes I would expect the same conclusion would be arrived as I mentioned above.

Code committees are deliberate in assigning necessary strength reduction factors for use in welded fabrication. I am not going to get into detail because you should review the Code yourself to understand what is required for welded fabrication.

 

[MJCronin]

I have never encountered a "seamless vessel". What exactly does this mean ??

I am aware and have specified "seamless" pipe..(seamless only refers to an axial welded seam).......but in the case of piping beyond a certain diameter, seamless is not available.

Any explanation of terms ??

 

[jte]

MJC-

Not unusual to have high pressure, reasonably large diameter reactors with shell cans which are forgings rather than rolled plate. See the schematic near the bottom in

http://memagazine.asme.org/Articles/2009/May/Pressure_Builds.cfm

for one example.

jt

 

[MikeMet]

jte is right, the majority of vessels made to ASME Section VIII, Div 3 are forgings with no welding with different styles of end closures, such as breach lock. They do it specifically to get away from welding. It is generally accepted that any welded vessel in put into service with some type of discontinuity, just not all discontinuities rise to the point of begin defects. There can also be discontinuities in forged vessel shells, but they are typically not many and may not be as detrimental.

MJ is also right in that welded vessels can be just as safe as seamless. I hear the seamless vs. welded issue in piping and tubing all the time. A welded pipe or tube can be just as reliable and safe as seamless given it is properly fabricated and tested. The same holds true for vessels made to any recognized fabrication code.

 

[rmw]

I have experience with high pressure vessels (heat exchangers) that had forged tubesheet and channel lips and forged channel heads and forged nozzles all of which were several inches thick. How were they all attached to each other? Welded.

rmw

 

[leel]

Hi Metengr,

As I mentioned before, welded vessel can be safe as seamless if following the code. Again, it can be also some reasons that make it unsafe in the long run, for example, corrossion on the weld join, since welding may spoilt the material structure. Besides, there is also possibility for the weld join (since the weakness join) to crack due to environment impact.

Thanks
Lee

 

[gr2vessels]

Sorry to disappoint Lee, but if you use welded pipe or seamless pipe it makes no difference for the design of a pressure vessel (unless prohibited for process reasons). The only thing that makes difference is your weld, joining the shell with other components. Then you might spoil the good material structure of the welded or seamless pipe you bought to fabricate the vessel. And I hate to break this to you, but the environment is only impacting on a bad vessel design, not on properly welded joints (refer to ASME VIII, IX, etc...).
cheers,
gr2vessels