Body Flanges on Columns 5

[Narbij]

Hi Community,

We're looking at installing a tall, skinny trayed column - 36" ID X 140' lg. (including skirt.) DP@DT: 65 psi @ 350 deg F. Sour service. ASME Section VIII-1 is the design code

There are logistics issues with moving something that long as one piece so body flanges have been proposed to avoid welding. I prefer welded construction since there is the obvious(?) perception on potential for leak (not sure how real this is.)

Anyone have any experience with body flanges on columns?
Is the perception of leaks a reality? If so, can it be designed for or prevented through regular maintenance?
Are there any long-term drawbacks to watch out for?

Thanks, in advance, for your thoughts, opinions and experience.

 

[Christine74]

I haven't seen a body flange installed in a column before. Trayed columns that are too long to ship in one piece are normally just welded together on site. Leakage is always a concern with flanged connections, even when following best practices for tensioning the bolts. And any leak in a Sour service could be a huge problem.

I also don't think it's practical to have a gasketed joint in the middle of a trayed column. In order to replace the gasket you'd have to bring in a crane and lift off the top half of the column, and the lifting operation could displace some of the trays so you'd need to inspect them again.


-Christine

 

[SnTMan]

I don't have experience w/ columns, but this one seems long and skinny to me. I'd avoid bolted joints if I could.

EDIT: I might have better said bolted gasketed joints. There are weld ring gaskets...

Regards.

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Narbij]

Thank you Cristine74 and SnTman, for your thoughts.

@Christine74: appreciate you confirming the fear is real.

@SnTMan: you seem to have provided your thoughts based on the shape (i.e., long and skinny.) What about that shape drives the caution against bolted joints?

Thanks.

 

[SnTMan]

Again, no experience but it seems it would be more likely to flex under lateral loads (i.e. wind) said flex being imposed on the gasketed joint. Undesirable

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Cobra17]

You probably don't have to worry about gasket seating for the lower connections

 

[SnTMan]

Likely not

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[r6155]

This long vertical PV is not a problem in one piece (no body flange). It is normal to add a structure to the middle height to resist winds or earthquakes.

Regards.

 

[FMJalink]

Hi Narbij,
Use of body flanges is quite common in some types of industry for small diameter columns. For limited temperatures, limited pressures and limited corrosive attack I would not worry too much to use body flanges. Most of those I met were designed for, or modified to use, structured process packing. With vacuum service the inleak or air should be allowed and taken care of. When the medium is very corrosive to the selected body flange material, I would not use body flanges.

Personally I prefer such types of columns to be in a structure, where it is supported from at somewhat below the middle and guided on a high elevation. The access to the column and instrumentation can than be from the structure. If on a skirt, you will have to add platforms and cage ladders, which will be quite a challenge with small diameter columns concerning design and use.

If the reason to use body flanges is placing the column only, I would not go for body flanges, unless there is no access for a larger crane.

There are many things to consider with the use òf body flanges in a column. There should be good reasons, the surrounding should be designed for them and inside of the column should be such that it allows or requires body flanges.

 

[Narbij]

@FMJalink: Thanks for the thoughtful response. Indeed, these flanges are being proposed purely for ease of installation - to me, this not a good reason when welded is practical (I.e., ship in 2 pieces, weld on site and erect OR erect and weld in-situ.) There is indeed risk of corrosive attack at the flanges.

Unfortunately, we're in a pretty congested footprint so a structure, although desirable, is out of the question

Thanks again for confirming I'm pushing the right choice.

Thank you to everyone that weighed in for your thoughts, knowledge and experience. Very helpful.

 

[r6155]

This column is lightweight and not too tall.
Avoid welding and RT (100% ?)in situ. Avoid the hydrostatic test (horizontal) in situ.

Regards

 

[shvet]

I had been working with several flanged vacuum columns 20-25m height for 9 years and we saw consequences almost every day. Flanges are flexible even they seem rigid, gaskets are not resilient even those were specified to be so, bolts/studs release its torque. Be ready to face with unavoidable leakages. The only way to get closer to some flange tightness level is to provide extra supports on column shell to decrease stress. An expensive option I should say.

Anyway after all possible means will be implemented I do not believe that after ~10 years in operation personnel would prefer flange. Even 70' is too much to be compensated, 140' has no a chance.

Be noted that large metal structures/equipment are rigid on pictures/drawings. In reality when you climbed on top of one you figure out the opposite.

 

[Narbij]

@shvet: Thank you for sharing your experiences. I make it a point to climb the tallest structure I can safely at any facility I have worked at to get photos - indeed, I have learnt, first hand, that metal structures look far more rigid on paper than reality. This comment pretty much settles it for me - no body flanges on this thing. I will stand my ground and we will make it work.