Local Loads on Heads , help with Possible WRC Application 2

[VPbris]

Hi,

I need some guidance on assessing some local loads on a torispheric head.

It is a vessel for cryogenic Argon storage, for those who are not familiarized with it, it consists of an stainless steel vessel inside of a carbon steel vessel. The space between the vessels is filled with a powder named perlite which is a good thermal insulator. Also, vacuum is applied on this anular space to improve thermal insulation, as the temperature inside of the stainless steel is at around -190C.

Right now, I'm concerned on assessing the local loads caused by the internal vessel on the external vessel. These loads are due to the weight of the internal vessel and the way it is supported, as you can see on the attached Figure circled in red. Also it is worth to mention that the centroid of these support beams are located on the same centroid of the tubes that support the external vessel, so the load is probably transfered efficiently.

On the top head of the internal vessel there are three links that are connected to the top head of the external shell, but these links are only for balance purposes and do not carry any considerable loads when the vessel is operating.

So I ask, how do I assess these local loads on the external head of the vessel? (Remember that it is also submited to external pressure (vacuum))

I'm not familiar with the WRC procedures. However, before posting this did a quick search and saw that this maybe could be a case where the WRC 537 should be applicable. But before diving into it, I'd like to hear your comments on the matter.

Kind Regards

VPbris

 

[TGS4]

In this situation, with vacuum conditions, you are somewhat less interested in the stresses (as would be appropriate for the failure modes of Plastic Collapse and Ratcheting) and more interested in the failure mode of Collapse From Buckling. In that sense, you will need to do something much further beyond what is contained in WRC 537/297.

 

[jtseng123]

VPbris,
I can not open the attachment. However from your description, that is so called vacuum insulated dual wall storage bullet, with perlite filled in the vacuum annular space that I have purchased in the past. Internal vessel will be well supported and guided by structure in the annular space, also allowing for thermal movement. The pipes between inner and outer vessel will be routed around in the annual space to minimize thermal stress. Only a few suppliers in the world can design and fabricate it. They will use FEA to analyze.

 

[VPbris]

Hi,

Thank you for your replies.

@TGS4
I agree with you. When you say I'd have to do something much further, could you please point me into the right direction? Any inputs or references would be greatly appreciated. (PS: As I said I`m not familiar with the WRC procedures, are they applicable only for Plastic Collapse and Ratcheting failure modes?)

@jtseng123
That's exactly it. Completely agree with you when you say few suppliers can design and fabricate it. However, there are a lot of suppliers who can`t design it and still fabricate it, mainly on the south side of the hemisphere. I know it is a very complicated design, but I`m trying to figure it out bits by bits. Hope someday I'll get it fully.

Kind Regards,
VPbris

 

[TGS4]

As jtseng123 very helpfully pointed out, the highly skilled and knowledgeable fabricators of this type of equipment use FEA to analyze it. If they are fabricating it to one of the ASME Codes, then that analysis will be done in accordance with ASME Section VIII, Division 2, Part 5.

You would be best advised to engage the assistance of an expert in these matters. We're talking about at least 5 years of intensive mentorship/on-to-job-training to get you to a place where you could be doing this on your own.

 

[MrPDes]

The fabricators do not have highly skilled engineers.

I regularly deal with six fabricators across Europe, producing cryogenic storage tanks from 10m³ to 1200m³ in size.

The only reason five out of six use FEM is because they don't have the engineering skill to design using hand calculations. They try to dazzle the customer with colourful pictures, but when you look closer, they make the most simple critical errors. The fabricators are very reliant on the purchasers engineering team to teach them how to design each vessel.

My company designs using hand calculations and then goes through the immense cost of reviewing and correcting incompetent fabricator FEM designs. Only one fabricator in europe is capable of designing using hand calculations. I'm sure it is the same all around the world. The fabricators simply scale something they have fabricated before and then dazzle you with pretty FEM and then hope for the best.

I wouldn't be surprised if there are thousands of tanks in service today which have broken internal support structures and therefore the internal vessel is resting on top of the perlite powder.

 

[VPbris]

Hi guys, sorry for the late reply,

@TGS4
I really appreciate your advice. Unfortunately I do not have access to these professionals and mentoring at the moment, so I have to go the harder way. I'm studying more about FEA on vessels and getting more familiar with div 2. Hopefully someday I can do it by my own.

@MrPDes
I agree 100% with you, I even managed to get the calculations to look at from a a big company in South America, and I almost couldn't believe it. They only use the UG-28 to determine minimum thickness and go by it. Some other suppliers do not even calculate the repads on openings.Also, they do exactly as you said, they just scale things. From your expertise, could you give some advice on the the aspects I should look more carefully or indicate some references? I would be very grateful.

Regards