HDPE Pressure Vessel 2

[mdcrose]

I am designing a pressure vessel composed entirely of polyethylene (HDPE). The main problem in designing this vessel is that the Sec VIII of ASME code seems to deal primarily with steel, when polymers are discussed they usually FRP.

Do I use the safety factors for steel vessels for my wall thickness calculations?

In section UG-34 there is an equation for a flat unstayed head, this equation has a “C” factor that is attributed to the joint used to attach the cap to the shell. Is this “C’” factor related to “E” (Joint Efficiency used in UG-27) of the cylindrical shell? If not how do I calculate the wall thickness of the shell with respect to the attachment of the cap?

TIA,
Michael

 

[prex]

You should at least consult ASME B31.3 that has a section on nonmetallic piping and pressure components. Your approach of transferring Div.1 criteria to nonmetals seems to me quite risky.
I've never calculated plastic vessels, but suppose that the bases for allowable stresses are not the same as for metals. B31.3 has also allowable stresses for PE. prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design

 

[gunnarhole]

There was an ASME report issued in 1989 called RTP-1 that discussed the design of reinforced thermoset plastic equipment. I don't know the current status of this document but it may give you a place to start.

Regards,

Gunnar

 

[mdcrose]

Thanks for all the help. I haven't had much experience with BPVC, I am a summer intern and just finished my third year of school with two more to go (5 year plan).

I looked into B31.3 but it still seems as though this type of code doesn't fit our product. Our design temp and press are 200 degrees C and 60 psi. The product is to be cylindrical, 2" dia. and 6" length. I am looking into injection molding both the shell and the end caps and then hot plate welding them together. Originally I had designated threads but the joint efficiency required the wall thickness to be quite large, thus making the OD greater than 2". Would you specify this as a pipe or a pressure vessel?

Sorry to be asking so many questions but my boss is on leave for a death in the family so I don't really know where to start.

Michael

 

[Kiranpatel]

200 deg C and HDPE do not seem to go together very well. I do not have my HDPE catalogs handy but from memory, you cannot use them in temperature above 60-75 deg C. Even then, you have start derating the material (above 20 deg C). Also creep efects become significant above this temperature.

All this is from memory from some time ago. So if I am talking rubbish, I apologise. I have not kept up-to-date with HDPE pipes.

Kiran

 

[mdcrose]

I was told that 200 degrees C was the design temp but that it will never experience temperatures above 85 degrees C from a clean in place treatment, standard temperatures will be in the 30 degrees C range. Sorry, I should have said all of this before.

Thanks,
Michael

 

[prex]

Well, 200 deg C was really nonsense, as noted by Kiranpatel.
You should clarify once for all the design data, as the answer will heavily depend on them.
Suggest that this object could be similar in size, thickness and fabrication methods to the gas buried pipelines normally used for distribution in urban areas.
Anyway we don't want to solve school problems on this site, so please go on with your own forces. prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design

 

[mdcrose]

Prex,

This is not a school problem. I am working on a new product that is undergoing revision and testing. Check out

http://www.liqui-cel.com/

There just seems to be a gray area in the code with respect to pressure vessels constructed of non-reinforced plastics. And the design data is not set in stone because the idea is still being fleshed out, hence the extremely large temperature value.

Michael

 

[jte]

Prex- Switch to decaf!

Michael- For a good primer take a look at the Harrington Plastics Engineering Handbook.

http://harringtonplastics.com/techpgs/handbook.htm

As others have stated, be careful with temperature.
Verify the liqui-cel.com address - it didn't work for me.

jt

 

[mdcrose]

Ok, Wow. I just made a big mistake. I was using Celcius and when I thought for a minute I realized how wrong that was, I read the value wrong. It is 180 degrees F. Please excuse my mistake.

Thanks so much,
Michael

http://www.liqui-cel.com

There were extra spaces in the last link.

 

[keeled]

ASME RTP-1 does not address solid thermoplastic design and construction. The only available information is contained in the DVS documents from Germany. the DVS 2205 standard is a good start. you can purchase the DVS/DIN standards from the following:

http://www2.beuth.de/index.php3?rub=10 Datenbanken&tar=/sixcms/list.php3?page=datenbanken

you will find that the temperature you have given will not be economical to build using solid HDPE - i would suggest a dual laminate (as described in mandatory appendix M-12 of the ASME RTP-1).

be very careful of the forming procedures, weld efficiencies, and welder qualifications. if you are not familiar with the design and construction of this type of equipment you should refer to those that are.

we, Viatec, inc.

http://www.viatec.com,

are a manufacturer of such equipment and are very familiar with the design requirements. we are also active in the ASME RTP-1, AWS, and ASME B31 committees for this type of equipment.

 

[Ag93]

Hello mdcrose,

This may have been made clear in the previous posts but the maximum recommended service temperature for HDPE pressure pipe is 140 F with a derating factor of 0.5.