Crosslinked Polyethylene Vs. Fiberglass Reinforced Plastic Tanks
Aug. 25, 2025
Crosslinked Polyethylene Vs. Fiberglass Reinforced Plastic Tanks
FRP Tank - Eng-Tips
Hi All,
We do a number of engineering projects for API 650 and 620 metal tanks, and I'm reasonably well-versed in metal tanks. We've been approached to inspect and certify an existing fiberglass tank on an emergency basis (I understand the process is down until we complete our work). I have little experience with FRP materials.
The tank was originally designed and certified in by an FRP tank manufacturing company. I've read through API 12P, and it doesn't sound like there's much for testing requirements. Just a curing test (hopefully done perviously) and hydrotest. It's also low on design recommendations for bottom thickness and roof thickness. All I see is bottom joint detail and shell design equation based on 0.001E or 10% of ultimate strength. We have a piece of the tank and we plan to test to try to estimate mechanical properties (at temperature, see below). Bottom is flat on concrete, and roof is dome shaped). Radius on both top and bottom knuckles.
The tank was originally designed to contain sodium chloride (S.G. is over 1.0) with design temp under 100F. The client is now proposing water and temperature ranging from 176F to 212F.
Does anyone have experience with this sort of FRP tank project (specifically bottom and roof design), and can I get any feedback on mechanical properties of FRP at temperatures noted above?
Thank you in advance.
Hello pbc825, there are some common inspection practices for FRP tanks as we as parameters to think about when changing the tanks service conditions.
1) FRP is very good upto 100 F but after that you can begin to have problems if the tank is not supported correctly. The coefficient of expansion of FRP is roughly twice that of steel tanks and so when unsupported correctly, they may have buckling or other failures associated with this elevated temperatures ( usually occurs with high temp over a long period of time)
2) This expansion and contraction of the FRP may have problems located at the flange faces and piping connected to the tank. The tank will move and the piping is usually fixed in place.
3) try to find out the type of resins that were used in the original manufacturing? Are they Vinyl Ester resins? Polyester resins ? etc. this will help you find out the temperature rating for this type of FRP
4) Hardness of the FRP is critical as this will help you to determine if the FRP is softening or hardening with the service conditions. Use a Barcol Tester and ASTM D
5) Visual inspection - take a light and shine through the FRP tank and begin to look for "Crazing" - -cracks within the FRP tank. Determine i the cracks penetrate the resin coating by applying a penetrating dye and wiping off with acetone. If the acetone does not wipe the dye off the cracks, try to determine the depth of the cracks, lengths, how many in a 100 sq/ft area ( 10'x10)
6) Sounding for delamination and/or voids - take a large coin or a long slender want that has a metallic bead on the end of it, and tap the FRP listening to the sound. When you hear the sound change, focus in this area for potential delamination or voids. ( Again, use your flashlight next to the tank to "look through" the FRP.
7) Pressure test the tank - test using hydro statically with water or service medium. This should be done by a person trained in this testing.
8) "shininess" of the internal resin layer - when the resin is very shiny or dull, this can demonstrate that the FRP surface resins may need another coat(s) to the surface for longevity. The above tests also help in your decision to apply another coat of resin on the internal/external areas.
9) check the connection areas of both the roof and floors where they connect the shell. As the tank expands and contracts, this seam may begin to crack and needs repairing. if no the bottom, this is more serious than the top seam.
I hope this helps in answering some of your questions and if you have the final service product that will be entering into the tank, this also helps to see if the FRP will be able to handle the service.
I inspect 50-100 FRP tanks per year and so far I have not found one that resembles another out in the field. Try to write down a list of items of concern and this will begin to help you check off items that are not an issue with the new service or items that will become an issue.
Good luck and if you need anything else please feel free to write and I hope I can help out.
We do a number of engineering projects for API 650 and 620 metal tanks, and I'm reasonably well-versed in metal tanks. We've been approached to inspect and certify an existing fiberglass tank on an emergency basis (I understand the process is down until we complete our work). I have little experience with FRP materials.
The tank was originally designed and certified in by an FRP tank manufacturing company. I've read through API 12P, and it doesn't sound like there's much for testing requirements. Just a curing test (hopefully done perviously) and hydrotest. It's also low on design recommendations for bottom thickness and roof thickness. All I see is bottom joint detail and shell design equation based on 0.001E or 10% of ultimate strength. We have a piece of the tank and we plan to test to try to estimate mechanical properties (at temperature, see below). Bottom is flat on concrete, and roof is dome shaped). Radius on both top and bottom knuckles.
The tank was originally designed to contain sodium chloride (S.G. is over 1.0) with design temp under 100F. The client is now proposing water and temperature ranging from 176F to 212F.
Does anyone have experience with this sort of FRP tank project (specifically bottom and roof design), and can I get any feedback on mechanical properties of FRP at temperatures noted above?
Thank you in advance.
Hello pbc825, there are some common inspection practices for FRP tanks as we as parameters to think about when changing the tanks service conditions.
1) FRP is very good upto 100 F but after that you can begin to have problems if the tank is not supported correctly. The coefficient of expansion of FRP is roughly twice that of steel tanks and so when unsupported correctly, they may have buckling or other failures associated with this elevated temperatures ( usually occurs with high temp over a long period of time)
2) This expansion and contraction of the FRP may have problems located at the flange faces and piping connected to the tank. The tank will move and the piping is usually fixed in place.
3) try to find out the type of resins that were used in the original manufacturing? Are they Vinyl Ester resins? Polyester resins ? etc. this will help you find out the temperature rating for this type of FRP
4) Hardness of the FRP is critical as this will help you to determine if the FRP is softening or hardening with the service conditions. Use a Barcol Tester and ASTM D
5) Visual inspection - take a light and shine through the FRP tank and begin to look for "Crazing" - -cracks within the FRP tank. Determine i the cracks penetrate the resin coating by applying a penetrating dye and wiping off with acetone. If the acetone does not wipe the dye off the cracks, try to determine the depth of the cracks, lengths, how many in a 100 sq/ft area ( 10'x10)
6) Sounding for delamination and/or voids - take a large coin or a long slender want that has a metallic bead on the end of it, and tap the FRP listening to the sound. When you hear the sound change, focus in this area for potential delamination or voids. ( Again, use your flashlight next to the tank to "look through" the FRP.
7) Pressure test the tank - test using hydro statically with water or service medium. This should be done by a person trained in this testing.
8) "shininess" of the internal resin layer - when the resin is very shiny or dull, this can demonstrate that the FRP surface resins may need another coat(s) to the surface for longevity. The above tests also help in your decision to apply another coat of resin on the internal/external areas.
9) check the connection areas of both the roof and floors where they connect the shell. As the tank expands and contracts, this seam may begin to crack and needs repairing. if no the bottom, this is more serious than the top seam.
I hope this helps in answering some of your questions and if you have the final service product that will be entering into the tank, this also helps to see if the FRP will be able to handle the service.
I inspect 50-100 FRP tanks per year and so far I have not found one that resembles another out in the field. Try to write down a list of items of concern and this will begin to help you check off items that are not an issue with the new service or items that will become an issue.
Good luck and if you need anything else please feel free to write and I hope I can help out.
44
0
0
Comments
All Comments (0)