AWWA D100 Tank Corrosion Allowance

[Rabbit12]

Looking for some input on typical corrosion allowances for D100 welded steel water tanks. Working on a spec and I want to be reasonable compared to an industry standard. The D100 standard doesn't provide any specifics that I can find. Any experience on this forum?

 

[zurch1818]

I don't have D100 in front of me...but going from my memory, that seems right that there isn't any specific guidance. Maybe there is something in the commentary? I can look tomorrow when I get in the office.

I've analyzed what seems like 100's of tanks for wireless carriers and 95% of the time the tanks are at a DCR of 99% in the original condition (before any telecom loads put on top)...especially the tanks from the 50s/60s. I usually think I messed the calcs up if I don't calculate this DCR.

My guess is they get around accounting for any corrosion issues by specifying regular maintenance. They also have a pretty low allowable stresses. For example, A36 has an allowable stress of only 18ksi. They do still allow the 1/3rd increase on flexure...even in the newest standard that came out in 21.

 

[JStephen]

Something like 80% of AWWA tanks do not have any specified corrosion allowance. Some engineering companies have standard specifications that always include a specified corrosion allowance and/or increased minimum thicknesses or both.

 

[HTURKAK]

Corrosion allowance is not a mandatory requirement for AWWA D100 standard. However copy and paste of the relevant clause at Appendix A

Corrosion Allowance and Protection
A.3.9.1 General. Careful consideration shall be given to the proper allowance for corrosion. This allowance will depend on the corrosive nature of the stored
water, the proximity of the tank to salt water or other causes of atmospheric corrosion, and the care with which the paint or other protection will be maintained.

Apparently this allowance shall be considered depending on the corrosive nature of the stored water, environment ..
Pls consider other requirements such as painting, CP, galvanic corrosion and isolation of dissimilar metal contact.