Crevice Corrosion aka Pack Rust 1

[connect2]

Looking at a RR Bridge from 1929 riveted through plate girder with ballasted concrete/steel diaphragm deck. There's 'pack rust' between the bottom flange plates and in some locations the rust is up to 3/8" thick with the pack rust evident pretty well the full length. Does anybody know if there is a correlation between pack rust thickness and depth of corrosion 'pit' behind the rust and inside the plates? I am using AREMA Chapter 15 2018 for rating.
Thanks.

 

[EdStainless]

No, there isn't. The only way to really know how much metal there is is to take it apart.
The crevices are filled with a mixture of corrosion products and debris.
So depending on how much stuff collected vs how much flushed out you just can't tell.

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P.E. Metallurgy, Plymouth Tube

 

[bridgebuster]

I agree with EdS; no easy way to estimate the loss of section without removing it; of course, it's not easy to remove. On a recent project, we called for pack rust repairs on riveted plate girders. Generally, the ironworkers could only get 1 to 2" in from the edge of flange; they're using air tools. Perhaps the section loss isn't too bad. I've inspected a lot of rusty steel bridges; sometimes after cleaning off a thick layer of exfoliation, there was only minor loss (sometimes worse). You could assume a certain percentage is lost and go from there.

 

[connect2]

Thanks above, some comments.
Cost of removal removal of a cover/flange plate would be very high and not that simple for sure.
So Lamellar/Exfoliation corrosion is one thing the crevice/pack rust another. The crevice corrosion is occurring between the 3 plates that make up the bottom flange(s) of the through plate girder. Tension. My concern is with the crevice crack and proximity to the rivet holes re fatigue.

 

[Ron]

connect2...your concern is well-founded. Ed and BB are correct....there is no short-cut for this. Take it apart.

 

[BridgeSmith]

If you can get past the rust on one side of the flange, you can use an ultrasonic thickness gauge to find the thickness of the remaining steel. We have one that we use for bridge ratings.

Edit: I just noticed you said there were 3 plates. That makes it a little more difficult. For the middle plate you could assume the same depth of rust loss as you measure for the outside plates, or take the conservative route and assume a greater depth. There's alot of engineering judgment in rating old bridges; it comes with the territory.

 

[connect2]

No simple solution but yes as HR10 mentions Ultrasonic Measurement is likely the only Non-Destructive Testing possibility that could give an indication of the depth, shape, direction of the crevice pit.
Taking it apart to have a look is most reliable, say all, but hadn't planned to start the remediation/repair that quickly!
So yes applying the 'Art' would be that there's a loss of about 20% of the section, or 3/16" crevice depth occurring in proximity to rivets and go from there.
There's so many cases of 'pack' rust was just hoping that perhaps there was some data/report somewhere that correlated pack rust thickness to crevice depth.
Thanks all.