Pack Rust on Steel Bridges
Pack Rust on Steel Bridges
(OP)
I'm working on a bridge rehabilitation project for a viaduct constructed in the late 40's/early 50's. Some built up floorbeams - photos attached (one photo is an extreme case) - have been affected by pack rust/rust pact/impacted corrosion – call it what you will.
The client is looking for specific remedies to this problem. Their opinion is that the traditional remedy of blast cleaning and painting won't work. In the 80's I worked on a project in Ohio with the same problem. The ODOT spec, in addition to blast cleaning and painting, called for the installation of an acrylic caulk between the steel plies prior to painting.
I would like to know if others have any successful methods of dealing with this, in terms of a coating or sealant.(From a structural standpoint there are locations where we may have to remove rivets; then remove the rust; heat straighten; then install bolts.) There's not a lot of information out there; although I came across differing opinions. One article recommended "meticulous cleaning" (that's not going to happen) followed by an acid neutralizing paint. Another said water blasting is the worst thing since it will only entrap the water
The client is looking for specific remedies to this problem. Their opinion is that the traditional remedy of blast cleaning and painting won't work. In the 80's I worked on a project in Ohio with the same problem. The ODOT spec, in addition to blast cleaning and painting, called for the installation of an acrylic caulk between the steel plies prior to painting.
I would like to know if others have any successful methods of dealing with this, in terms of a coating or sealant.(From a structural standpoint there are locations where we may have to remove rivets; then remove the rust; heat straighten; then install bolts.) There's not a lot of information out there; although I came across differing opinions. One article recommended "meticulous cleaning" (that's not going to happen) followed by an acid neutralizing paint. Another said water blasting is the worst thing since it will only entrap the water





RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
I don't recommend re-posting this to the paint/coatings forum. Any of us that are familiar with coatings, corrosion, etc. will be on this forum and have already read your post. If the others are like me, you haven't received any responses because this is a complicated issue that has a lot of implications relative to acceptable design practices, approval to industry standards/codes, acceptance by local/state/federal governments, etc. I concur with hokie that it appears some of this needs to be disassembled to remove pack rust. I also concur with the advice you were given relative to water blasting.
RE: Pack Rust on Steel Bridges
I met with the client today & this was one of our discussions. Right now we're leaning towards some type of power tool cleaning followed by heating the affected area to approximately 250 F to dry it out, then sealing it. There won't be any disassembling of the member other than an individual rivet here & there - it's just that there too many potential complications - and no attempt to heat straighten anything.
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
Urethane is a better choice than acrylic, though I suspect the old ODOT spec was a solvent-reduced acrylic, not the common waterborne acrylic latex. Solvent-reduced acrylic wouldn't be a bad choice, urethane's just better. I wouldn't use a waterborne acrylic.
Pack rust is rarely "solved" for the reason mentioned earlier - you have to disassemble the plates to do so. I have seen one project where pack rust was fully removed in some limited locations because gusset plates were being removed and replaced with beefier ones.
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
I would actually like to see more aggressive pack rust removal, but the structural guys have expressed significant discomfort at having more non-contact area.
RE: Pack Rust on Steel Bridges
In 10 years I probably won't be interested in pack rust anymore.
RE: Pack Rust on Steel Bridges
The first areas painted on the earliest project don't seem to have any issues with the pack rust areas yet. We do have some limited areas on the steel with minor breakthrough on some edges and bleed out of back-to-back plates. Not associated with pack rust. Not surprising to see them, given the complexity and size of the structure. Not enough for the driving public to even notice.
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
hokie - There's a guideline we use for rivet replacement based on the head size (been floating around on NYSDOT projects for about 40 years) but stretched is a different case; I've never seen it addressed. This leads to the concern about non-contact areas because there's a limit to how much separation a bolt(s) can suck up. It looks like we're thinking the same thing.
RE: Pack Rust on Steel Bridges
1) I notice rivets which look significantly corroded (metal loss) or deformed.
2) I call or email one of the structural guys and ask them to come evaluate and to "use their engineering judgement."
My focus is paint and corrosion. I believe they have guidelines as well, but I haven't gotten into that.
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
After any prep work has been carried out, is there any testing done to check the integrity of the plates etc (Example U/T) as far as load rating capability?
I have no experience in this field and was just curious.
Cheers
RE: Pack Rust on Steel Bridges
On a painting contract, you have to hope the inspector is diligent, and if he sees something he3'll say something.
In NY all fracture critical and fatigue prone details receive 100% hands-on inspection during the biennial inspection. I've also done bridge inspections of some major long span structures on which mag-particle and U/T testing was performed on certain fatigue prone details
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges
I read those notes to require the replacement of all rivets which are stretched by the pack rust...Note 7.
RE: Pack Rust on Steel Bridges
Although it doesn't explicity state it; I read it that way also.
RE: Pack Rust on Steel Bridges
RE: Pack Rust on Steel Bridges