Pipe Piles - Coal Tar Epoxy Coating

[JoelTXCive]

I do not have a lot of experience with pipe piles, but we have a project where the soil conditions were so poor that my normal go-to of drilled shafts will not work.

The geotech has recommended 18" x .375" wall thickness driven piles.

These are dry-land piles in a fresh water environment. For corrosion protection, I specified a fusion bonded epoxy for the top 8ft of the piles.

The contractor has submitted an RFI to use 16mil coal tar epoxy for the entire pile length (~50ft).

I have a conference call on Monday to discuss with the contractor.

Any questions I should ask? Is the soil-to-pile friction coefficient different?

Thank you in advance.

 

[MotorCity]

Seems to me the coal tar epoxy (or any coating) would not survive the driving process. I've never spec'd a coating for steel piles. Usually we increase the required wall thickness by some nominal fraction to account for corrosion and the top of the pile is usually embedded or encased in concrete.

 

[JStephen]

Galvanizing might be another option to look at. It depends on where you're at. I think the local galvanizers can do 50' by dipping one end at a time.
Any coating might help, but I also would not have a lot of confidence that the coating would survive intact.
Check if either coating manufacturer has any input on the topic, they can likely tell you the toughest coating available.

 

[JedClampett]

There's a lot of coatings available (and used) on sheet piles. It seems that the installation of pipes and sheets (being pounded into the ground) are similar enough. And these are driven into brackish water, so nasty.
Here's a schedule. Note that there's three coats of material with the second one applied twice:

Wasser Coatings: MC-Zinc 100 and MC-Tar 100
Tnemec: Series 1 Omnithane and Series 446 Perma-Shield MCU
Polyval (Xymax): Mono Zinc and Mono Guard

I'm guessing the MC Tar is a coal tar of some kind. If the material they're suggesting is recommended for underground installations, I'd consider it.

 

[dik]

Many coat tar epoxies are carcinogenic... be carefull.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hokie66]

My first deviation from drilled cast in plate concrete straight shaft piles would be to enlarged base (Franki) piles if the equipment is available. If not, then driven precast piles.

 

[dik]

Screw piles are becoming more prevalent in these environs... We have a highly plastic clay. Often for loads less than 10K, for decks and ramps, etc... but using them for 150K on my latest project and have used them for supporting six 400K transformers. Because our soils are 'feldspar' based the clay is not very abrasive; it is relatively 'soft'. HDG works really well.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[HTURKAK]

The common practice is , adding corrosion allowance ( CA ) to the wall thck. rather than epoxy coating . For example, you may look DIN 1993-5 for corrosion rates as a function of the aggressive medium and the pile exposure.

The coating may be destroyed during driving so, one cannot be sure for the coating is in good position. I have witnessed a heavy coating ( coal tar + rock shield ) in a country.

My suggestion will be, add CA for the whole pile and PE or epoxy coating for the uppermost 12-15 ft.

 

[TLHS]

I instinctively don't trust coatings for driven piles. It's always seemed like you're definitely getting scratches and unless is galvanizing or something else sacrificial, you now have a route in. There's also no way to do maintainance. That being said, if you are doing a pile coating, coal tar epoxy has been used reasonably extensively. Watch that you'll potentially have frictional reductions, which may be the case as well for other paints.

I agree, though, that a corrosion allowance is typically the route I use. It's practical, doesn't create issues with an additional coating sub and avoids the touch up issue. When I have done coatings, it has generally been for above ground portions of exposed piles and maybe the fire couple of feet below grade.

Also, I generally find that pipe pile section size is governed by practical reasons rather than fully utilizing the steel strength, so you may already have some sacrificial thickness that can be safely used as a corrosion allowance. Unless you're going into rock with what you've mentioned, I suspect you've got some thickness to play with? You might not need to change anything at all.

The Eurocode that HTURKAK mentioned is what I'm mostly using for my corrosion rates now, because it's the most authoritative general use source I've seen. I think there's some stuff in NAVFAC or other US military guides, and there are dozens of studies by US transportation agencies.

 

[TLHS]

Also, you might find this interesting:

https://www.mvn.usace.army.mil/Port...ver_SteelPileCorrosionProtection_12162009.pdf

 

[MTNClimber]

I’d like to add that piles aren’t usually transported and handled like an epoxy-coated plate girder. I’ve had coal tar or epoxy-coated piles show up with defects in the coating from the application, rubbing from transportation, improperly handled and stockpiled, all before the pile touches the hammer. Sacrificial steel takes away that awful conversation of field touch-ups, which can delay pile driving to allow curing, while the contractor points out that it will get scratched on the way down.

 

[TLHS]

Sacrificial steel takes away that awful conversation of field touch-ups, which can delay pile driving to allow curing, while the contractor points out that it will get scratched on the way down.

Man, I feel this one. There are moments in projects where something becomes a big deal that was a small thing in your head in a design. The moment puts you face to face with the consequences of the decisions you make in design where you now have to decide "man, was this really worth all this trouble?" and "Does this have value?" On the opposing side, though, you have the weight of the money that got spent getting to this point and the fact that you know you thought this had value when you were sitting in an office six months ago. Even better when you're potentially delaying work because piles were supposed to go in that afternoon or the concrete trucks are on the way.

You know that whatever comes out of your mouth, the contractor's going to think you're a twit, because either you're enforcing a thing they think is dumb (and they might be right about), or you're agreeing with them and saying that the thing may not have mattered in the first place.

I have mostly settled into a default answer of "I hear what you're saying and you might have a point, but we have to stick with the intent of the spec at this point. If you put a cost to it in writing I can look at it."

But I've definitely had people pleasing moments on these items where I made things much harder on myself. They're also the types of interactions you can leave feeling like you're wrong regardless of which route you pick, because they tend to be grey-er types of areas. On occasions where you decide to loosen your requirements and it leads to problems down the line, though, it definitely feels worse. I think I've come to peace with the fact that it's less concerning to worry that you're being a pointless hardass than worry if you're compromising to reduce conflict. The engineer in me, though, always wants to try to re-evaluate on the fly.

These are the types of moments that drive engineers to do 14 rounds of markups on note sheets because every time they see it in final print they see a couple of words being interpreted weirdly or another couple of sentences that should be put in.

 

[LittleInch]

I'm amazed you can get CTE. Pipelines stopped using it over 20 years ago due to the carcinogenic effects. And FBE became so much better.

If these are friction piles then yes, that's a must ask question.

Also why 50 ft? Pipes usually come in 40 ft lengths so a weld for an extra 10 ft of pipe vs a few more piles?

Piling technique to be used?
Type of soil and solids / flints/ gravel content?
Or is this barely solid silt / slime?
Any planned CP?
Is your design allowing some corrosion in the lower 42 ft of pipe?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[phamENG]

What does "dry land piles in a freshwater environment" mean? Do you mean they're piles typically used on land, but you're driving them on the edge of a lake? Or they're under a building but near a lake/river? If in the water, you should be okay with a coating - as long as any splash zone or area of wetting and drying is covered along with area exposed to any sort of water flow, corrosion will be minimized. You could also go with a post-installed wrap.

It's still typical in my area for structural steel "below grade and/or top of slab elevation" to have two coats of coal tar epoxy. Not something I'd ever questioned much, but this is making me think about it. Coal Tar Epoxy has the advantage of being spray/brush applied after surface prep. Fusion Bonded has to have surface prep, preheat, coating, and then curing. Any good alternatives for this application?

 

[dik]

Thanks LI... didn't know about FBE. I had to look it up. Not into piping, but it's good to know.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleInch]

FBE is the default pipeline coating.

Initially it had a bad press, delaminated and created corrosion cells underneath!

But now it is pretty good, but does need really good grit blast and controlled conditions to get the powder to melt just right at about 200C. usually in layers about 0.3 to 0.5mm thick. Actually feels a bit "rubbery" and is definitely difficult to peel off.

CTE sticks to anything, but is quite a lot softer. Prob ok if you get no shear on the pipe coating, but tends long term to kill those applying it,

So a bit like creosote - great for your fence or shed if applied every few years compared all the modern stuff, but not great for the person doing it every day.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

Thanks LI... didn't know that.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

Coal Tar Epoxy coating has been basically banned in some countries for years for the reason identified by LittleInch.