Sand Blasting and Painting Fabricated Steel Frames

I would venture to say 5 to 7 years is added to the life of the mill if painted and maintained properly. Not to mention the savings on repairs to replace rusted out part of the structure. Paint is still cheaper than the future repair cost when it begins to rust out.

We have a saying in the Painting industry that a paint is as good as the surface you put it on, It is a wellknown fact that prepaiting the surface by sandblasting will increase the life of the paint coating at least five trimes, saving largely in maintenance and repainting and down time.

vshwn7@aol.com

I highly respect the 25 year in steel and only add the following items to further support:

Water is not the probably as much as water+air then dry then water and air - in steel sheet piles - below the water line - permantely the steel survivedquite well...the intertidal zone - highly corrosive environment of water, splash, air and salt.

Similarly even with a good paint car job people forget that if you have the dew+calcerous dust(cement dust the worst)+air+ drying the final evaporate is highly caustic and with repeated condensation-dew and drying the same cycle will eventually corrode its way through even the paint.

Therefore, please blast-hopefully with slag grit rather than silica sand...paint...wash down...repaint in good maintenance practices - you got the machine hopefully for 40 (>25) years of good service/productive life in one of the harshest environments...oh take care of the poeple that run/maintain the machines also.

TOM

I will recommend epoxy paint as final coat with suitable primer. Epoxy paint is resistant all chemical, water etc corrosion.Of course it is expensive but long lasting. May be paint mfr. can give you better suggestion.

Epoxy paint is good.

In the oily environment of machinery I would take further and go with powder coating.

Powder coating is more resistant to wear it's hard to scratch and mar the surface than it is for epoxy paint and the price between the two is about the same.

We do both. We epoxy paint most of the parts for our machinery and when we have items to paint in bulk we powder coat. We could epoxy paint our bulk items but after awhile the painted parts will be all scratched up and chipped, where as the powder coated parts after going through the same abuse will still have a good finish.

I like coal tar paints down low in really dirty grimy places it is hard a a rock.

I agree that coal tar is very protective, but the air quality folks have clamped down on the VOC and bitumen emissions. Epoxy acrylic seems to be the coating of choice in wastewater environments.

Would hot dip galvanized handle the environmental conditions?

Expected life of steel product is 25 years. (thats how long the govt says we have to maintain records of each heat.)

unprotected steel will be subject to environmental conditions including humidity, despite your best efforts to put a rainbow sheen with oil on every puddle for miles around.

once rust and pitting starts,it can lead to severe failure modes such as crevice corrosion and intergranular corrosion.

You paint and protect everything so that the lowfrequency high probability events that lead to rust get stopped by the barrier.

An alternative that your design engineers apparently ruled out was the use of self healing steels like cor ten.

http://www.gim.bnl.gov/misc/envtest/dlcal/corrosion.html

milo

http://www3.interscience.wiley.com/journal/109665443/abstract?CRETRY=1&SRETRY=0

Probably specified by the EOR (engineer of record) and in the contract requirements for new building construction.

Retrofit / rehab - painted to begin with, would you need to rehab??

Well, you have a lot of good ideas already. I would leave you with one other suggestion. Abe Linclon said "Give me six hous to chop down a tree and I will spend the first four sharpening the ax." This philosophy can be applied to your paint dilemma.

The durability of any coating, is enhanced by the preparation of the substrate. There are inherent differences in coatings, some better than others, but preparation is very important. The sandblasting is very important. There should be care taken when doing this. You can perform a standard Commercial sandblast or a MIL spec blast which is much more extensive. Whatever you do, it should be done carefully. Someone admonished against a silica sand blast, but I have always had good success with silica sand. You can use shot or grit if you like, but sand is usually more readily available and cheaper.

Another suggestion given earlier was the use of a powder coat. At the risk of sound ing ignorant, which I am regarding powder coating, I though that proces required baking or heat curing the coating. They must have some type of portable machinery for that process. Those who do that can instruct you more fully.

Good luck.

The durability of any coating is enhanced by the preparation of the substrate.

DING! Preparation reminded me of the SSPC standards and specs issued to use for wastewater environments.

You may have to buy a copy of the standard for recommendations on surface preps, but it also could be money well spent.

If there are welds in the structure I will give you five years at most before failure.

Growing Up in New England Dad used to pour waste oil around fence posts.

Wind ( O2) and water invariably would get to the untreated areas and the paint

would fail and doug fir posts would shear under blowing snow loads.

Unless you plan to retire in the next five hire a SSPC Certified contaractor and

get them done correctly which will include a sspc 10 white metal blast ! Oils do not prevent the O2 H20 exposure rates and generally mask the problem areas.

Powder coat properly applied after white metal bast is the most expensive but nearly permenant coating

as is some conversion coatings. SSPC and Powder Caot assoc Mag has some great data so does a guy called Mike Craven at a company calle Black oxide in So Cal.

PS Pouring Used Oil on your fence posts is a federal crime since the 1970's in the US.

Dad made me!

Paint those rollers!

I don't mean to be confrontational but, where did you come up with the failure rate of 5 years, if the structure contained welds?

If the structure was manufactured / fabricated with welded components, it should meet the criteria of MBMA or at least an AWS certified welds (welded by certified welder to AWS standards) and last longer than the base metal itself!

Any steel frame that resides indoors will degrade (rust, etc.) at a very slow rate with "normal" element exposure expected inside.

If exposed to coolant, chemicals, etc., obviously would effect degradation.

Yes, painted or powder coated members are preferred and typically specified in design documents to slow elemental degradation and usually spec'd to SSPC requirements.

We have manufactured steel buildings for over 50 years and supply the beams and columns to customers with a primer coating only. They may choose to finish coat or not. A majority do not.

ALL ARE STILL STANDING!

Thermal spray them with Al. considering that you blasting them anyway!

Let me add one additional comment. Vibrations and shock loadings would seem to be a regular part of the operation of rolling Mills plant. When a steel part develops a crack, there is a distinct color that develops at the site. If the entire structure is allowed to develop the appearance of nondescript bare metal, any change will be harder to notice. An even coat of any color than a rust color will allow a casual observer to see the color change at the crack location. It may not matter much, until a crack develops. Good luck.