SEVERE STP corrosion internally on Diesel

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PatSmyth
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Re: SEVERE STP corrosion internally on Diesel

Post by PatSmyth » Mon Dec 04, 2017 11:40 pm

Not only is there the need for a change in the technology required to remove all water (free standing and emulsified), namely next generation filters with a 92% efficiency in removing emulsified water as tested against SAE J1488_201010, there is a new installation process required. I did not describe the process in my previous post. When we install a system, we install our intake right to the bottom. We *want* to suck up all the free standing water and sludge from the bottom. The regular operation of the system will continually remove any newly created sludge or free standing water. In this manner we keep the fuel dry, and clean.

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CherokeeUST
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Re: SEVERE STP corrosion internally on Diesel

Post by CherokeeUST » Tue Dec 05, 2017 8:13 am

Pat, I'm not following your summary.

Where do filters come into play in a fuel storage tank? Filters are in the dispensers, but that won't stop corrosion in the tanks.

The drop tubes are required by regulations to be 6-12 inches from bottom. Intake tubes are usually 4-6 inches from the bottom.

Or are you just telling everyone how your fuel cleaning process is greater than all other fuel cleaning processes? Yeah, I think you are. I'm kind of slow. I see now..... :roll:
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Re: SEVERE STP corrosion internally on Diesel

Post by ZMiller » Tue Dec 05, 2017 8:40 am

"Intake tubes are usually 4-6 inches from the bottom" Therein lies the problem for water and debris over time to become resident. The solutions may incorporate initiation of better tank bottom maintence procedures and surely a better coalition and filtration of fuel. Particularly with Diesel and the percentages of Bio Diesel blended filtration may capture and remove entrained water that is in the actual fuel and not hanging around at the bottom of the tank.

Maybe after the tank has been cleaned we need to lower the intake to the bottom of the tank.
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Re: SEVERE STP corrosion internally on Diesel

Post by bugbuster » Tue Dec 05, 2017 9:07 am

Dropping the STP intake to the UST bottom would increase the water and sediment load reaching the filter. If the filter is reasonably efficient (i.e. at least 98% effective removing particles >2 microns & water) it will need to either have a considerably greater capacity (surface area) than current dispenser filters, or filters will be replaced at a rate considerably faster than they are now. As it is, operators complain about short filter performance life.

Moreover, per Cherrokee's comment, codes define the distance between UST bottoms and STP intakes.

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Re: SEVERE STP corrosion internally on Diesel

Post by stuppid » Tue Dec 05, 2017 10:59 am

Tank manufacturers demand a minimum clearance between the submersible pump and the tank bottom based on tank diameter. The way it has been explained to me is that in a large seismic event the tank can deflect and if the submersible is too close to the bottom it can contact and damage the bottom of the tank.


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Re: SEVERE STP corrosion internally on Diesel

Post by bugbuster » Tue Dec 05, 2017 11:15 am

That makes sense.
Additionally, owners face the tension between minimizing the stagnant zone (maximizing product utilization) and maximizing filter life (minimizing water & particulate loads reaching dispenser filter). I've calculated that for each 10% flowrate reduction, operators enjoy approximately $125,000/year/dispenser opportunity cost.
Assumptions:
1) High traffic, urban locations - 4h/day during which vehicles line up to get to dispenser.
2) 30 min/h actual dispensing (30 min/h folks paying, moving cars, etc.)
3) $3.00/gal fuel price
4) 10 gpm maximum flow rate

Obviuosly, the longer one can maintain >7 gpm dispenser flow-rate, the lower the opportunity cost impact.
By some (filter manufactuirer) estimates, retailors typically wait until they are getting <3 gpm to have dispenser filters changed.

Bottom line: there are engineering, fuel quality, regulatory, and commercial factors that need to be considered before specifying STP intake distance from UST bottom. Reiterating an earlier point, the best filters will only remove contaminats from fuel that passes through its element(s).

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Re: SEVERE STP corrosion internally on Diesel

Post by PatSmyth » Wed Dec 06, 2017 8:07 am

Our system is a standalone fuel polishing system. We turn over the tanks fuel volume a set number of times a month. Once the tank is cleaned, the scheduled filtration of the tank continually removes any particulate, sludge, free standing water, and emulsified water that may have accumulated or grown since the last cleaning. It is key that the intake is right to the bottom, so the flow of the fuel caused by the filtration process moves the sludge and water to the intake. We could use a STP, or just an intake pipe connected to a pump collocated with the filter above ground.

The filters are sized by tank volume, but in general are very large.

If we are being added to an existing tank, we first run 7/24 with only particulate filters until we are "clear and bright". From then on in we use the emulsified water filters on the set schedule.

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Re: SEVERE STP corrosion internally on Diesel

Post by PatSmyth » Mon Dec 11, 2017 12:10 pm

A question for Bugbuster, regarding his post on opportunity cost, Tue Dec 05, 2017 12:15 pm.

What would the effect on opportunity cost be if the fuel polishing system keeps the fuel so clean that the dispensing filters are rarely changed out? Granted, I don't know how often they are changed out in reality, but we use .2 micron filters, and typically have particulate results well below 18/16/13, so should have an impact on when dispensing filter are changed.

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Re: SEVERE STP corrosion internally on Diesel

Post by bugbuster » Tue Dec 12, 2017 6:50 pm

Fair question, PatSmith.

First, I'll acknowledge that my opportunity cost model is a bit of an over simplification. Although I've encountered the rare exception (i.e., retail site managers running dispensers for prolonged periods at < 3gpm), I'd be surprised if flow rates <7 gpm are tolerated by most retailers.

The key here, is that the longer a retailer can keep flow rates as close as possible to 10 gpm, the smaller the opportunity cost economic hit.

In direct response to your question, if a retailer is using a cost-effective (given the opportunity cost side of the equation, it seems that a retailor would be hard pressed to take actions that were not cost-effective) mix of condition monitoring and predictive maintenance, they will reduce their fuel sales opportunity cost. Reducing particulate loads reaching the dispenser filters is no doubt beneficial. The actual return on investment (ROI) would depend on the cost of replacing the kidney loop's filters, maintaining the filtration unit, sending the used filters to a hazardous waste handler, and the impact on dispenser filter pressure differential (flow rate) histories. Field testing would determine the impact that side-stream (kidney loop) filtration would have on dispenser filter life (>= 8 gpm). A 5x increase in filter life represents a greater ROI than increasing filter life by 1.5x (50%).

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Re: SEVERE STP corrosion internally on Diesel

Post by CherokeeUST » Tue Jan 23, 2018 8:40 am

Addressing Tank Corrosion

Lower levels of sulfur in today’s diesel fuel supply bring increased risk. What you can do—and what NACS is doing—to address the problem.

http://www.convenience.org/YourBusiness ... osion.aspx?
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