Berthing Pile - Cooking Oil

[Uprising]

Hi Everyone,

We are currently designing a berthing pile, constructed from a 1016 x 25.4 thick steel pile. As-constructed drawings for a previous installation for this client specifies 40 litres of cooking oil be poured into the pile after installation and then sealed with a HD Galvansed 2" BSP air tight plug flush.

I don't understand the reason for the cooking oil (presumably some type of corrosion protection?) or any guideline / specification that specifies cooking oil for berthing piles / steel piles.

Is anyone able to provide some further advice on why it is or should be provided?

Thanks,
Luke

 

[romke]

the only reason that springs to mind is that (some) cooking oil can contain a large amount of fatty acids that due to their polar nature adhere very well to steel and maybe better than mineral oil. however, from a point of view of corrosion protection, they are certainly not optimal and maybe worse then standard lubricating oil. if long term corrosion protection is the goal, I would prefer a dedicated fluid especially designed for that specific purpose.

maybe you better ask the client why this particular was specified in the past.

 

[IRstuff]

Do they specify the type of cooking oil? There's a pretty big range of viscosities for oil.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[BUGGAR]

I note these were as-built construction drawings. Do you know the as-built history? Like did contractor drive a thin-wall pile and make up for the lack of corrosion resistance with a little cheap help from a local restaurant?

 

[IRstuff]

So, instead of paying to get rid of used oil, they got paid for it?

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[Uprising]

The detail is shown below specified in the drawings is provided below.

AS4997 Guidelines for the design of maritime structures specifies that hollow members should be sealed to prevent corrosion on the inside face. This is an open-ended steel pile which is embedded 15m into stiff clay. My thought is maybe the oil acts as some kind of seal/barrier to prevent salt entering the sealed void inside the pile.

 

[Compositepro]

The unsaturated fatty acids slowly react with oxygen. It may be used to reduce corrosion by acting as an oxygen absorber over a long period of time. Oxygen is a critical part of the corrosion process. Cooking oil is probably specified to avoid any issues with possible environmental contamination.

Cooking oil is a good lubricant over the short term because it wets metals well but in will create a varnish layer, with time, through reaction with air. Linseed oil is used as a varnish and oil-wetted rags are prone to spontaneous combustion due due to the oxidation reaction.

Also, corrosion is most severe at any air-water interface. Oil floats on water and will protect this ares most.

 

[romke]

one more question - you need to pour in 40 liters of oil. will the pile then be completely filled or is there still some room left which then would be airtight sealed by the plug? or will some air be sealed in as well? if the latter is the case there still will be a volume that may be prone to corrosion that is not protected by the pured in rust preservative.

from a environmental perspective the prescription also is remarkable. it may be so that the surface the pile is driven into may be clay, but that does not necessarily means that it is fully impermeable for a fluid. thus, some seepage may well occur and thus "oil" (be it "cooking oil" or mineral oil) will disappear into the environment.

 

[SDMAX]

I have seen cooking oil used in the outermost annuli of offshore wells. The annulus was exposed to the sea near mudline and this caused the water level in the annuli to rise and fall in time with tides and wave. As Compositepro mentions, corrosion is most likely in this oxygenated layer and the cooking oil was poured in to provide a cap on top of the water to lower the oxygen content and reduce corrosion.

Cooking oil was used in preference to any other oil due to the fact that it would break down decompose over time, so any leakage or spillage during the top up operations would not cause a reportable oil spill.

I was told that it did work, but not as well as when they used diesel oil.

 

[chicopee]

Would this procedure constitute an unlawfull disposal of oils in navigable water per EPA regulations?