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Average Rim Space measurement Procedure

Wednesday, December 13, 2017   By: Archer [509] 3 Stars
Dear Elites,
Kindly let me have the procedure to arrive at the Average Rim Space of an EFRT.
Is it the average of Maximum + Minimum divided by two or the total of 4 or 8 or 12 measurements divided by the total number of measurements 4 or 8 or 12
Thanks in advance

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Wednesday, December 13, 2017   By: Tankee [235] 4 Stars
My own procedure is to measure at each pontoon leg and near center of each pontoon, add up those measurements and then divide by the number of measurements taken. If I see any wider, or narrow, gaps, I will hit those, as well. Of course, measurements are probably going to vary on every shell course and possibly within each course. The measurement can also vary from the bottom of the rim plate from the top of the rim plate. Is this for a new or existing tank?

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Thursday, December 14, 2017   By: Archer [509] 3 Stars
Thanks Sir, for the guidance.
This is for an existing tank.
The seal manufacturer has asked for the Average Rim Space Measurement and has not responded when requested for the procedure- hence this post
Thanks again

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Thursday, December 14, 2017   By: Tankee [235] 4 Stars
Depending on the manufacturer and their design, there can be some pretty good differences in rim space requirements. Once they know the rim spacing, they can give you the best seal system for that size.

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Thursday, December 14, 2017   By: DavidR@Fast.net [39] 5 Stars
Give them the data, they can do the rest. Or, give them the mathematical average. I would also give them the max and min. Seal failures are all too common because of inadequate information.

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Friday, December 15, 2017   By: Archer [509] 3 Stars
Thanks Sir,
Is the Mathematical Average of Maximum+ Minimum divided by Two or The sum of Measurements at Multiple locations divided by Two
Thanks in advance

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Friday, December 15, 2017   By: Archer [509] 3 Stars
Beg to recall the earlier post. It should read Divided by the number of measurements and not divided by Two
Sorry Gentlemen

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Saturday, December 16, 2017   By: DavidR@Fast.net [39] 5 Stars
When I calculate an average it is the sum of the data measurements divided by the number of data points.

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Sunday, December 17, 2017   By: BABRTs 973 [53] 5 Stars
Make a drawing referencing North. Take at least 8 measurements with ROUGHLY 30 to 32 feet between them. Just like on 653 settlement. This is not Theoretical Chaos Theory. Write these down on the drawing at each degree reference point. Show where the widest and narrowest readings are. The seal manufacturer can have a visual of the readings. Just averaging the number will tell them nothing if you have areas where the gap is narrow or wider. This can affect the operation of the shoes.

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Wednesday, December 20, 2017   By: Archer [509] 3 Stars
Have understood Average Rim Space concept.
Not understood Maximum & Minimum readings how it helps the seal manufacturer in designing the seals.
Please pardon my ignorance and help. Thanks

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Wednesday, December 20, 2017   By: DavidR@Fast.net [39] 5 Stars
An example might help: Lets say you have one tank whose rim spaces are 8 all the way around. You measure 10 spots and the average is 8 and the seal design is easy. Your other tank has seal measurements that are all 8 except one is 2 and another is 14. Again, the average is 8 but this seal is a much different design.

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Wednesday, December 20, 2017   By: Archer [509] 3 Stars
Thanks Sir,
I am given to understand that the seals are designed work with 4 inch plus or 4 inch minus of average Rim space, Is this correct Sir?

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Wednesday, December 20, 2017   By: DavidR@Fast.net [39] 5 Stars
Per API 650 peripheral seals and their attachment to the floating roof shall be designed to accommodate ±100 mm ±4 in. of local deviation between the floating roof and the shell. This is usually a variance on the design rim space. Some do this better than others. Some have nothing left and cant go a bit further than +/- 4 which means they dont press against the tank shell very much at +4 or cant compress any more than -4 without being damaged. If the seal is designed for 6 +/- 4 and you have 8 +/- 4 it may not work. Some vendors take the approach that this deviation is only a local change and the amount of tank steel at every elevation is the same so the seal does not really need to change its overall length. Others design their seals for a growth or shrinkage of 4 for the full circumference. Both meet the standard, but if you have a really bad tank one design may perform better. The more information you give a vendor, the better they can do for you, possibly including recommending a different style or design. My opinions only...

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Thursday, December 21, 2017   By: Archer [509] 3 Stars
Thanks Sir!
Seasons Greetings to All!

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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