Those painting and insulation works will be performed with main-1lifts and take 5 days as minimum in condition that works at all the Racks are being performed in parallel
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(1) I used the future tense because your English translation created the impression work had not been done yet. After seeing the Russian version, I understand that work was started, but not completed.
(2) A better translation of an автовышка is “aerial work platform”. (3) Now that I have seen the Russian text, I realize, as you say, there is no agreement to finish the work within five days. Instead, the text is only giving information that it will take a minimum (not less than) three days to finish the work.
According to dictionaries, the Russian word “эстакада” can be translated many ways: viaduct, trestle, gantry, scaffold, walkway, etc. Each of the English words refers to a different thing. If possible, send me a link to a photograph of what “your” эстакады look like, and I will try to choose the correct word in English.
Please note that I translated the Russian word "при" with a simple “if”, because I don't think the word "при" imposes an obligation. Let me know if that’s not right.
So now I suggest:
At “эстакадах” Nos. 1, 2 and 3, there are piping sections whose painting and insulation have not been completed by your company. The completion of the painting and insulation will be performed using aerial work platforms, and will take a minimum of five days if the work is carried out simultaneously at each “эстакадах”.
Corrections in red. Stylistics in blue.
There are some piping sections at the racks No. 1, 2, and 3, where your company will paint and insulate  the pending works.
Said painting and insulation will be performed with main-lifts,  and take a maximum [?? 3] of five days, on condition that the work at each rack be performed simultaneously. 
 I used the future tense "will paint and insulate" because the next sentence regarding painting and insulation is in the future tense ("will be performed").
 I don't know what a "main-lift" is in this context.
 Normally a contract will state a maximum amount of term to complete a job. Did you really mean "minimum"?
 "in parallel" was not readily understandable. I concluded you meant "simultaneously" (occurring at the same time).
If you think I misunderstood you in any way, please write again, paraphrase in English, or write what you want to say in Russian.
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