unleveled or uneven floating roof in maintenance position 1

[processrj]

A 72' diameter tank x 48 feet height, single deck floating roof tank has been overhauled (overall roof, support legs,and roof drain line replaced,along with some parcial repair made to the bottom plate by patching some small portions). After conducting hydrotests, we observed that the roof landed unevenly causing the damage of several tension springs and the 2" thermowell (attached to the 12" stilling well) touching the stilling well sleeve. Thinking that the drain line might be influencing this behavior we shortened it and conducted another hydrotest, which was succesfull; however, after draining the water to the operating position and filling it back to the maintenance position and draining again for inspection, we still find the thermowell touching the stilling well sleeve. What are the possible / most likely causes for this situation? Thank you in advance.

 

[IFRs]

Hard to tell. The drawing is not to scale and shows two different details for the 2nd joint from the deck.

 

[r13]

What is the function of the tension spring? Are you sure they are functioning properly all the time?

 

[IFRs]

Probably for the shoe seal

 

[r13]

Yeah, sounds right. But I couldn't find good picture of it.

 

[LittleInch]

Processrj - What EXACTLY have you changed with the drain line?

Your drawing shows two lines - is one the existing and one new in case which one is which?

I think as the tank roof falls, you are getting in a position whereby the drain line is becoming locked in position and cannot lower further without forcing the roof sideways.

Sketch out at what level you are at when the first three segments are on the floor and only the last one is at an angle. I think you will find this higher than the maintenance position.

To go lower the roof is then forced sideways.

I think you might need some level of axial freedom of movement in the drain pipe or some different length tubes.

Draw out the roof at all heights from 15 ft downwards with the pipes on the floor of the tank unless retrained by that chain or geometry.

We can't do it because we don't have all the dimensions between each joint.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[processrj]

Thanks again for the feedback. I will answer soon, but just to clarify a couple of things: The drawing shows the same line in two different positions. The line was increased in size, as I said, from roughly 68 feet to 76 feet, after we got indications that the line might could be restricting the FR movement.

I'll come back with more details. Thanks.