Minimum Umbilical J-Tube Diameter

[suraiya]

I'm a project engineer currently working on a project designing an SSIV (subsea isolation valve) system. The umbilical size is 4-inch, and the pulling head is about 6-inch but the pipeline/subsea consultant has proposed that the umbilical J-tube diameter to be 16". To me this seems to be an oversizing and 12" should be sufficient. But the consultant is saying that they are worry about the bends (which is actually already 5D compliant). Am I being too optimistic or the consultant being too conservative? Is there any design guideline, standard or codes that can be of help in determining the minimum diameter for J-tube?

 

[LittleInch]

suraiya,

you really should know by now that triple posting is not allowed.

To address your question - There is no standard or code as each one varies.

The key points when deciding the diameter of the J tube are:

Length of the "solid" pull head which then needs to navigate the bend
Minimum bending radius of your umbilical - a key consideration and each one is different
Maximum pull force on your umbilical - same as above
Radius of the pipe bend able to be accommodated (bigger radius - more unsecured)
Weight of pipe on structure.
effect of J tube on structure (wave loadings etc)
You can get some J tubes where the lower section and bend is one diameter and the main (straight) riser section is a smaller one.

So basically "It all depends" on data you haven't shared with us, but I hope it gives you a bit of idea about some other elements which go into the decision making process.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[London]

See if you can creat a drawing demonstrating to the installation contractor that the shackle, pulling head, and umbilical can fit around the bend of the tube.

Also should check the pulling force from the winch in the inside of the bend, and that you have a place for the pulling winch.

As LI mentioned, the length of the head is significant.

Bellmouth to avoid any snagging.