Anchor Flange 3

[DooDSamurai]

Hi, I have a question about anchor flange. As far as I know every buried pipeline here ranging from 20km to 800m uses anchor flange as shown in the image. Is it necessary or redundant even if the accompanying above ground piping have expansion loop or does it protect the riser? Sorry if the questions are simple. I am just starting out.

 

[Wes-in-WV]

Pretty new myself, but I've seen large blocks of concrete buried and used to absorb forces in a line (thrust blocks). Looks like your anchor flange has a block to go with it. From the point of view of pipe stress, I would imagine you'd want some fixed points along with expansion loops to handle the changes in the line due to temp or press fluctuation. Without the regularly spaced anchors, great lengths of line could expand/contract and put some stupid loads on a bend or nozzle or whatever you run into.

 

[1503-44]

Anchor flanges are mostly just a waste of time, concrete and money. If there is no motion sensitivity of pipe or nearby equipment they do nothing other than increase stress and fix the pipe in the dirt and that may even all force above ground pipe to expand into the plant. Providing flexible pipe configurations is far more efficient and IMO the only proper way to minimise pipe stress.

It is also my opinion that the insulation fitting should not be located near the riser. That is generally one of the places on a pipeline where stresses, especially bending stresses may be the highest and they are very difficult to fix if they start leaking. You often have to wait and wait and wait for a pipeline shutdown to replace them. Try to move it farther away. A place where bending moment is zero would be great.



Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Dood/ Wes,

I think you both have a lot to learn about anchor blocks. If you do a search in this forum (box in the top left corner) on anchor blocks, you will find many posts about it.

But in general, pipeline engineers hate anchor blocks, they rarely work, create stress concentrations and all for stopping movement of 15-25mm.

The forces involved can be huge when you put it into a stress analysis program and mark it as a 6 way anchor. Forces of 100- 500 tonnes are common, especially if you have any sort of temperature increase over the installed temperature. This can lead to anchor blocks bigger than a house.

The only people who think they are a good thing is piping stress engineers who like to have a fixed point coming into their system and think an anchor works. They don't. However it is still stuck in their head from decades of doing it.

Wes, the length of the pipeline is almost irrelevant. What you get for buried pipelines is that within about 80 to 150m, the pipeline becomes fully restrained and doesn't contribute anything to the expansion of the system. This is referred to as the virtual anchor. and the movement is the temperature effect of that length is uniform, but drops off exponentially from the end point. Only a good stress analysis with proper pipe soil friction can give you the movement and forces.

Also don't let anyone ask for a "free end" analysis of your pipeline. This is useless and the pipe does not have a fee end, but is connected to other piping and can give large movements which the piping engineers throw up their hands in horror.

So "Is it necessary or redundant even if the accompanying above ground piping have expansion loop or does it protect the riser?" Most anchor blocks are not required and with proper flexibility of the piping connection are not needed.

But look, if the pipeline temperature is the same as the installation temperature even I've been know to accept a nominal sized anchor block to keep the peace, but once you get into higher temperatures you need to hold your ground and tell the piping designers they need to accept a degree of movement from the pipeline entry.

But let pipelines move is the answer. fixing anything just concentrates stress and breaks pipelines.

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

 

[DooDSamurai]

Thank you for the replies. So basically anchor block are a waste of money.

I have another question. Is it justified to roll the riser to a degree say 15 meaning the lower 45 bend is 15 degree to the left of upper 45 bend. Is it possible the anchor block was placed to protect the rolling?

 

[LittleInch]

It's a little bit strange, but I've seen it done. The anchor block is just there because, as you say, that's the way everyone thinks it should be done because that's the way wee did it last time...

"Last time engineering" is quite difficult to challenge at times so good luck....

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