Anchor Block Sizing/Anchor Block Stiffness 1

[Rasoolbc]

Dear friends,
I am doing some modeling in Caesar II to calculate the maximum force applied on an Anchor Block due to the thermal expansion. After modeling, the results has come up with 62 kN force for the Anchor Block for 8 inch steel pipe (APL 5L X65) and 45°C operating temperature at 11MPa pressure.

In Caesar II, an Anchor Block is assumed to be fixed without any movements and/or rotations; however, I think in reality it has a movement of about 3 to 5 mm (rough assumption). Then I believe that we need to consider stiffness for the Anchor Block to make modeling as close as possible to reality.

Has anyone done any similar modeling before? What stiffness for the Anchor Block gives me up to 5 mm displacement?

Your sharing knowledge with me is greatly appreciated. Cheers.

 

[BigInch]

1/stiffness1 = 62 kN / 3 mm = 20,000 kN/m
1/stiffness2 = 62 kN / 5 mm = 12,000 kN/m

Independent events are seldomly independent.

 

[Rasoolbc]

Hi BigInch,
Thank you for your hint. Have you done such modeling before? Have you come across similar things before?

 

[BigInch]

I've been trying to eliminate anchor blocks ever since pipe stress programs requiring anchors to do their analysis have been in existance and became popular with some mideast pipeline operators. Before than, nobody used them very much. I'd recommend that you call yourself a "flexibility engineer", then learn how to develop flexible connections to pipelines and get out of the anchor block business. No future in pipeline anchor blocks as long as I'm around.

Once pipelines are buried, they don't move much as you've already discovered. We hardly ever use anchor blocks in the western hemispheres and in Europe. I'm cleaning up their use in the mideast. Saudi Aramco has finally admitted that since the 80's their anchor blocks have increased in size, even more than doubling in size for the same pipeline loads. That was reported in thier Technology mag, in 2011, I think it was.

Download US Army Corps Of Engineers publication TM 1110 and you'll find out that the American Lifelines and ASCE methods for calculating soil friction assuming it is the result of treating soil as a hydrostatic load based on the weight of soil x friction factor yields about about 1/2 of the real values. That method does not take into consideration the wedging effect of soil particles near the pipeline moving into the particles ahead of it as the pipe moves. That causes a wedging and constricting effect which increases the net friction factor as each ring of soil particles behind wedge into those ahead of them. That method is also popular in concrete pipe design manuals. Those guys have been burying pipe in the ground for over 200 years. I think they know what they're talking about, because I see the same thing every time I see a pipe exiting the gound... not much movement, if any at all. 5 mm to 10 mm maximum, then no further movement; complete lock-up, is typical of most installations.

Similar effects have been observed by recent full scale testing and research conducted at the U. BC in Canada. I made a presentation at the Abu Dhabi Pipeline Transmission Conference discussing the same subject in Sept 2012. We even have one operator here where their pipeline division prefers to usse anchor blocks, but their refinery division does not. Usually the opposite of what is seen in the US and Europe. We will bring up that illogical policy with them very soon.

Independent events are seldomly independent.

 

[Rasoolbc]

Dear BigInch,
Thank you for your advice and thank you for opening a new door in my mind. I will search and read some paper and articles on this topic; however, it would be much appreciated if you provided me with some.

Cheers,
Rasoolbc

 

[Rasoolbc]

Dear BigInch,
I tried to dig US Army Corps Of Engineers publication but I couldn't find anything in "TM 1110". Could you please provide me with more details. They have EM 1110 however, none of their topics are related to "Anchor blocks".
In the meanwhile, I saw a method to replace anchor blocks at each sides of a riser with a beam connecting the s bends together. Could you please refer me to an article, paper or a book if you know any resources?

I appreciate your knowledge sharing in advanced.

Regards,
Rasoolbc

 

[BigInch]

You're right "TM" should be "EM". I think they used to be Technical Manuals, anyway...

http://publications.usace.army.mil/publications/eng-manuals/

scroll down to EM 1110-2

There's not much written about it. Some old Peng articles in the late 70's.
Replacing anchor blocks with flexibility is largely a mater of the exact configuration you have and the amount of movement that you can accept at the connections. Most times it doesn't matter much, unless you have a pump nearby. A typical launcher skid can be placed on a concrete pad without any anchorage bolts, or slotted bolt holes, etc. at least to a certain degree.

You might want to switch to "Pipelines and Fluid Mechanics" forum. I've written a lot about this from time to time. Try a search on that forum.
In the meantime, I've uploaded the old Peng pager for you. That combined with the EM methods will get you a friction values much closer to what is actually observed in the field. The ASCE and American Lifelines method often give values that are only 1/2 the "real" friction values seen in dense sands.





Independent events are seldomly independent.

 

[Rasoolbc]

BigInch,
Thanks and appreciate for sharing your knowledge.

Regards,Rasoolbc