Anchor Block sizing 4

[rikz]

Hi All,
Recently in office we had a stern discussion regarding the input for deciding the anchor block design. It was regarding Anchor block sizing (for Saudi Aramco project);and the argument was whether the Anchor block to be designed for Design temperature or operating temperature. the civil department was worried with the high values of forces appearing in there spread sheet when considering the design temperature(230). Hence they were in favor for considering the operating temperature(115 deg F) which is very low considered to design temperature. Please note the buried CS material Gas pipeline complying to ASME B31.8 is , 24 inch size. Please give your most valuable comments......

 

[pennpiper]

The misunderstandings involved in your question have come up on this site (and others) many times in the past. All related but with only slightly different focuses.

What was the source, basis, intent, purpose and relationship of the two Temperatures in this case?
Design Temp. - 230 deg. F
Operating Temp. - 115 deg. F







Sometimes its possible to do all the right things and still get bad results

 

[LittleInch]

Anchor are best designed out by allowing the pipework to move when it comes above ground and / or varying the arrival of the pipeline so it has some buried bends close to the exit point.

What you should be discussing is how to remove the requirement

However if the "system" demands an anchor block, then usual practice as far as I'm concerned is to use max operating temperature versus as laid installed temperature. As PP says, this issue has been discussed many times - do a search. ASME 31.8 in terms of stress analysis uses the terms "operating" temperature and pressure for restrained systems.

Use of "design" temperature is often wildly excessive and normally only advocated by process engineers or those whose financial interests are served by constructing useless and unnecessary huge blocks of concrete (civil contractors in the main).

Often piping engineers get given "free end" movements calculated by a stress analysis of a pipeline which are not the same thing once you actually connect it to some pipework. Once everyone calms down and just builds in a bit of flexibility ( often only 20-30mm movement max) - then the requirement for an anchor block in the first place disappears.

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

 

[BigInch]

The paperwork for the pipeline needs to be consistant with the design temperature and that needs to be set realistically for the pipeline. If it can actually reach 230[°] at the anchor block than that what it needs to be. If it will only see 115, than the design temperature for the pipeline should be redefined at 115.

SaudiAramco loves anchor blocks. ESpecially the ones that you don't need. They never have understood that flexibility is required for pipe design. Ten years ago they were on the right track when they started to consider that anchor blocks would be allowed to move a little bit, but I guess maybe that they forgot that again by now.

230F is reaching a point of no return for anchor blocks. Axial stress doesn't change with wall thickness; only the anchor block load increases when you increase pipe wall. Above 200F the size of the block needed quickly becomes impractical to build, except for the most lucurative budgets. Do they still have money for that?

If you have to stay with the 230F temperature, you may need to allow for 100mm of movement between the pipeline rising above ground and the first above ground pipe support anchor.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[cvg]

I keep this photo of a SA thrust block on my wall for inspiration

Figure 1

http://files.engineering.com/downlo...le=Anchor_block_reduction_-SA_JOT_Q2-2011.pdf

 

[BigInch]

Exactly the article that I was talking about. I thought it was 10 years ago, but that makes me remember it was only 6 years ago. The only thing that works with them is making them think its their idea. YOu can see that they've still got a way to go.

You've got to love those things if you're a contractor .... or a giant parrot.

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[rikz]

Thank you All.....
I am new to this Forum, but the response made me feel at home.....
Really obliged to see your responses,

pennpiper; we still need to understand the basis for this gap in Operating temperature and Design temperature. The Process design was done by a company from USA, Houston.

 

[BigInch]

Gas pipelines used for transportation purposes between plants are usually limited to aftercooler temperatures downstream of a compressor which are usually somewhere around 120F or so. Anything over that is very hot for a "pipeline". Those 200F+ temperatures are reaching the stress limits for buried, fully restrained and rigidly designed pipelines. Expansion loops don't work underground. If the temps don't outright put too much stress on the pipe, which they do, they will at the very least tend to quickly degrade and destroy the pipeline's anticorrosion coatings. This becomes a big problem over 180F and don't think that any coating is guaranteed at over 200F, although some vendors will tell you their stuff works. I wouldn't believe that until it is proven for a number of years more than those coatings have been in marketing. The coatings are still version 1.0 And you also must have enough money to pay for them, which for thousands of meters of pipelines, isn't going to be very practical.

Tmperatures (over 125-130F) usually means the piping is still more associated with a process plant, maybe still above ground and probably not even actually arrived anywhere near a "pipeline". Perhaps this could be piping near a very hot gas well, which in that case the pipe would not be a pipeline, but a well stream "gathering line", which are not usually designed to B31.8

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager

 

[LittleInch]

The problem is that to a process engineer, this strange pipeline thing is simply a short line on his diagram as there are few, if any, process items on it.

Therefore the connecting pipe design temps, which can be 30C or more higher than the max operating temp, just get transferred over.

Also process engineers don't like changing things like design temps in the middle of a line because it blows their mind.....

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

 

[BigInch]

Ya lucky if you even see anything realistic there. They should just stop their diagrams at the plant flange and go into flat-world mode.

That's exactly why I always say "There is no process in pipelines and no pipelines in process."

Find what you like to do, earn a living at it, and then make your lifestyle fit your income. — Chuck Yeager