Dear senior engineers
I have modeled a SS buried pipe.
I cant put Anchor block as per civil department comment for intersection points.
So I have too many overstressed points!!!
What should I do?
Best Regards

I am also facing the same problem, using API 5L X-60
I have previously done a model with similar conditions but this time a bit longer buried pipe is showing overstressed points.

Guys i am also waiting for the Reply anxiously.

As usual here, I recommend that you have your analysis reviewed by a more senior engineer, if possible, to make sure you've done it correctly.

In general, if you have a buried butt-welded pipe (as I would expect from the SS or API 5L X-60 material notes), and you've done the model correctly, you should have no great problems with stresses. You may well be using far too high of a design temperature for your piping - once it goes underground, the fluid contents are going to assume the temperature of the surrounding soil rather quickly unless you have insulated the line. And, if you have insulated the line, how have you modeled the structural effect of the insulation?

There should be no need for thrust blocks in a butt-welded system. They are there in mechanical joint systems to prevent the joints from pulling apart. This is obviously not an issue for butt-welded piping.

I don't do a lot of underground pipe analysis, and so have always found that using the UG modeler after a long time away is very foreign. Usually, the crew at COADE can walk me through my senior moments - probably they can help you with filling in the blanks too.

I am not sure either of you has provided enough information for me to give a better answer.

I don't know the detail of your study,
check why these anchor blocks are required.
Usually anchor blocks are required in a long pipeline, they could be either buried or A/G. the purpose is to protect, A/G piping avoid loads from the expansion movement of long pipelines.
Another application is fire water system when it s buried, using non metallic pipe ( ie HDPE,)thrust block are required in the change of direction ( elbows at the ends of large buried loop).
However, you shouldn't have overstress, check you have properly modeled your system ( soil parameters are very important).
Regards,
Yani

enclosed pls find the job
regards

i have also shared a file, kindly check it and tell me where i am going wrong . Its a small model and showing stresses at its extreme bends

I worked on a number of buried models for district cooling networks, I usually get high stresses at tee junctions, even though, I will be specifying a 3 weld type tee, what I normally do is delete the K values that CAESAR specifies in the soil restrains for that failing node. Our pipes are carbon steel with 100mm Polyurethane and an HDPE insulation Jacket.

Yes, removing soil restraint will add flexibility and reduce stress due to strain.

But... does your model still reflect actual field service?

Dave,
How accurately do the soil restraints represent the actual forces acting on the bends and tees?
In my case all of my tees are carbon steel API 5LB, 3 weld type or weldolets, as I mentioned earlier all fittings are pre-insulated with 100mm Polyurethane and an HDPE Jacket.
Also my understanding is that when I delete the K value from the Bi-linear soil restraints I will be removing flexibility from around the fitting, infect the shape of the restraint will change from the spring like shape aero to the rigid type shape.
Thanks for your input Dave.

Oh...
So you have left the restraint in the model but you removed the stiffness entry?
Then, yes, you have increased the stiffness at that restraint to what we call "rigid".

How accurate are the calculated loads? Hard to say. Certainly not more accurate than your soil parameters.

How "flexible" is that 100mm of polyurethane in relation to your soil? Consider your strain loads being distributed based on the bending stiffness of the pipe, the bearing stiffness of the soil and the stiffness of the insulation.

sir,

i have a 4" line which has 430 mtrs straight run, which is buried,but i wanted to know ,what are the load cases to be cosidered in it for fault less analysis? and whether their is any requirement of giving thrust blocks if yes then how to give them ...........

are thrust block indicate axial stops in the pipe.

please answer the above quary urgent!!!!!

D paul

On this forum and others there are two kinds of questions.

Type A - Questions that DO NOT relate to a real situation. The subject is general, non-specific or hypothetical. This type of question does not require specific information and only expects a non-specific (Type A) answer.

Type B - Questions that DO relate to a real situation. The subject is very specific.
This type of question should be accompanied by the complete slate of details on which to base the very specific (Type B) answer.

In many cases the person who submits a Type A question ends up rejecting the Type A answer and pushes for a full Type B answer.

In even more cases a person submits, what they intend to be a Type B question but furnish no detail information. They are then upset when they only get a Type A answer.

deb j paul, you have submitted a question and stated that it is a real problem. Therefore it is a Type B question. However you have not provided any information for us to base our answer. We can only give a general answer.

If you want a specific answer to this (or any other) question I suggest you provide information such as:
- Pipe Material
- Pipe wall schedule
- Commodity
- Operating temp
- Depth of cover
- Type of soil
- State, Country of installation
- Piping Code
- DOT jurisdiction
- Etc.

Jop (aka Pennpiper)

Dave Diehl,

Suppose you have a 30" dia. long line (40 miles) which has been buried for ten or fifteen years. You dig it out and cut it. It seems to me that the cut end will move clear until you reach the virtual anchor. Should you make your tie-in on a cold day the pipe will overstress on hot days or when hot fluid is transported will it not? Can this be modeled with CAESAR II?

Regards,

KK

I would imagine that the line would be back at ambient condtions when you uncover it and cut it. If that's the case, I would expect the pipe to be right where I laid it down in the first place.
If there was any plastic response of the piping system since it was buried, then I might expect that point to have a new equilibrium position. But that's easier to talk about than it is to quantify in your CAESAR II model.
But if you are still in elastic response, then your tie in point would shift based on the difference between the loads that were on the system when it was buried and the loads on the system today. You could estimate the "new" position of your tie-in point by including some net temperature change (cut and lay pipe on a hot summer afternoon and tap in to it on a cold winter day) or some support settlement. And yes, there is a possibility that when your new piping subsystem goes into operation or the entire system is unloaded, new strains will be introduced and the overall system might fail. I believe you can find more about this subject on this forum by searching "hot tap".