philosophy of B7159

Hi friends
I'm new in stress analysis. So sorry for easy quetions. Why does in BS7159 internal pressure apply force on anchors but in B31.3 doesn't?
And Should I consider this force(forces due to internal pressure) in nozzle design and anchor design?(e.g. If Caesar restraint is value=100KN and Allowable load of the nozzle is 10KN, should I evaluate [100KN-Longitudinal Stress*(FRP area)] for checking with allowable nozzle load?

If you click on 'Special Execution Parameters' and set'activate Bourdon Effects' to 'Translation' you will find an end force due to pressure alone under B31.3 rules.

Of course you must consider this force acting on anchors, restraints and connected equipment.

For a given pressure, FRP will expand axially under pressure much more than steel, due to the filament winding direction, so you should expect some significant numbers.

But in pressure about 20-30 bars for a 30" FRP pipe anchor load due to pressure elongation is so high. How can we overcome to this anchor and nozzle loads?

Ways of overcoming a large axial load in a pipe, due to pressure or anything else are pretty well common to metallic and FRP. Consider changing the route, add flexibility, modify restraints or maybe add an expansion joint.

It is true for long line pipes or pipes according to b31.3.
For pipes according to b31.3 bourdon effect does not active and thus elongation due to pressure doesn't affect on anchor loads. But for example for a 1 meter FRP pipe with 30" diameter and 25bar between 2 anchors, we can't use expansion loop(because pipe is not long enough), neither expansion joint(because of pressure thrust that increases anchors loads). For mentioned example restraints loads due to pressure are about 54tons. What can we do now?

I think you can use EJ. Always nozzles can overcome pressure thrusts due to EJ. AM I right Mr Movez?

Dear Mr Richard Ay,
Are u agree with arian2?

It depends on the system, there is not a definitive "yes" or "no" answer to this question.

Arian2,

I would answer NO to your question about nozzle / EJ thrust. There have been many documented cases where a poorly designed system with an unrestrained EJ has caused failure of connected equipment and / or the pipe in which the EJ was located.

Best advice is ... always beware of forces caused by EJ's and design the entire system accordingly.

Dear MoverZ,

I think pressure thrust acts inside of Eq(with regardless of pressure on annular area of EJ that transfers to nozzle) and baseplate of Eq should overcome to this thrust not the nozzle.
Nozzles of equipment can overcome to internal pressure(thus nozzles can overcome internal pressure of the piping system which connected to them). Consider the nozzle has blind flange, does it fail due to internal pressure? Answer is NO. Because it designed to overcome internal pressure(that is near to piping pressure).

Arian2, I think you are confusing internal pressure with pressure thrust.

Consider a steel pipe system without an EJ, say connecting a vessel directly to a pump with a straight run.

Yes, internal pressure acts on inside of the pump and the vessel wall. But what stops the vessel and pump moving apart dueto those forces ? The pipe of course, which would be in axial tension due to the internal pressure.

Now put an unrestrianed EJ in the pipe and you have no restraint stopping the two nozzles flying apart. That was exactly my point. If you want a stark example of the effects of this, google 'Flixborough incident'. 28 dead I think and an entire plant destroyed by poor use of two unrestrained bellows.

Dear MoverZ,


Mention we are talking about "The Nozzle".
In a "restrained" EJ(an anchor in one side and a nozzle on the other side) the load on "nozzle" is lesser than when we don't have an EJ. For more illustration see the file I have attached(pages 9 and 10).

Arian2,

Above you wrote: "Always nozzles can overcome pressure thrusts due to EJ"

I replied that you are wrong. The diagrams you refer to show what forces act with or without bellows. That's fine, and nice diagrams too by Dr. Becht. However the reaction to those forces, with or without bellows, so far as the equipment is concerned is quite different, as I have explained already.

Look carefully at Dr. Becht's diagrams #9 and #10. Diagram #9 shows an integral piping and no EJ. Diagram #10 with an unrestrained EJ has an anchor added above the bellows. Why ? Because without it, the left side would fly off in the direction ofthe force arrows at the bend. Sorry to repeat myself, Q.E.D.

From discussions above and attached file I may conclude that on nozzle side of EJ baseplate(or legs and foundation) of equipments should overcome pressure thrust(F). And nozzle of the equipments can overcome to F-PA([pressure*annular area of the EJ] that is compressive), as mentioned Arian because this value(F-PA)is lesser than PA(that all nozzle of equipments design for overcome to this load). But another side of EJ should be anchored, as mentioned MoverZ.

I have a basic question friends.
In BS 7159 scope is mentioned that this code is applicable to systems with pressure up to 6 bars for diameter size larger than 600mm.
I don't know Why somebody use this code in higher pressure that is mentioned in code.
Also some softwares just use BS7159 for GRP pipes at any pressure.
Is the scope of code wrong?