EXPANSION JOINTS

[gorkus]

HELLO,

AT WHAT DISTANCE SHOULD EXPANSION JOINTS BE PLACED FROM THE PUMP IN A PIPING SYSTEM ??.

IS THERE ANY STANDARD ABOUT IT.??


THANKS IN ADVANCE


GORKUS

 

[pennpiper]

As far away as possible. Maybe on the shelf in the Expansion Joint vendors warehouse would be a good place.

The point I am trying to make is this, design the pump piping so there is NO expansion joint. They are not reliable, prone to fatigue failure and thus cause loss of production and possible injure to operators and maintenance workers.

 

[nickelkid]

pennpiper is right, but if you must...

http://ejma.org/EJMAStandards.htm

 

[JohnBreen]

There is NO STANDARD (excuse my shouting) regarding the proximity of EJ's to pumps.

There are many things that must be considered when you employ EJ's. Pressure thrust is one of the most important considerations. Also you MUST follow EJMA standards regarding the placement of guides and other restraints. Every piping system is different (geometry, pipe size and schedule, etc.) so there are no "rules of thumb" to be applied. If you have room to use expansion loops (and guides and line stops) that should be your first choice.

 

[chief]

There is no reason not to use expansion joints, provided you are not pumping a hazardous fluid. They are ideal for preventing pipework induced stresses/misalignments and vibrations from damaging pump casings. Invaluable in areas where there are seismic vibrations expected and unstable decking, such as marine ships/rig environments etc.Ensure the joints are composed of the correct material for the fluid medium.
Ideal position is directly coupled at suction and discharge of pumps.
Lifecycle expectancy can be ascertained by experience and a change out schedule put in place to prevent unscheduled failure.

Offshore Engineering&Design

 

[C2it]

There are many reasons to avoid expansion joints, notably unreliability, susceptability to damage, required maintenance and inspection. They do have their place, but in most cases pipe flexibility is the better solution. Loops and properly considered use of natural pipe flexibility does not require servicing, change-out schedule or (usually), lifecycle prediction.

If bellows were as reliable as pipe, double ply with pressure monitoring would not exist.

 

[PaulDBerg]

Yow. Such strong feelings about not using exp joints. Funny line, though, penniper.

The first point is the question was really about flexible pump connectors. Expansion joints are a subset of that group. That is, those flexible connectors that compress. Braided metal hose type flexible connectors, for example, are popular pump flexible connectors that do not compress.

Second, almost always the thing that screws you up is not accounting for the thrust load that you get with true expansion joints. If you don't understand that concept, you will need to learn.

Finally, as for the distance, they are usually attached directly to the pump.

(Full disclosure: I work for Flexicraft...)

 

[Artisi]

The question was about expansion joints NOT flexible connectors.

Remember the thrust generated by an unconstrained expansion joint is the pressure x the actual internal area of the expansion joint. This can be an enormous thrust into a pump casing - ever enough to push it off the base plate.

I agree with pennpiper - in the store is a good place for them, although my comments are based on the above which is additional to pennpiper.

 

[PaulDBerg]

There are ways to handle the thrust load with pumps:

- for a braided metal flexible connector, the braid takes the load, so you don't have to worry about it.

- for rubber joints, you can add "control units", which flange into place during installation, and have rods to take the load.

- with metal bellows joints, you can buy with tie rods.

The downside to these remidies is that there can be no axial movement. Only lateral and angular. But this is OK if you are concerned about slight misalignment and vibration isolation.

If axial movement is needed because of thermal growth, and so you want to use a joint with no control units or tie rods, the thrust load (and other loads) should be lower than the allowable pump nozzle loads.

 

[Artisi]

PaulBerg

No argument with your comments re controlling axial thrust -the problem is that you and I understand the way round it but the majority of people installing expansion joints don't know and most if not all manufactureres / supplier forget to tell the end users about the thrust involved.

 

[gerhardl]

Gentlemen, please...!

Using any piping component wrong or outside the general allowed specification, will create a possibillity of failure and injury, and if this is the general way of doing things, it would be best to sit completely still and not build anything at all including pumps and pipelines.. ;-).....

OK, my point is that I have seen more problems with pipelines, including missing ways of easy mounting or dismounting of valves and other components, not using expansion joints where they should have been, than by wrongly used expansion joints.

This includes both lockable (dismantling joints) and not lockabel (expansion / dismantling joints).

Expansion joints are robust and solid pipeline components, and correctly selected by type and dimension, they can be placed almost anywhere in a pipeline construction, if correctly mounted and pipeline correctly supported.