Universal expansion joints
Fully articulated expansion joints are mostly employed in short pipe-linkages where thrusts generally spring up outwards all together causing expansions towards all directions.
These joints performance cover a wide field of action and i.e.: in place of axial joints when they cannot be used owing to the thrust generated by internal pressure;- like dampers able to counterbalance mechanical vibrations arising near pumps or compressors.
When mechanical vibrations take place in all of the three orthogonal planes we have to apply to a couple-joints-system and that is to say: a device formed by one universal joint plus one angular joint assembled together with an angle of 90° each other.
Of course the above mentioned compensation system must be placed quite near the vibrating machinery in order to reduce the volume of the involved masses.
To complete pipe plant, an anchor point must be installed just afterwards the side where pipeline last joint has been placed.
Unfortunately there is a limit on dampers performing and this is due to the highest frequency vibrations caused by turbulent fluids near desuperheater, reduction valves, or when vibrations are not to impute to the machinery but to the high speed of fluids.
Pipe guiding
Strong slides are not strictly necessary provided that: 1st) a suitable side clearance in the last section of pipe just near flexible joints be planned for slides.
As a matter of fact said clearance will enable slides to absorb the value of stresses in connection with the arch height; 2nd) frictional forces generated by slides be of no account. A good sliding of slides is necessary to ensure regular and constant movement to pipeline in order to avoid dangerous expansion stoppings.
As above must be carefully arranged in advance otherwise pipeline after having overcome the obstacles that obstructed its normal expansion, would suddenly expand in a violent way with thrusts and dangerous shakings.
Anchor points
Contrarily to what happens to axial joints for which anchor points have to be very strong, in this case anchor devices are only submitted to the little bellows flexibility of the expansion joint in action and to the sum of the slides frictionals forces.
As already said before, thrusts generated by pressure are absorbed by rods.
Technical data