EJMA

For the bellow to effectively work the following design considerations shall apply to the Piping System that employs a bellow.

• The design of the piping system employing a bellow shall take into account the recommendations made by EJMA Standard.

• The specification for the Bellow shall as a minimum provide technical information as per Specification Sheet given as Appendix-A of EJMA.

• The type of the bellow shall be selected depending on the magnitude of the thermal movement of the connected piping and the configuration of the piping profile in relation to the location of the Bellow.

• In general, caution shall be exercised in employing a bellow in a piping system operating under cyclic loading condition (e. g. due to temperature cycle). If no solution is available as an alternative to bellow then the number of temperature cycles anticipated during the design life of the system shall clearly be indicated in the Bellow Specification for the vendor to confirm the fatigue life expectancy.

 Under normal circumstances stress relieving or annealing shall not be specified for the bellow since the life of a bellow greatly relies on its improved fatigue strength due work hardening of austenitic stainless steel during the forming operation of the convolutes.

• The supporting of the piping system employing a bellow shall be such that the movement of the connected piping at the bellow ends is positively predictable. The support shall be adequately designed for the highest pressure either during operation or hydro test condition.

• The bellow shall not be subjected to torsional Rotation.

• The bellow material shall be compatible with the flowing medium. Specific consideration shall be given to the following.

• Series 300 stainless steel against chloride stress corrosion.

• Nickel alloys against caustic induced stress corrosion.

• Nickel alloys against presence of sulphur.

• Compatibility of bellow material against pipeline cleaning chemicals if they are dozed in the piping system on regular intervals.

• Leaching of the bellow material from the insulation material.

• Requirement of internal sleeves shall be specified in an application involving fluid velocities which can induce resonant vibrations. The evaluation of acceptable flow velocity limits (based on EJMA, Section C-3) is covered in section (internal sleeve requirement) of this chapter. The sleeves are normally installed in the direction of flow.

However in case back flow is anticipated during operation the same shall then be highlighted clearly in the specification to allow the bellow manufacturer to provide extra heavy sleeve and thereby preventing a possible damage of the bellow resulting from the buckling of the sleeve.

• The Design Pressure of the bellow shall be based on the actual maximum working pressure of the pipeline under question. No ad-hoc cushion shall be allowed in specifying the design pressure.

• The Hydraulic test pressure of the bellow shall be 1.5 times the design pressure (1.1 times in case of pneumatic test pressure) with due allowance for temperature correction factor. However the Test Pressure calculated in the above manner must not produce membrane stresses in excess of Yield Strength at room temperature.

• The maximum, minimum and installation temperature shall be specified accurately and a suitable pre-compression of the bellow shall be considered and specified accordingly if ambient temperatures may vary significantly during pipeline construction.

 The Insulation Guard Sleeve shall be specified in case of insulated Bellows.

• The displacements to be absorbed by the bellow shall be based on the expected piping growth including the terminal movements. In addition to the above the specified displacements shall also account for the following eventualities

• The actual metal temperature of the piping may not necessarily attain the design temperature used for calculation of the expected thermal growth of the piping.

• The installed location of the piping supports (e.g. guides/ anchors etc.) in the field may not necessarily be exactly in accordance with the design.

• The temperature range attained during actual operation cycle may not necessarily be exactly same as anticipated in the design.

• The bellows when handling process fluids which can solidify or scale to pack the convolutions shall be provided with necessary means to avoid the same. Use of internal sleeve, purge connections (for gas/ vapour mediums) and drip hole (for trapped liquid) are some of the ways to achieve the same.

 Depending on the severity of the process/ design condition the bellow may be specified with extra safety features as below:

• Extra heavy external cover which would impede the effect of the jet/ splash of escaping fluid in case of a bellow failure.

• Limit rods employed from the consideration of dynamic loading can be designed for restraining the pressure thrust in case of an anchor failure.

• A two-ply or concentric double shell Bellow with both the ply’s capable of withstanding the full line pressure.

• It is normally a good practice to provide a sketch of the piping system with details of all supports and other design data as part of the bellow specification for establishing a clear understanding with the bellow manufacturer.

• The supports on a piping system employing a bellow shall have clear space around the supports to allow access for their inspection during hydro test and during plant operation.