TEMA Standard for Tube Vibration

TEMA STANDARDS Section.5

RCB-4.56 TUBE BUNDLE VIBRATION
Shell side flow may produce excitation forces which result in destructive tube vibrations. Existing predictive correlations are inadequate to insure that any given design will be free of such damage. The vulnerability of an exchanger to flow induced vibration depends on the flow rate, tube and baffle materials, unsupported tube spans, tube field layout, shell diameter, and inlet/outlet configuration. Section 6 of these Standards contains information which is intended to alert the designer to potential vibration problem. In any case, and consistent with Paragraph G-5, the manufacturer is not responsible or liable for any direct, indirect, or consequential damages resulting from vibration.

RCB-4.6 IMPINGEMENT BAFFLES AND EROSION PROTECTION
The following paragraphs provide limitations to prevent or minimize erosion of tube bundle components at the entrance and exit areas. These limitations have no correlation to tube vibration and the designer should refer to Section 6 for information regarding this phenomenon.

RCB-4.61 SHELL SIDE IMPINGEMENT PROTECTION REQUIREMENTS
An impingement plate, or other means to protect the tube bundle against impinging fluids, shall be provided when entrance line values of ρV2 exceed the following: non-abrasive, single phase fluids, 1,500(2,232); all other liquids, including a liquid at its boiling point, 500(744). For all other gases and vapors including all nominally saturated vapors, and for liquid vapor mixtures, impingement protection is required. V is the linear velocity of the fluid in feet per second (meters per second) and ρ is its density in pounds per cubic foot (kilograms per cubic meter). A properly designed diffuser may be used to reduce line velocities at shell entrance.

RCB-4.62 SHELL OR BUNDLE ENTRANCE AND EXIT AREAS
In no case shall the shell or bundle entrance or exit area produce a value of ρV2 in excess of 4,000(5,953) where V is the linear velocity of the fluid in feet per second (meters per second) and ρ is its density in pounds per cubic foot (kilograms per cubic meter).

RCB-4.621 SHELL ENTRANCE OR EXIT AREA WITH IMPINGEMENT PLATE
When an impingement plate is provided, the flow area shall be considered the unrestricted area between the inside diameter of the shell at the nozzle and the face of the impingement plate.

RCB-4.622 SHELL ENTRANCE OR EXIT AREA WITHOUT IMPINGEMENT PLATE
For determining the area available for flow at the entrance or exit of the shell where there is no impingement plate, the flow area between the tubes within the projection of the nozzle bore and the actual unrestricted radial flow area from under the nozzle or dome measured between the tube bundle and shell inside diameter may be considered.

RCB-4.623 BUNDLE ENTRANCE OR EXIT AREA WITH IMPINGEMENT PLATE
When an impingement plate is provided under a nozzle, the flow area shall be the unrestricted area between the tubes within the compartments between baffles and or tube sheet.

RCB-4.624 BUNDLE ENTRANCE OR EXIT AREA WITHOUT IMPINGEMENT PLATE
For determining the area available for flow at the entrance or exit of the tube bundle where there is no impingement plate, the flow area between the tubes within the compartments between baffles and/or tube sheet may be considered.

RCB-4.63 TUBE SIDE
Consideration shall be given to the need for special devices to prevent erosion of the tube ends under the following conditions:

(1)  Use of an axial inlet nozzle.

(2)  Liquid ρV2 is in excess of 6,000(8,928), where V is the linear velocity in feet per second (meters per second), and ρ is its density in pounds per cubic foot (kilograms per cubic meter).

TEMA STANDARDS Section.6

V-1 SCOPE AND GENERAL
V-1.1 SCOPE
Fluid flow, inter-related with heat exchanger geometry, can cause heat exchanger tubes to vibrate. This phenomenon is highly complex and the present state-of-the-art is such that the solution to this problem is difficult to define. This section defines the basic data which should be considered when evaluating potential flow induced vibration problems are requested to be evaluated, the relationships presented in this section and/or other methods may be used. Due to the complexity of the problem, the TEMA guarantee does not cover vibration damage.

V-1.2 GENARAL
Damaging tube vibration can occur under certain conditions of shell side flow relative to baffle configuration and unsupported tube span. The maximum unsupported tube spans in Table RCB-4.52 do not consider potential flow induced vibration problems. In those cases, where the analysis indicates the probability of destructive vibration, the user should refer to Paragraph V-13.

V-2 VIBRATION PATTERNS
Mechanical failure of tubes resulting from flow induced vibration may occur in various forms. Damage can result from any of the following independent conditions, or combinations thereof.

V-2.1 COLLISION DAMAGE
Impact of the tubes against each other or against the vessel wall, due to large amplitudes of the vibrating tube, can result in failure. The impacted area of the tube develops the characteristic, flattened, boat shape spot, generally at the mid-span of the unsupported length. The tube wall eventually wears thin, causing failure.

V-2.2 BAFFLE DAMAGE
Baffle tube holes require a manufacturing clearance (see Paragraph RCB-4.2) over the tube outer diameter to facilitate fabrication. When large fluid forces are present, the tube can impact the baffle hole causing thinning of the tube wall in a circumferential, uneven manner, usually the width of the baffle thickness. Continuous tinning over a period of time results in tube failure.

V-2.3 TUBESHEET CLAMPING EFFECT
Tubes may be expanded into the tube sheet to minimize the crevice between the outer tube wall and the tube sheet hole. The natural frequency of the tube span adjacent to the tube sheet is increased by the clamping effect. However, the stresses due to any lateral deflection of the tube are also maximum at the location where the tube emerges from the tube sheet, contributing to possible tube breakage.

V-2.4 MATERIAL DEFECT PROPAGATION
Designs which were determined to be free of harmful vibrations will contain tubes that vibrate with very small amplitude due to the baffle tube hole clearances and the flexibility of the tube span. Such low level stress fluctuations are harmless in homogeneous material. Flaws contained within the material and strategically oriented with respect to the stress field, can readily propagate and actuate tube failure. Corrosion and erosion can add to such failure mechanisms.

V-2.5 ACOUSTIC VIBRATION
Acoustic resonance is due to gas column oscillation and is excited by phased vortex shedding. The oscillation creates an acoustic vibration of a standing wave type. The generated sound wave will not affect the tube bundle unless the acoustic resonant frequency approaches the tube natural frequency, although the heat exchanger shall and the attached piping may vibrate, accompanied with loud noise. When the acoustic resonant frequency approaches the tube natural frequency, any tendancy toward tube vibration will be accentuated with possible tube failure.