Anti-Vibration Technologies for Heat Exchangers

NPRA Maintenance and Reliability Conference May 26, 2011

Amar S. Wanni Jerard T. Smith Zdenka F. Ruzek

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Outline

Flow-Induced Vibration Problems in Heat Exchangers Including Examples of Failures

Overview of Vibration Analysis

Example Anti-Vibration Solutions for Heat Exchangers

Analysis of Vibration with HTRI Xvib

Questions / Discussion

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The Flow-Induced Vibration Problem In Heat Exchangers: Background

Tube damage from flow-induced vibrations has increased over the past 5 to 10 years, primarily from two main sources: Advances in catalyst and control technologies allow

operators to increase plant capacity by simply increasing flow through existing process equipment

New exchanger designs are smaller than in the past, which entails greater shell side velocities

Tube failures are always very expensive and lead to lost production, contaminated products, additional energy usage, and/or high repair costs

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Most Likely Cause for Tube Vibration Damage: Fluidelastic Instability When Local Velocity Exceeds Critical Velocity, Tubes Experience

Orbital Motion that Could Lead to Necking at Baffle Holes HTRI Programs (Xist and Xvib) Predict Fluidelastic Instability Ratio

(FIR = Local Velocity/Critical Velocity) FIR Must be Kept Below 0.8 for high-quality Design Rate of Tube Failure Proportional to FIR4 if FIR > 1

Vortex Shedding Could Lead to Tube-to-Tube Collisions, and Failure at Baffles, Near Tubesheet, and U-Bend Regions Vortex Shedding Frequency Ratio Preferably Kept Below 0.8 Limit Cross-Flow Amplitudes to Less Than 10% of Tube Spacing

The Flow-Induced Vibration Problem In Heat Exchangers: Background (continued)

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Acoustic Vibration Not Known to Have Caused Tube Failures

Often, Flow-Induced Vibration (FIV) Conditions are Misdiagnosed

Often, Plant Operations Do Not Facilitate Proper Root Cause Failure Analyses

Leaky Tubes are Plugged and Exchanger Quickly Put Back in Operation to Avoid Throughput Losses

Photographs of Failed Tubes are often Unavailable

The Flow-Induced Vibration Problem In Heat Exchangers: Background (continued)

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Examples of Tube Failures in Field

Feed/Effluent Exchanger Tube Damage Shellside : Reactor Effluent Failure Mode: Vortex Shedding

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Examples of Tube Failures in Field (Continued)

Liquid on Shellside Failure Mode: Fluidelastic Instability

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Examples of Tube Failures in Field (Continued)

Gas on Shellside Tube Fretting at Baffle Hole

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Anti-Vibration Solutions for Heat Exchangers

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Needs for Anti-Vibration Technologies

Improve reliability of existing equipment that may have already suffered vibration damage

Provide tube vibration mitigation to an existing bundle predicted to have vibration problems at a future/planned increased throughput

Modify baffle design to decrease shellside pressure drop while also providing vibration mitigation

Design new exchangers with axial shell side flow to substantially decrease pressure drop (e.g., compressor circuits)

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Anti-Vibration Technologies Open Substantial Opportunities

In Existing Bundles Allow greater flow rates while minimizing risk of vibration

damage Allow re-use of bundles that failed due to flow-induced vibration

damage of tubes

In New Bundles... Allow use of fewer baffles (e.g., 50% Less) decreasing shellside

p by as much as 75% Allow design of exchangers with axial shellside flow providing

smaller footprint, lower cost, and superior performance than other technologies available in todays market

Allow design of heat exchangers at their optimum configuration based on heat transfer and pressure drop considerations.

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ExxonMobil has Developed a Suite of New Anti-Vibration Technologies:

Dimpled Tube Support (DTS)

Saddled Tube Support (STS)

Slotted Baffle Exchangers (SBX)

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Dimpled Tube Support (DTS)

Each strip is fabricated from a thin strip of metal

Outer end consists of a dimpled region Dimples lock into tubes avoiding

accidental dislodging Remainder of strip has corrugations

somewhat similar to dimpled region Both dimpled and corrugated regions

deflect tubes slightly thereby stiffening tubes and avoiding tube chatter

Suitable for all tube layouts (30, 45, 60, and 90)

Suitable for vertical tube bundles Modified DTS strip used as a U-Bend

stiffener Applicable even when some of the

tubes are warped 13

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Dimpled Tube Supports - Installation

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Saddled Tube Supports (STS)

Each support is formed by welding of two strips that are fabricated to provide Saddles

A locking device prevents accidental dislodging of tube support

Similar to DTS strips, each tube is slightly deflected to stiffen tubes and provide vibration mitigation

Suitable for 45 and 90 tube layouts only

Suitable for low-finned tubes made of softer metals such as carbon steel and brass

Suitable for exchangers with axial shell side flow

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Saddled Tube Supports - Installation

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DTS and STS Strip Concept

DTS and STS strips are used to mitigate vibrations perpendicular to the tube axis

Inserting strips into every other tube lane diminishes

tube chatter as the tubes are slightly deformed and pushed against the baffle holes - Tube-to-baffle impacts reduced - Natural frequency of the tubes is substantially

increased with a negligible rise in shellside pressure drop

The tube bundle as a whole tightens up and will act as one rigid entity, significantly lessening relative motion of components

Anti-Vibration Technologies for Heat Exchangers

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EXAMPLES DTD / STS

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Repair of Failed Heat Exchangers (Example 1) An LNG Plant experienced tube failures in a

number of kettle reboilers Vibration analyses showed a very high

probability for tube damage due to fluidelastic instability as well as excessive cross-flow amplitudes due to vortex shedding

A field inspection showed heavy fretting at tube support locations in top 10 tube rows

Unsupported tube span was around 4.5 ft for tubes having a diameter of 0.75 in and a wall thickness of 0.065 in

DTS strips inserted at 1/3 and 2/3 locations within each unsupported span

Free movement of tubes non-existent following DTS installation; no further vibration failures reported

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Kettle Reboiler

Original Conditions

Conditions with DTS

Duty (MBtu/hr) 244 244

P (psi) 0.29 0.29 Fluidelastic Instability Ratio (FIR)

4.1 0.2

Vibration Problems YES NO

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Application of DTS Retrofit into Treat Gas Heater (Example 2)

Current Case has no vibration problems

Future operating case with 30% increase in capacity predicted to have vibration problems

Use of DTS allowed re-use of existing equipment while eliminating vibration potential

A new design would have required replacement of both shell and bundle and potentially piping modifications

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Feed / Effluent Heat

Exchanger

TEMA BEU 33 x 126, 1 tubes 1,180 ft2 Segmented baffles

Existing Design

Conditions

30% Capacity

Creep without DTS

30% Capacity

Creep with DTS

Duty (MBtu/hr) 49.4 64.2 64.2

p (psi) 8.4 10.0 10.2 Vibration Problems NO YES NO

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An Optimum Design (Example 3)

Optimum conventional design even with double-segmental baffles has vibration problems

Alternate conventional design to avoid vibration requires a larger shell diameter (44 in vs. 36 in)

Alternate exchanger also requires No-Tube-In-Window (NTIW) design

Optimum Design with DTS: No vibration problem

Smaller shell diameter

Lower shell side pressure drop 1.4 psi vs. 1.8 psi

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Condensing Service

Exchanger

Conventional Design

(with no vibration)

Optimum Design with DTS

TEMA: AES

44 x 192

Plain Tubes NTIW/Seg

2p / 1s

36 x 192

Plain Tubes Double seg

2p / 1s

Duty (MBtu/hr) 17.7 17.7

p (psi)

1.8 1.4

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October 20, 2011

Application of SBX to Debottleneck Gas Loop (Example 4)

Original Bundle with Conventional Baffles Experienced a Shellside Pressure Drop of 110 kPa

SBX Bundle Designed for 24 kPa Axial Shellside Flow Decreases

Shellside Heat-Transfer Coefficient

To Maintain Heat Duty, Low-Finned Tubes Were Used

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Exchanger: TEMA AEU

Feed Preheat w/ Steam

Original bundle (at debottleneck

conditions) SBX Bundle

25"x126" Shell

1200 ft2 0.75 plain

tubes Segmental

baffles

2140 ft2 0.75 finned

tubes No baffles (axial

flow)

Duty (MBtu/hr) 97.6 103

p(psi) 16 3.5 Vibration Problem? Yes No

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Example of DTS Installation

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Example of DTS Installation in U-Bend

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Example of DTS Installation

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HTRI Xvib DTS/STS Modeling Options

Capability to simulate shell and tube heat exchanger with specific locations of DTS or STS and their effect on flow induced vibration probability

Capability to model DTS and STS as tube supports to reduce unsupported tube span to affect flow induced vibration however without impacting pressure drop or flow velocity

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Anti-Vibration Technologies for Heat Exchangers

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HTRI Xvib

Anti-Vibration Technologies for Heat Exchangers

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SAMPLE CASE DETAILS

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Anti-Vibration Technologies for Heat Exchangers

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QUESTIONS AND DISCUSSION

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In Conclusion

AVTs technology will eliminate tube chatter Suitable for U-bend and vertical bundles Applicable even when some of the tubes are

warped HTRI software (Xvib) now includes DTS

and STS modeling options Licensed to a select number of qualified

heat exchanger manufacturers for applications worldwide

Successfully used at ExxonMobil and third party sites

ExxonMobil Research and Engineering Company proprietary technology

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Anti-Vibration Technologiesfor Heat ExchangersOutlineThe Flow-Induced Vibration Problem In Heat Exchangers: BackgroundThe Flow-Induced Vibration Problem In Heat Exchangers: Background (continued)Slide Number 5Examples of Tube Failures in FieldExamples of Tube Failures in Field (Continued)Examples of Tube Failures in Field (Continued)Anti-Vibration Solutions for Heat ExchangersNeeds for Anti-Vibration TechnologiesAnti-Vibration Technologies Open Substantial OpportunitiesExxonMobil has Developed a Suite of New Anti-Vibration Technologies:Dimpled Tube Support (DTS)Dimpled Tube Supports - InstallationSaddled Tube Supports (STS)Saddled Tube Supports - InstallationDTS and STS Strip ConceptEXAMPLES DTD / STSRepair of Failed Heat Exchangers(Example 1)Application of DTS Retrofit into Treat Gas Heater (Example 2)An Optimum Design(Example 3)Application of SBX to Debottleneck Gas Loop (Example 4)Example of DTS InstallationExample of DTS Installation in U-BendExample of DTS InstallationHTRI Xvib DTS/STS Modeling OptionsHTRI XvibSAMPLE CASE DETAILSQUESTIONS AND DISCUSSIONIn Conclusion