Acoustic Induced Vibration (AIV)

September 28, 2018

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What is AIV?

Acoustic Induced Vibration (AIV) refers to structural vibration in a piping system with vapor flow excited by intense acoustic pressure. AIV is caused by acoustic energy from pressure reducing devices with high-pressure drops and vapor services mass flows. High-frequency sound waves can excite the circumferential-mode of vibration of pipe and may result in fatigue failure at welded attachments where stress concentration occurs.

  • Stress Category: Primary Stress
  • Stress Type: Hoop/Circumferential Stress
  • Frequency: 500-2500 Hz
  • Design Life: Millions of cycles
  • Failure Locations: Happens at peak stress (discontinuity) where we have high-stress concentrations

Circumferential “Shell” Mode of Vibration

High Frequency Vibration Courtesy Of Energy Institute Guideline Low Frequency Vibration Courtesy Of Energy Institute Guideline
High-frequency vibration courtesy of energy institute guideline Low-frequency vibration courtesy of energy institute guideline

Why is AIV more important than years ago?

  • Larger pipes and higher D/T ratios
  • High-pressure drops and flow rates (higher plant output)
  • Use of thinner pipe wall thickness (cost savings)
  • Use of cheaper piping components (cost savings)

Typical Sources of AIV

  • Relief valves
  • PSV bypass valves
  • Control valves
  • Blow-down valves
  • Manual vents
  • Compressor recycle valves

AIV High-Frequency Circumferential Shell Modes from Finite Element Analysis

Aiv High Frequency Circumferential Shell Modes From Finite Element Analysis

Piping Technology & Products can perform numerous types of AIV analyses for a variety of applications and projects.

 

Acoustic Induced Vibration Hold Down Support Design and Testing

PT&P custom designed a heavy-duty hold-down pipe clamp and stanchion to accommodate the acoustic induced vibrations on the flare line at an LNG plant. Extensive Finite Element Analysis was run on multiple (30) designs. Once satisfied, engineers approved the fabrication of our design.

Aiv Hold Down Ansys
AIV Hold Down ANSYS

The customer was able to restrain the acoustic induced vibration on the flare line and start the LNG plant. This plant is now shipping gas around the globe.

 

AIV (Acoustic Induced Vibration) Supports Supplied in conjunction with active LNG Releases

PT&P earned a “Superior” rating by meeting the project’s AIV requirements while maintaining the current lead times for the cold shoes, engineered supports, standard supports, and instrument stands.

Aiv (Acoustic Induced Vibration) Supports Supplied In Conjunction With Active Lng Releases Aiv (Acoustic Induced Vibration) Supports Supplied In Conjunction With Active Lng Releases

The customer was able to retrofit installed cryogenic pipe supports with reinforcement pads to accommodate additional stresses caused by unanticipated acoustic vibration. Lead times were set and PT&P beat the scheduled module “sail” dates.

Load Testing

November 30, 2017

The Objective

The objective of the load test is to determine the maximum load for pipe supports and other products.

What We Do

To determine the failure loads, PT&P’s engineers and quality control crew will specify goals for the test such as measuring the axial load, lateral load, vertical tension and temperature.

After Completion

Once the test is completed, the engineers will discuss the data reported and propose alternatives that will improve the amount of force the product will withstand.

Bob TestingLateral-load testing of a 30″ dia. pre-insulated shoe at cryogenic condition

Bob Test1Axial-load testing of pre-insulated shoes at cryogenic condition

Testing ReaderThermocouple used in load testing

Randy TestingClient and PT&P engineers witnessing results of Axial-load test under design condition

For further information, please submit your inquiries via via the online inquiry form or contact us at info@pipingtech.com

Snubber Testing

PT&P has two test machines specifically designed for testing snubbers for piping applications, one for routine testing of hydraulic snubbers, and a more sophisticated machine that can perform a wide range of tests on both hydraulic and mechanical snubbers.

PT&P STADAS Snubber Test Machine

The STADAS is a trailer mounted snubber test machine manufactured by Paul-Munroe Inc., California. This computer controlled, hydraulic test machine is used to test the performance of mechanical and hydraulic snubbers ranging in size from 150 lb. to 135,000 lb. The STADAS may also be used to verify snubber conditions at the point of manufacture, or during an outage (refueling) at the plant site.

The STADAS machine is capable of controlling a test, following any load sequence needed. It can then plot the test results immediately, and save the results to disk for future reference.

The main frame of the STADAS machine is comprised of two drive cylinders, which supports the snubber being tested. The smaller drive cylinder is used for snubbers rated to 6000 lb., and the larger drive cylinder is used for snubbers rated up to 150,000 lb. Each drive cylinder is equipped with an electro-hydraulic servo-valve, load cell and connections to the hydraulic system.

The Hydraulic Snubber Test Machine is mainly used to perform testing for hydraulic snubbers, it has a similar test bed like the STADAS machine, however, it is not computer controlled. It is adequate to perform all the tests normally required for hydraulic snubbers, such as quality control and periodic tests that are sometimes required as part of plant maintenance programs. Mechanical snubbers can also be tested on this machine, but due to the complication of the process, mechanical snubbers testing is usually performed on the STADAS machine.

The Objective

The objective of the snubber cycle test is to (1) display the normal wear and tear for a snubber over an extended period of time, and (2) display the resistance to an abrupt disturbance.

What We Do

We test snubbers at their two modes of operation. We expect snubbers, at high rates of loading, especially impact, to provide very high resistance to movement. At low speeds we expect the snubbers to provide very low resistance to movement.

After Completion

Once the test is completed, the engineers will discuss the data reported and propose alternatives that will aid the value in meeting the drag force’s common criteria of 2% or less than the rated load.

Snubber1
Snubber2
Snubber Cycle Testing for Hydraulic Snubber

For more details view our Recent Snubber Testing Press Release or submit your inquiries via the online inquiry form or contact us at info@pipingtech.com

Helium Testing

The Objective

The objective of the helium test is to locate and calibrate leaks.

What We Do

The unit is filled with pressurized helium and the outside is “sniffed” to detect leaks which are indicated by a mass spectrometer.

After Completion

Once the test is completed, leak areas can be passed rejected or repaired.

Expansion Joint03
Burst Test4
Helium Leak Test for Expansion Joint

For more details view our helium test blog post or submit your inquiries via the online inquiry form or contact us at info@pipingtech.com

Burst Testing

November 14, 2017

The Objective

The objective of the burst test is to determine the ultimate pressure resistance. Primarily conducted on bellows.

What We Do

Normally, hydraulic pressure is slowly increased until failure occurs.

After Completion

Based on the burst test results, a safety factor is applied. This establishes the ultimate pressure rating.

Burst
Proof Burst test for expansion joint
Burst Test2
Leakage area after burst test
For further information, please submit your inquiries via the online inquiry form or contact us at info@pipingtech.com
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