Autoclave Upgrade for Corrosion Fatigue Testing

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Sponsors
Team Name Autoclave Experts
Duration Summer 2018 - Fall 2018
Faculty Adviser
  • Dr. Steven Beyerlein
Mentor
  • Nicholas Schaber
Client
  • Dr. Robert Stephens
Team Members
  • Bahram Sobbi
  • Titus Hansen
  • Kevin Brewer
  • Larry Schwab
  • Tyler Jones

Expand the University of Idaho’s current fatigue testing capabilities to include an autoclave load frame that supports testing of metals as well as operating conditions experienced in nuclear power plants.






Problem Definition[edit]

Background[edit]

Cortest autoclave at U of I with no load frame functionality
Similar load frame/autoclave combination system from Cortest
Image courtesy of cortest.com

The objective of this project is to expand the University of Idaho’s current fatigue testing capabilities to include an autoclave load frame for use in fatigue testing of materials with a focus in metals to be used in nuclear power plants. Currently, no system is on hand to accomplish the fatigue testing environment desired by Dr. Stephens. Currently, there are two load frames with furnaces capable of reaching temperatures up to 700°F, but neither of them have an airtight seal installed. The proposed new system will be able to tolerate temperatures of up to 750°F and 3000 psi while delivering 10,000 lbs of force.

Currently, the lab’s load frames can do fatigue creep testing in an air environment. Fatigue tests slowly apply a tensile load which tears apart a specifically shaped sample over an extended period. The growth rate of the crack is of interest because it is used to predict the lifespan of the material in other applications. The proposed system will perform the same style of tests but will be capable of testing the response of the material to corrosive and pressurized environments.


Deliverables[edit]

The scope of this project includes designing/purchasing all of the components for the fatigue testing apparatus, assembling it, and testing it for proper usability as defined in the following deliverables.

Initial Client Meeting & Expectations
The initial client meeting was conducted on June 14th, 2018. Dr. Stephens and Nicholas Schaber prepared the following list of Primary Objectives for the project.

  • Load Frame Upgrades
    • Loading system (motor/drive/gearbox, rated to ≈10 kips)
    • Load cell (coinciding with applied loads)
    • Load cell calibrated in line with seal
    • Load train displacement measurement (LVDT)
    • Extension rates up to 0.05 mm/s
    • Lid lifting/holding device
  • Load Control and Measurement
    • Feedback control loop (load controlled)
    • User interface for load frame
    • Programmable loading waveforms including:
      • Variable strain rate
      • Fatigue (cyclic loading, variable frequencies)
      • Creep-fatigue (variable hold time and set loading)
      • Constant load
    • Crack measurement/monitoring (DCPD)
    • User interface over/under warnings (temp, pressure, load)
  • Autoclave Upgrades
    • High temperature/pressure dynamic seal
    • Lid modifications
    • Loading rod
    • Internal load support
    • Isolated through-lid fittings for DCPD wires
    • Operating temperature of 400°C (≈750°F)
    • Operating pressure of 20MPa (≈3000psi)

Specifications
Utilizing the above list of deliverables from the client, a refined list of specifications has been produced. The full document is available in the "Additional Documentation" section.

The following is a shortened list of our most important specifications and deliverables.

  • Functionality
    • UI should emulate that of other load frame currently in use by U of I
    • Emergency stop function digitally via LabView UI and mechanically via physical “button”
    • Extension rates up to 0.05mm/s during testing
    • The loading system (motor/drive/gearbox) design shall be able to deliver a maximum load of at least 10,000 pounds.
    • Design shall be able to accommodate standard sized test specimens
    • All components shall have 99% reliability. A DFMEA will take this into account
    • Programmable loading waveforms including:
      • Variable strain rate
      • Fatigue (cyclic loading, variable frequencies)
      • Creep fatigue (variable hold time and set loading)
      • Constant load
    • Crack measurement/monitoring via DCPD
  • Evironmental Requirements
    • All internal autoclave components shall be designed to withstand temperatures of at least 400° C
    • All internal autoclave components and seals shall be designed to withstand pressures of at least 3000 psi
    • All internal autoclave components and seals shall be designed to withstand the same corrosives as the 316H stainless steel that the autoclave is made of

Acronyms used in this text

  • UI: User Interface
  • LVDT: Linear Variable Differential Transformer
  • DCPD: Direct Current Potential Drop

Design Considerations[edit]

Figure 1 - Block diagram of initial design concept

Project Learning[edit]

The autoclave load frame system being developed has many components, but the two requiring the most research and consideration are the Dynamic Seal and the Actuation System.

Dynamic Seal[edit]

With the design shown in Figure 1, a rod is moved linearly through the top of the autoclave pressure chamber. This requires a strong, Dynamic Seal to handle the movement of the rod while containing the required maximum temperature, pressure, and corrosive environment.

One of the seals considered is a Stuffing Box. According to Wikipedia, a stuffing box is an assembly which is used to house a gland seal. It is used to prevent leakage of fluid, such as water or steam, between sliding or turning parts of machine elements.

  • Advantages
    • Inexpensive
    • Easy Maintenance
    • Simple Design
  • Disadvantages
    • Short lifespan of packing material (frequent maintenance required)
    • High friction on load arm
  • Potential Source and Cost
    • MSC (Manhatten Supply Company) sells the packing material at $10/ft.
Spring Seal
The original uploader was Jean-Jacques MILAN at French Wikipedia. https://commons.wikimedia.org/w/index.php?curid=4860492

Another option considered is a spring seal, which is a shaft seal with a Garter Spring contained within the seal to provide compression around the shaft and prevent leakage.

  • Advantages
    • Quickly responds to changes in pressure or temperature
    • Proven system for this application
  • Disadvantages
    • Requires external cooling
    • Easy to damage
  • Potential Source and Cost
    • We sourced this from Cortest at $75.
Metal Bellows
By Корниенко Виктор - Self-photographed, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8058215

The next seal considered is a Metal Bellows. Wikipedia defines metal bellows as elastic vessels that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape (provided the material has not been stressed past its yield strength).

  • Advantages
    • Handles conditions without modification
    • Ease of integration with current system
  • Disadvantages
    • Requires additional safeguards in case of failure
    • Limited range of motion
  • Potential Source and Cost

Actuation System[edit]

Referring again to Figure 1, an Actuator System is needed to raise and lower the gripper arm attached to the test specimen. This system needs to be robust enough to provide the test loads required for fatigue testing of the specimen.

Hydraulic[edit]

  • Advantages
    • Capable of delivering faster load frequencies (15-60 Hz)
    • Higher max speed ramp up rate and turnaround rate
    • Significantly less expensive
    • More commonly available components
  • Disadvantages
    • Requires an external pump and cooling
    • Larger amount of individual components
  • Potential Source and Cost

Electric[edit]

  • Advantages
    • Simpler system (less individual components)
    • Smaller footprint in lab
  • Disadvantages
    • More expensive overall
    • Slower load frequency capabilities (~1 Hz)
    • Lower Lifetime
  • Potential Source and Cost

Final Design[edit]

Validation[edit]

Team Members[edit]

2018 AutoclaveExperts TylerJones.jpg
Tyler Jones

Major: Mechanical Engineering
Hometown: Twin Falls, Idaho
Graduation Date: Fall 2018
Future Goals: Nuclear Propulsion Engineering with the U.S. Navy
Email: jone9289@vandals.uidaho.edu


2018 AutoclaveExperts TitusHansen.jpg
Titus Hansen

Major: Mechanical Engineering
Hometown: Lewiston, Idaho
Graduation Date: Fall 2018
Future Goals: Make the greatest pooper-scooper of all time
Email: hans2993@vandals.uidaho.edu


2018 AutoclaveExperts BahramSobbi.PNG
Bahram Sobbi

Major: Mechanical Engineering
Hometown: Twin Falls, Idaho
Graduation Date: Fall 2018
Future Goals: Make an impact in assistive robotics for stroke victims
Email: eila8850@vandals.uidaho.edu


2018 AutoclaveExperts LarrySchwab.jpg
Larry Schwab

Major: Mechanical Engineering
Hometown: Lewiston, Idaho
Graduation Date: Fall 2018
Future Goals: Improve manufacturing procedures for family owned companies
Email: schw6218@vandals.uidaho.edu


2018 AutoclaveExperts KevinBrewer.jpg
Kevin Brewer

Major: Mechanical Engineering
Hometown: Lynnwood, Washington
Graduation Date: Fall 2018
Future Goals: Advance manufacturing processes through improved industrial automation
Email: brew2002@vandals.uidaho.edu


Additional Documentation[edit]

Project Schedule

2018 AutoclaveExperts GanttChart.jpeg


Meeting Minutes

File:2018 AutoclaveExperts MeetingMinutes.pdf


Product Requirements

File:2018_AutoclaveExperts_ProductRequirementsR2.1.pdf


Client Interview

File:2018_AutoclaveExperts_QuestionsForClient.pdf


Team Contract

File:2018_AutoclaveExperts_TeamContract.pdf