ENGT5257 Design against Failure

Case Study Assignment

Learning outcome 1: Diagnose the type of failure based on the service history, manufacturing processes, fractography and experimental analysis.

Learning outcome 2: Giving feasible suggestions to avoid failures through considering appropriate design approaches, operation services and materials selection.

Scope
Designing machines, vehicles and structures that are safe, reliable and economical requires both efficient usesof materials and assurance that structural failure will not occur. Therefore, this module is appropriate for postgraduate students to study the mechanical behaviour of materials, specifically for topics such as fracture toughness, fatigue, creep and corrosion. Structural Integrity: The design against Failure module covers topics such as types of materials and their properties and types of failure in materials. It also focuses on stress-based fatigue analysis, relatively new methods of fracture mechanics, creep and corrosion resistance.

Part 1: Three Case Studies

For the following three case studies, you are required to:
• Justify the precautions about the failed pieces before starting investigations.
• Discuss the given microstructures and/or fractography of the failed components.
• Diagnose the failure, root causes, and discuss the challenges
• Explore feasible solutions based on theories and research approaches
• Apply or use Failure prediction methods to estimate service life.
• Apply or use Failure prevention methods to act before failure.
• Suggest a feasible Maintenance plan.
• Support your work through images, graphs, charts, references etc.

Case Study One (500 words)
Austenitic stainless-steel plate was used as heat exchanger tubes to produce a steam generator in a water processing plant. The heat exchanger tubes located in the central part were exposed to high heat input during welding of the tubes with the tube wall. The service conditions of the heat exchanger were dry saturated steam (9 bar, 200 oC) for heating softened water, around 36oC, 25 ppm Cl-. After a few months of the operation, numerous cracks on the heat exchanger tubes near welded joints to the tube wall were started.

Case Study Two (500 words)
A martensitic microstructure of low alloy steel, AISI/SAE 4330V, was used as an oil and gas well tubular drilling tool. The tool operated with extreme torque variation, creating multiple cracks at the external diameter, and led to the fracture. The drilling tool was already close to the end of its life.

Case Study Three (500 words)
Case Study Three Part (1)
Two dissimilar metallic alloys, a plate of mild steel with a larger piece of austenitic stainless steel, were lap joint MIG-welded using 308 AISI filler metal, serviced in an oil industry environment for one year.
Case Study Three Part (2)
Extend and improve your selected case study from Coursework (1)

Part (2) Fracture Toughness
Crack length versus cycle data is given in the table below from a test on a centre-cracked plate of 7075-T6aluminium. The specimen dimensions: h = 445, b = 152.4, and t = 2.29 mm. The force was cycled between 10 kN and a maximum value of 48 kN.

o Obtain the da/dN and ?K values.
o Illustrate the Kth and KiC values on a sketched diagram.
o Discuss the methods to increase the life of the component.
Indicate all the graphs, charts and diagrams that will be used to solve this question.

Attachment:- Structural Integrity.rar