1. Fabrication Selection
Materials
and
Fabrication Selection

2. Chapter outline: Classes of materials (categories of materials)
Materials selection criteria
Material properties
Commonly used materials of construction
Materials fabrication steps
Economic selection of materials
Analysis of failure for metals (types of failure, finding primary cause of failure and initiate corrective action to prevent repetition).

3. Classes of materials

4. Materials selection criteria
The most important characteristics (criteria) to be considered when selecting a material of construction are:
Mechanical and physical properties
Corrosion resistance
Ease of fabrication—forming, welding, casting
Availability in standard sizes
Cost

5. Mechanical and physical properties
a. Strength–tensile strength;
b. Stiffness:
c. Toughness–fracture resistance;
d. Hardness–wear resistance;
e. Fatigue resistance;
f. Creep resistance.

6. Tensile Strength (UTS)
is a measure of the basic strength of a material. It is the maximum stress that the material will withstand, measured by a standard tensile test.
Stiffness
the ability to resist bending and buckling. It is a function of the elastic modulus of the material and the shape of the cross-section of the member.
Toughness
The ability to absorb impact energy.
It is a measure of the materials resistance to crack propagation or measure of ductility.

7. Hardness Fatigue Creep
is an indication of a materials ability to resist wear or scratching. This will be an important property if the equipment is being designed to handle abrasive solids, or liquids containing suspended solids which are likely to cause erosion.
Failure which is likely to occur in equipment subject to cyclic loading; for example, rotating equipment, such as pumps and compressors, and equipment subjected to temperature or pressure cycling.
Fatigue
Creep
Creep is the gradual extension of a material under a steady tensile stress, over a prolonged period of time. It is usually important only at high temperatures.

8. 2. Corrosion resistance
The conditions that cause corrosion can arise in a variety of ways.
It is convenient to classify corrosion into the following categories:
1. Uniform corrosion;
2. Galvanic corrosion–dissimilar metals in contact;
3. Pitting–localized attack;
4. Intergranular corrosion;
5. Stress corrosion;
6. Erosion–corrosion;
7. Corrosion fatigue;
8. High-temperature oxidation and sulfidation;
9. Hydrogen embrittlement.

9. Intergranular corrosion

10. Stress corrosion

11. Erosion–corrosion
Increase in the rate of deterioration or corrosion because of relative movement between a corrosive fluid and the metal surface.
Factors affecting rate of corrosion:
Nature of metal.
Surface film.
Velocity.

12. Erosion–corrosion

13. Hydrogen embrittlement
loss of ductility caused by the absorption (and reaction) of hydrogen in a metal
Ex: Hydrogen reforming plants
H2 embrittlement severity depends on:
Partial pressure of hydrogen
Temperature

14. SELECTION FOR CORROSION RESISTANCE
In order to select the correct material of construction, the process environment to which the material will be exposed must be clearly defined. In addition to the main corrosive chemicals present, the following factors must be considered:
1. Temperature—affects corrosion rate and mechanical properties;
2. Pressure;
3. pH;
4. Presence of trace impurities
5. The amount of aeration—differential oxidation cells;
6. Stream velocity and agitation—erosion-corrosion;

15. Acceptable Corrosion Rates
ipy = inch per year
mpy = mills per year ( 1 mill = 10-3 inch)

16. Commonly used material of construction
Iron and steel
Alloy steel
Nickel and its alloys
Copper and its alloys
Lead
Aluminum

19. II- NONMETALS Plastic materials Ceramic materials
PLASTICS AS MATERIALS OF CONSTRUCTION FOR CHEMICAL PLANTS
They can be divided into two broad classes:
1. Thermoplastic materials, which soften with increasing temperature; for
example, polyvinyl chloride (PVC) and polyethylene.
2. Thermosetting materials, which have a rigid, cross-linked structure; for
example, the polyester and epoxy resins.
II- NONMETALS
Plastic materials
Ceramic materials

20. FAILURE-MODE EFFECT ANALYSIS [FMEA]
Reasons for failure
Design deficiency
Materials problem
Overload (abuse)

21. Failure analysis steps