Table of Material Properties
Selection
From the above CCR, we see that Brush Wellman Beryllium Copper Alloy and AISI Type S21800 Stainless Steel, Annealed 10% Cold reduction are the top materials. However, because of its cost effectiveness, AISI Type S21800 takes the cake. If we were basing it solely on performance, I would definitely choose titanium or Brush Wellman Beryllium.
Question 5
A fluid cross flow amine heat exchanger is used in a sweetening process and operates at 38 oC and at a pressure of 20 psig. The fluid has some dissolved carbon dioxide and hydrogen sulphide. Select materials for fabrication of the heat exchanger.
Solution:
An Amine Heat Exchanger uses lean and rich amine to exchange heat. This process effectively strips H2S and other corrosive materials from the fluid passing through.
Assumptions:
Constant temperature
Constant pressure
No fluctuations in fluid.
Because the fluid contains CO2 and H2S, we will have to choose metals used for sour application.
From NACE 0176, we know the ideal materials for medium corrosive conditions are steel, stainless steel and brass
Material Data Sheet
Note: many of the costs were unavailable, therefore to find the difference between the different material types (i.e. Naturalized, Annealed, etc.) were found using constant price factors.
The two materials three materials that jumped out at me were AISI 4140 Annealed, AISI 4140 Naturalized, and AISI S20910. When looking at the CCR, we noticed that the best material was AISI S20910. However, we looked closely at the Thermal Conductivity Values (primary condition) of the three metals, we realized that AISI 4140 Annealed and Naturalized had, by far, the highest conductivity. To choose between these two materials, we looked at our other condition, that being the Safety, or ductility. Because AISI 4140 had a higher value ductility factor, therefore we made this our final choice.
Question 6
Some large process refinery piping is to be operated at 650 oC under a pressure of 25 psig. The piping is 24” diameter and carries hot gases that have some oxygen gas along with carbon dioxide and carbon monoxide. Make a selection of materials that can be used for this application.
Solution:
The minimum strength of the material can be calculated using:
Assume thickness is 10 mm
Diameter is 24’’ or 60.96 cm
Pressure is 20 psi or 137 kPa
We calculated the hoop stress to be 4039 kPa.
We also know, that we want to minimize corrosion, and this is directly related to Chromium. Therefore, we would like to maximize chromium.
From the above calculations, we can see that AISI 316 is the best material to choose. It has good chromium content, high ultimate strength, low density, high creep strain, low thermal conductivity and an excellent CCR.
Question 7
A pressure surge tank is to be designed and fabricated for damping out the variable pressure spikes that continually occur in one part of a clean-up plant process. The tank has a rubber bladder secured at the mid point in the interior of the tank. The space above the bladder being charged with nitrogen under pressure. The unit must meet ASME requirements. The unit when completed is to be shipped to the United Arab Emirates. Select the best material for this application.
Solution:
Surge tanks are used as a storage tank for unexpected pressure surges. For example, in the oilfield, many satellites contain surge tanks incase of sudden increases in fluid pressure in separators and other vessels.
The most important thing for this tank is to absorb high pressure surges. The fluids that enter the tank my cause corrosion (especially brine and H2S). Because this is being shipped to the UAE, we must take the density into consideration as well.
Assume:
Cost is an important factor in our material selection.
The temperature is not a high
Safety:
This is very dangerous application and human lives are at stake, therefore it is very critical is safety, and εf > 0.20
It was difficult to find information on surge tanks as there are diverse uses. However, according to ASME requirements, located a few equations which will aid us in our calculations:
σmax = (5/8)*σy
σmax = (1/4)*σu
to find CCR, we used the following formula
CCR = (σy)(σu)(CR)(εf)
(ρ x Cost)
From the above table, we can see that the best choice of material is AISI 304L is the best choice of material. It has high yield strength with decent ultimate strength. Ductility is excellent and the material is cheap to buy. Also, very good corrosion resistance helps its feasibility.
