Hi there, and welcome to this lecture on process flow diagram equipment summary tables. My
name is Marina Miletic. Once you've selected the type and drive of compressor, turbine
or pump, you should next specify the materials of construction for that piece of equipment.
Materials of construction is often abbreviated MOC, and is the specific metal or material
which the piece of equipment is made of. Selecting the right materials of construction is important,
because the process fluid will be in contact with this surface, so it must be able to withstand
the temperatures and the chemical exposure to the stream. Just as with type or drive,
CHEMCAD or Aspen will not select the appropriate material for your piece of equipment. You
must select this by weighing two important factors: the cost of the material versus the
durability required to withstand the temperatures and chemical components. We know why cost
is important, but let's take a minute to talk about what durability really means. The durability
of process equipment is usually determined by how resistant the material is to high temperature,
reactivity, and corrosion. You'll notice that pressure is usually not as important in selecting
materials of construction, because most materials can be manufactured with the appropriate wall
thickness to withstand most pressure requirements. It's very high and very low temperatures that
pose more of a challenge to materials, not only because they can compromise the integrity
of the material, but also because high temperatures almost always increase the rate of reaction
between components in the process stream. Additionally, high temperature also increases
the likelihood of a reaction between the process stream and the surface material. If the process
stream is already potentially reactive, corrosive, oxidative, strongly acidic or basic, this
makes choosing a more durable material all that more important. As you might expect,
if you need a material which can withstand high temperatures and reactive chemicals,
it will most likely cost more. As we briefly discuss some of the most common choices for
materials for large chemical processes, you'll notice this trend. There are about seven different
materials commonly used for process units. It's important to note that all of these materials
are classifications, and their compositions can vary based on the specific variety that's
chosen. Of all groups of materials used in chemical process units, the most ubiquitous
is carbon steel, abbreviated CS. Carbon steel, like all steels, is mostly iron, and it features
up to 2.1% carbon, which is added for hardness. Carbon steel is probably the most widely used
material in chemical processes because it's cheap and it can withstand fairly high and
low temperatures, so long as the process fluid is not corrosive or reactive. Low alloy steels
are a little stronger than carbon steel because they usually incorporate chromium, molybdenum,
and nickel, among other metals and nonmetals, at levels of less than 5%, which means these
materials can be exposed to mildly acidic and mildly oxidizing chemicals. Stainless
steel, abbreviated SS, is a very common material used for process equipment, especially when
minimizing contamination is a necessity. Stainless steel is mostly iron, with fairly high levels
of chromium and nickel, along with manganese, molybdenum, and other metals and nonmetals.
The two most common types of stainless steel used in process equipment area 304, which
is also called 18-8 stainless, and 316 stainless, both of which feature around 20% chromium
and 10% nickel. These materials are used widely because they resist corrosion and reactivity
with many acids and bases, so long as the concentration is not very high. Stainless
steel is also used for very low and high temperature applications, up to around 1100 degrees Centigrade.
Aluminum, abbreviated Al and aluminum alloys are mostly made of aluminum, and are great
choices when a light, corrosive-resistant material is required. Aluminum is one of the
best choices for a material when very cold refrigerants are being used. Copper, abbreviated
Cu and its alloys which include brass and bronze, are mostly made of copper. Brass is
an alloy of copper and zinc, while bronze is copper and usually tin, though other metals
and nonmetals can also be used. Copper alloys are a good material to use for heat transfer,
and for most chemicals, except oxidizing acids like sulfuric or nitric acid. Nickel, abbreviated
Ni, and its alloys including Monel, Inconel, Incoloy, and Hastelloy, are the best class
of metals to use for high temperature applications and very reactive chemicals. The ally Monel
is mostly nickel with up to 34% copper, and a small amount of iron along with other elements.
Monel resists salt water, sulfuric and hydrochloric acid, and caustics such as sodium hydroxide.
Inconel and Incoloy are mostly nickel with up to 30% chromium, as much as 40% iron, and
up to 10% molybdenum, among other metals and nonmetals. The difference between Inconel
and Incoloy is that Inconel is up to 72% nickel, up to 25% chromium, and up to around 20% iron.
Incoloy has less nickel but more iron. Inconel and Incoloy are good to use at high temperatures
and with chloride-containing chemicals. Hastelloy is mostly nickel with up to 30% chromium and
up to 29% molybdenum, along with tungsten, iron, cobalt, and other elements. Hastelloy
is good to use with high concentration oxidizing chemicals, such as peroxides, nitric acid,
and sulfuric acid. Lastly, one of the most expensive materials you can select is titanium,
abbreviated Ti. Its alloys are lightweight and safe to use for almost all organics, acids
and bases, except chemicals such as hydrofluoric acid or concentrated sulfuric acid. Next,
we'll discuss how you should incorporate all this information to make an appropriate selection
for the type of material for each piece of equipment. When selecting a material, look
at the inlet and outlet temperatures and concentration breakdown of all the components in the stream
or streams going through the equipment. When you look at the temperature of the stream
moving through the piece of equipment, check to see if it's below -45 or above 480 degrees
Centigrade. If so, you should probably not use carbon steel, and you'll need to consider
stainless, nickel alloys, or other options. Next, look for oxidizers, chlorides, acids
or bases in the stream going through the piece of equipment. If you see these or any other
potentially corrosive or reactive chemicals at significant concentration levels, look
in a design book or on a materials safety data sheet to see which materials are recommended
for those chemicals. Peters, Timmerhaus and West, and other design books, have chemical
and material compatibility charts for many common chemicals. If you cannot find an exact
chemical listed in a compatibility table, look for a chemical that's similar to it.
For example, if you have palmitic acid as a component in your stream and you can't find
palmitic acid listed in the compatibility chart, find an analogous chemical such as
stearic acid. Using this information, you can now make a list of potentially safe and
compatible materials, considering the components in the stream, and then calculate or estimate
the cost of that piece of equipment made with those materials to narrow it down to a final
selection. Most design textbooks provide tables or software to help you calculate the cost
of units with different materials of construction. If you're not sure if it's necessary to use
a more expensive material because it seems to be on the borderline of being reactive
or damaging to the material, consider using cladded materials. Cladding is when one material
is on top of another as a protective layer. Some common cladded materials used in the
chemical process industry are stainless-clad carbon steel, which is carbon steel with a
layer of stainless, or nickel-clad stainless steel, which means a layer of nickel over
stainless steel. Notice that the less expensive material is always cladded with a more expensive
layer. Choosing a cladded material is a good idea when you're not sure if your stream falls
in a safe compatibility range using a cheaper material. Using cladded materials can also
save a lot of money on initial costs compared to using a non-cladded, more expensive unit.
Although not all pieces of equipment can be made with clad material, it's a good option
to keep in mind for reactors, shell-side heat exchangers, towers, and vessels. For our ethylene
oxide process, oxygen is a common oxidizer, so I chose 316 stainless steel for this compressor,
but I felt that carbon steel was more appropriate for the ethylene stream going through C-102,
since it's not as reactive with metals. I chose carbon steel for this turbine, which
has CO2 and oxygen flowing through it, since this stream is fairly inert, and shouldn't
cause significant oxidation, and I chose 316 stainless steel for this pump, since it has
a very high concentration of ethylene oxide going through it. However, as a mild oxide,
it's not as damaging or reacting as a strong acid or base, so I don't feel that using a
nickel alloy would be necessary. Notice that I chose these materials only after doing quite
a bit of research on the chemical properties and reactivity of these chemicals. It's a
good idea to look up material safety data sheets and chemical property data for each
chemical in your process, not only to help you select the best material for each piece
of equipment, but also because it's important to be cognizant of any potential safety hazards.
I strongly suggest you look in Peters, Timmerhaus and West, or in Turton, Bailie, Whiting and
Shaeiwitz's design books, because both have pages of chemical compatibility charts. These
charts give you materials of construction recommendations based on the chemicals in
your process. Be sure to look in the material and fabrication selection chapter of Peters,
Timmerhaus and West, or the estimation of capital cost chapter in the Turton, Bailie,
Whiting and Shaeiwitz book to find these charts. This is one of the best and easiest ways of
narrowing down and supporting your materials of construction choice. In the next lecture,
we'll look at the rest of the information that should be provided in the equipment summary
table for compressors, turbines, and pumps.