I will explain pipe trace and pipe jacket as temperature control methods for piping in chemical plants.
Keeping pipes at a constant temperature is essential for stable process operation.
Although heat retention performance is required, it tends to be neglected in terms of design because it has a strong tendency to be installed on site.
Some people even give up thinking that it is the same as the conventional method.
If you aim to be an engineer one step higher, you should understand even the characteristics alone.
There are many traces for heat insulation of piping
Chemical plants handle processes with a wide range of temperature conditions.
Some say , “I want to keep this condition as much as possible.”
- I want to heat the process … When it cools down, it solidifies or crystals appear.
- I want to cool the process … the crystals melt when heated
At the reactor level, it can be handled by making it with a jacket.
If it’s just the reactor, it’s fine, but there are times when you want to thoroughly keep the temperature of the piping that connects the reactors.
Plumbing traces come into play here.
There are cases where the plumbing confidence is jacketed, but it is expensive.
In order to quickly adjust the temperature, it is still a piping trace.
However, this plumbing trace also has several patterns.
There are probably many engineers who are troubled without knowing the pattern.
This time, I will explain how to trace the piping.
A simple or bare pipe is shown below before the traced pipe.
It’s just a rectangle, but please think of it as a pipe.
Wrapping trace pipe
When constructing trace piping, you will usually have the following image.
A small-diameter pipe is wrapped around the outer circumference of the pipe, and heat insulation is applied to the outer circumference.
Also called spiral winding.
It is a method for heating and cooling all directions of piping somehow evenly.
However, with this method, the liquid will definitely accumulate in the trace piping.
After a certain number of years, it becomes clogged and unusable.
Hot water pipes are a typical example.
Hot water that is highly corrosive and a hotbed for sludge and slime.
There is a high possibility that the liquid will not flow because it will accumulate and harden in the piping.
Basic form
Start with the basics.
Place one trace along the bare pipe.
Just gently add the trace
Basics are important.
The trace is usually attached to the bottom of the pipe.
This is because the heated liquid becomes lighter in specific gravity and moves upwards, which acts in the direction of equalizing the temperature inside the pipe.
If it is attached to the top, the liquid at the top of the pipe will be heated locally, which is dangerous.
There are very few cases where it is taken seriously.
If you care about it, use jacketed piping.
The place where this pipe can be used as much as possible is the place where spiral winding and jacketing cannot be done.
Specifically, around pumps with glass lining or fluorine resin lining piping.
For glass lining and fluororesin lining piping, connect special pieces together.
In addition to straight pipes, individual pieces such as elbows and cheese can be joined together.
A pump header connects several of these pieces together.
Then, the piping flange will be like a mountain.
Spiral winding is not possible here.
Jacketed piping with glass lining or fluororesin lining is not normally used.
It is far better to jacket Hastelloy-based highly corrosion-resistant metal piping.
But even that is expensive.
That’s why I build traces.
Then we come to the conclusion that we have no choice but to gently add the traces.
Two
If one is not enough, then two is fine.
This is also an easy method.
If two is not enough, then three.
This area is determined by the pipe diameter and the temperature inside the pipe.
Most places where batch chemical plant tracing is required can be completed with just one.
This is because we rarely handle process liquids that exceed 80°C.
Spiral
I want to maximize the effect with a single trace.
If you think so, you can think of spiral winding.
Also called spiral winding.
It is a method for heating and cooling all directions of piping somehow evenly.
Be careful with spiral winding.
This is because the liquid in the trace has a structure that absolutely does not come out.
a typical example; hot water piping is.
Hot water that is highly corrosive and a hotbed for sludge and slime.
It will clog up soon.
You have to use it on the assumption that it will be replaced when it gets clogged.
This is a direction that does not match the needs of the factory, which requires operation management and wants to reduce the number of operators.
Not recommended.
double trace
It’s a pretty rare case, but there are examples like this.
Hot water tracing on the inside, steam tracing on the outside.
pretty crazy.
This is the case when the thermal stability in the pipe is critical.
Steam tracing over 100°C will warm the contents too much.
Hot water trace on the inside to dislike this.
However, when it’s cold, such as in winter, the temperature of the hot water drops too much and I don’t like it.
So wrap the steam trace around the outer surface.
This is the idea.
It’s a world where there are only a few in one plant.
Material
Materials are always a hot topic in trace piping.
Is it a copper pipe or a steel pipe ?
Easy to use is whether it is easy to wind
Copper pipe is much easier to wind.
Copper pipes have a smaller diameter and are more prone to clogging.
Ease of construction, which is not possible with steel pipes, is an advantage.
Usually copper pipe.
This understanding is enough.
Occasionally, copper will not work.
This is determined by the process.
It is famous in this world that the triple bond acetylene and copper form copper acetylide.
caliber
There are also several types of trace diameters.
- Copper tube Φ10 or Φ12
- Steel pipe 15A
If it’s a copper tube , Φ10 is naturally easier to wind, but it’s also easier to clog.
If possible, it would be better to unify to Φ12.
Since the existing facility is Φ10, it remains Φ10.
Steel pipe can be wound at SGP’s 15A, but it costs money to bend it.
The use of steel pipes should be limited to cases where copper pipes are dangerous.
Precautions for trace piping design
Here are some points to keep in mind when designing trace piping.
long distance piping
Let’s start with the basic long-distance piping.
For long-distance piping, traces are taken again at regular intervals.
image as shown below.
Take trace pipes at 50-100m intervals.
In cold climates, it may be 50m.
This depends on the amount of drain that occurs in the trace.
Even on the TLV site, it says that it will be decided “experimentally and empirically”.
Please tell me the proper length of trace pipe for steam tracing.
Heating pipes with traces is not really practical.
If anything, the aim is to ” not cool the piping”.
Pipes with traces do not cool down, and the heat of the traces flows through the heat insulation to the outside air.
If no trace is attached, the heat inside the pipe will gradually escape to the outside through the insulation.
Using heat insulation only slows down the heat transfer rate.
New liquid (new heat) is constantly supplied to the inside of the piping by a pump or the like, but some of that heat continues to escape to the outside.
It is easier to understand if you think that traces are attached to prevent this amount of heat.
Strictly speaking, there is also heat transmitted from the trace to the piping,
The conditions are complicated to calculate and obtain at the field level, and the results commensurate with the effort cannot be obtained.
Be careful to overlap the parts where the traces are cut off.
If you do not overlap, you will have areas where the heat of the trace is not transferred.
It’s a small detail, but be careful.
Pay attention to pressure loss
Now, let’s look at retaking traces at regular intervals from a chemical engineering point of view.
- Pressure loss occurs and steam flow rate decreases
- A pressure loss occurs, and the driving force for drain discharge decreases.
- Pressure loss occurs and steam temperature drops
The key word is ” pressure loss“.
It looks like the image below.
The trace pipe actually branches off the steam main.
Since the steam main pipe has a large diameter, there is almost no pressure loss at a distance of 50 to 100m.
On the other hand, trace piping has a small diameter, so a small amount of pressure loss occurs.
As a result of transmitting the heat of the trace to the piping, the steam condenses in the drain and the volume decreases, resulting in less pressure loss.
When the inside of the trace tube is completely drained, the function of transferring heat is almost lost, and it must be discharged.
Steam pressure in the trace tube acts as a driving force to expel the condensate.
If the pressure loss is too large, the driving force will be lost.
Of course, there is also the disadvantage that the steam temperature drops as the pressure loss occurs and the steam pressure drops.
Naturally, let’s properly discharge the drain with a steam trap.
Bypass piping
Bypass piping is a classic example that requires attention.
See the diagram below.
The left side is ideal trace piping, and the right side is an example of a common failure.
In the example on the left, steam flows in one pass through the trace pipe.
If it is on the right side, the trace piping will be branched.
The pressure drop is higher on the bypass side where the trace pipe length is longer, so the flow rate is lower.
If there is equipment (such as a flow meter) that needs to be kept warm on the trace piping side, it’s putting the cart before the horse.
In the case of the example on the right, there are cases where the piping diagram is drawn without even being aware of the branching of the trace piping in the first place.
“I just put a dotted trace line next to the practice that is the main one.”
Thank you.
If you submit such a piping diagram, the construction company will be troubled.
If you have a consultation, we can respond, but it is troublesome if it is constructed on your own.
This is because trace may be omitted on either the bypass side or the main side . The main side is often omitted.
header piping
Finally, there is the header piping.
See the diagram below.
The example on the left is the correct answer. An example of failure is shown in the middle. The right is the middle follow example.
It is preferable to place the traced piping at the end of the header to allow the trace to wrap around the entire header.
Of course, there are many things that cannot be done according to the philosophy of the plant.
The end of the header is often soaked with cleaning fluid.
If you install traced tubing somewhere other than at the end, the dead end of the header may not have trace wrapped around it.
Let’s divert the trace all the way to the end of the header to follow along.
It is a point to check not only the piping diagram but also the construction at the site.
Characteristics of jacket piping
In addition to trace piping, there is a method called jacketing.
The jacket has a high heat exchange efficiency, but there is a problem that it is difficult to install.
The elbow is not too bad, but the cheese part is very difficult.
There is no point in choosing jackets for areas with complicated piping shapes, such as around headers.
If the jacket leaks, it will be difficult to repair, and you will have to replace the entire piping.
In that case, the trace is less damaged.
half jacket
A half jacket is one in which the area around the end flange is not jacketed.
A half jacket is the basis of the jacket method.
This is because it is easy to make.
A nozzle is attached to the end of the half jacket, but since the liquid continues to accumulate at the true end, it is difficult to contribute to heat exchange.
Since a flange cover is attached to the area around the flange anyway, there are many cases where you don’t need a full jacket or even if the jacket fluid accumulates, you don’t have to worry about it.
The jacket method is also in the lineup for glass lined piping, but the half jacket is the basic.
full jacket
A full jacket is the opposite of a half jacket.
A jacket is attached to the end of the pipe, isn’t it?
It may be used when you want to avoid heat loss even a little.
Note that the inner pipe flange diameter is increased by several sizes .
This is because the diameter of the full jacket flange is determined by the diameter of the outer pipe.
Even with a full jacket, the position of the jacket inlet and outlet nozzles cannot be shortened much, and there is only a dead part, so it is not very good.
Dare I say it, I feel that there are a little more cases where it is used for leak detection purposes than for piping heating purposes.
Dare I say it, I feel that there are a little more cases where it is used for leak detection purposes than for piping heating purposes.
reference
Tracing and jacketing are also special methods in plumbing.
Although it is important for practical work, it is better to acquire general knowledge about plumbing first.
Related information
Related information
lastly
I explained traces and jackets used for temperature control of piping in chemical plants.
Single construction, double construction, spiral winding, diameter, material
It is necessary to design with some awareness of pressure loss, such as between traces and around headers.
If tracing is absolutely useless, use jacket piping.
Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (The comment section is at the bottom of this article.)
*I will read all the comments and answer them seriously.