Piping diagram | Tips for plant beginners to quickly check

piping diagram check
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I will explain points to note when checking the piping diagram of a chemical plant .

A must have for any mechanical engineer.

Even just one plumbing check is full of problems for time and effectiveness.

It would be meaningless if there was nothing to point out even though I spent a lot of time looking at the drawings.

Let’s check it from the viewpoint of reducing construction defects, which is the purpose .

I hope this helps you to maximize your results in the shortest amount of time.

The quality of the piping diagram is directly linked to problems during construction and trial operation. It is one of the checkpoints for mechatronic engineers how to finish the piping diagram accurately. I would like to develop it as a skill to add value.

However, there is a limit to improving the accuracy of piping diagrams. Coordination at the construction stage and command and coordination at the trial run are also skill as an engineer. The labor to check and apply the piping diagram will be distributed while looking at the degree of impact after that. Strategic.

Why is it difficult to check piping diagrams?

It is often said that piping diagram checks in chemical plants are difficult.

There are not many people who talk about this reason, but I think it can be divided into the following three reasons.

3D image is not possible

One of the reasons why piping diagram checks are said to be difficult is that it is not possible to create a 3D image.

It’s certainly difficult if you haven’t trained how to read drawings.

Isometric drawings are effective when trying to have the most important 3D image in a piping diagram.

This isometric drawing gives you a rough idea, but it works to check if the piping layout fits.

However, it is not enough to have an image of on-site work because there is no dimension or layout information.

Therefore, it is necessary to check the isometric drawing and the floor plan.

To see these two drawings, you will have a hard time if you do not know how to read the drawings, especially how to write the third trigonometry.

In the background is the space unit of middle school mathematics.

There are many people who are not good at that.

The weak field is dragged as it is, and it becomes an obstacle when fighting with piping diagrams at the company.

Usually, after graduating from junior high school, the only place where such training is done is high school mathematics.

too many lines

There are quite a few levels of 4km to 5km even at the rationalization level in one construction at a chemical plant.

The number of lines seen on a process basis alone is over 100.

If you look at the piping construction base, you will recognize it as a line volume that is two to three times that.

The pipes are stretched all over the place.

Even if you can have an image of an individual line in isometric, it is quite difficult when it comes to interference with other lines.

Let’s take a look at a few examples.

For example, let’s consider the case where the following single line is arranged in a plan view and an isometric view.

One isometric matching (piping diagram)

If you feel that it will be this easy and have an image of it, you have already passed the test.

Compare these two pictures

  • ○ indicates a flange
  • Flanges are below long pipes
  • That’s why the valve is a pull-out valve

Because I can instantly imagine that.

However, if this becomes two lines, it should be a little confusing.

Two planes (piping diagram)

This alone will make you think.

It’s only natural to wonder what’s going on.

That’s why I match it with the isometric drawing.

For example, this time I was imagining the isometric image below.

Isometric of two lines (piping diagram)

The problem is the handling of the added line valve.

Since there is no information on the height of the valve on the floor plan, it is normal to worry about what kind of configuration it is.

It was an example that if there are nearly 50 such lines on one plane piping diagram, it will take time to check it .

i don’t know what to check

Beginners are always at a loss when checking piping diagrams.

  • There are about 50 sheets
  • About 20 of them have lines stretched around as plane piping diagrams.
  • Check with the remaining 30 isometric images

I wonder how long it will take…

It will horrify you.

Even if you use something like a checklist, it is expected to take a huge amount of time.

And I don’t know what to look at, so I look at it for the time being.

Before I knew it, a week or two had passed.

In the meantime, the construction company’s waiting time is reduced, the estimate assessment time is reduced, and preparations for construction cannot be made .

Many problems arise when mechanical engineers delay checking piping diagrams.

The feature of checking piping diagrams is that it is easy to spend time without having to report and consult with your boss.

Significance of checking the piping diagram

Let’s reconsider the significance of checking the piping diagram.

Piping diagrams form the basis of construction materials for chemical plants.

The piping diagram has the following features in the chemical plant project aspect:

  • large amount
  • Many related industries
  • a lot of trouble

Among chemical plants, it occupies the most space, and the ratio of both cost and construction period is by far the highest.

Furthermore, the degree of freedom in design is extremely high.

If you don’t suppress the degree of freedom here first, the specifications of other facilities and construction will not be solidified.

Piping diagrams are not only for piping work, but also for the purpose of conveying the construction image to surrounding industries.

Piping diagrams have information related to all types of construction work performed in a chemical plant.

As a result, problems are likely to occur on site .

It is very important to check the piping diagram correctly for the purpose of reducing the cost and construction period of the entire project.

Basic stance of piping check

Introducing the basic stance of piping check.

Piping diagram check stance

  • Define the points to be emphasized in the construction
  • Check line by line
  • Try to see the whole with one index
  • Flow the whole in the same way with another index

Points to focus on

Decide which points to focus on in the project.

I divide it into two parts.

  1. Anyway, I just want to be able to drive at least
  2. I want to streamline my work

Mechanical engineers are strongly aware that it is only natural for them to be 100% satisfied with both 1 and 2 in one project.

This is because I see it from a narrow perspective of construction and projects.

It is a plant engineer’s way of thinking that puts the scope on the project .

But from the driver’s point of view, it’s a little different.

In 1, just connect the lines and try driving for the time being → Extract problems while using them → Correctly solve problems in 2.

Drivers have this idea.

Because there is some background…

Thoughts on piping work on the operation side

  • No ability to review piping diagrams.
  • There are too many other things to do besides reviewing, so I don’t have time to review.
  • Opinions of on-site operators differ too much
  • It’s faster to actually use it and find out the problems
  • Can be used as a forum for on-site improvement proposals

Workability is important! The more strongly imprinted engineers are, the more time they spend checking the piping diagram.

It is important to visualize the work on site! After being told that, time passed while looking at the piping diagram while imagining work that I had never done before.

I couldn’t do anything else to check in the meantime.

There are so many examples.

It is true that there are places where workability is important.

Settle in there.

While having the operator review the workability comprehensively, the mechanical engineer also checks only the places where workability is important.

It is important to separate roles.

There are many people who suddenly look at the piping diagram without this definition.

It is exactly the same as reading carefully from the first page in reading.

line check

The basics of checking piping diagrams are the same as line checks.

Basics of line check

  • Is there a flow from A to B?

Simply put, that’s all.

Are the source and destination properly connected?

I am checking this one by one.

It is steady, but there is only this.

After that, it’s a matter of how to allocate the time to hang on each one.

multiple metrics

Even though we check each line, there are a lot of check items.

If you make something like a piping diagram checklist, you’ll know right away.

The checklist should be at least one sheet of A4. Maybe 3 or 4 at most.

Do you do this checklist for each pipe? You should be wondering.

Change your point of view at this time.

I’m going to chase the line anyway with 1 indicators.

for example···

multiple metrics

  1. Are the source and destination connected?
  2. Do you have the correct caliber?
  3. Is the material suitable?
  4. Are accessories such as valves attached properly?
  5. the pipe height is correct or not?
  6. Is there interference between pipes?
  7. work space is secured or not?
  8. Is there any interference with other equipment?

The idea is to divide the loop into multiple times.

If you get used to it, you can check all items at once and end with one loop.

However, if there are many checkpoints, there will always be things that are overlooked, and it is impossible to level the line of sight.

  • The first line is somehow checking only the connection
  • When you look at the second line, remember that pipe height is important.
  • Return to checking the pipe height of the first line.

If you do this, you won’t be able to check all the lines even once, no matter how long it takes.

Let’s just look at the connections in the first loop.

Some sort of division is necessary.

I wrote the general things about checking the piping diagram above, but it is necessary to have some segregation, for example, the connection is the responsibility of the drawing person, and the workability is the responsibility of the operator.

However, if you leave it completely to me, your understanding of piping diagrams will hit a ceiling somewhere.

Let’s be able to think about connection and workability to some extent.

It’s up to each individual to decide when that is.

Matching with P&ID

Here are some representative examples of checkpoints in piping diagrams.

First, check with P&ID.

A piping diagram must match its primary source, the P&ID.

Some of you may be wondering what it takes for granted.

Because of the large amount of piping diagrams, it is an important factor whether each pipe is properly completed.

You may accidentally make a mistake. It looks easy but is actually difficult.

Verification with P&ID requires the following checks.

  • Piping diameter, material, fluid name, heat insulation
  • Merging and branching of piping
  • Flow direction of piping
  • Piping slope, pocket, liquid seal, required dimensions

This information is provided on the P&ID.

It is important to perform a basic check to see if the information is reflected in the piping diagram.

Follow P&ID order

There are several possible patterns for matching a piping diagram with a P&ID.

  1. Follow the piping diagram in the order of the P&ID process
  2. Follow P&ID page by page diagram
  3. Chasing P&IDs in isometric order

Basically, it is method 1.

Operators and process engineers have a single point of view.

Operators may only see isometric drawings.

We will steadily check each page of the P&ID.

Method 2 is also reasonably valid.

Both 1 and 2 start with P&ID, which is the basic material.

Checked records are recorded on the piping diagram side.

The idea is that if you go around the P&ID with this, all lines will be checked on the piping diagram side as well.

On rare occasions, there are people who check the P&ID side, but it is better to quit.

This is because there is no record of how far you have checked out of the huge amount of piping in the piping diagram, so you will not know on the way.

Floor plan as starting point

When checking the line with a piping diagram, first check the plane piping diagram.

The floor plan should include information about the equipment.

Let’s attach the symbol corresponding to the isometric drawing to the flat piping drawing.

piping diagram

If you look at the floor plan and write 1-A, it will be easier to shift your perspective to the isometric drawing based on this symbol.

In addition, I wrote 1 as the page number and A as the serial number.

If the number of isometrics is large and it becomes “22-F”, it will be difficult to have only one serial number.

Check Isometrics

After checking the starting point on the flat piping diagram, let’s check the isometric drawing.

Isometric drawings contain a good deal of plumbing information.

At least, the information related to operation, which is the main part written in the P&ID, is described.

Check the P&ID line changes while looking at the isometric drawing.

Check the pipe material, pipe diameter, valve, reducer, etc.

If there are no problems, check the line with a highlighter or the like.

Oh yeah.

Checking the piping diagram is done on paper.

If you check the floor plan and isometric drawing one by one on the computer, it is very difficult to switch pages.

In terms of searchability and visibility, it can be said that paper is the only advantage over personal computers.

I check with a highlighter pen because it’s easier to draw lines.

Even if you try to draw a line on the line with a ballpoint pen, you will not be able to draw it cleanly.

Sometimes you pull off the line.

With a thin ballpoint pen, etc., when multiple lines are lined up in parallel, it becomes difficult to tell which line was checked.

A highlighter pen is much easier than that.

Any color is fine, but it is better to use one color.

Conversely, if you are checking on your computer, you should suspect that you are not looking at it seriously.

Confirm destination

Finally, confirm your destination.

This is the hardest part of the process.

Too many mechanical engineers give up on this.

After confirming the isometric drawing as a starting point, return to the flat piping drawing and follow the destination.

In a flat piping diagram, piping is laid out like a mesh.

Focus on one of these lines and check if the line is connected to the desired location while coloring the line with a highlighter pen.

If the end point is a facility, also check the isometric drawing around the end point.

Checking the connection is difficult because it covers multiple piping plan views.

However, on-site line checks are done carefully one by one.

Just do this on the drawing.

It’s easier than going back and forth to the site.

It’s only natural for a draftsman to check the connections thoroughly, but don’t leave everything up to you and see it with your own eyes.

Shape of piping

The shape of the piping, which is the essence of the piping diagram, is of course an important checkpoint.


A piping diagram is a document that shows where the shape of piping should be placed in space.

As such, placement information is central.

  • Plant North (North)
  • Equipment layout and position
  • Column arrangement and position
  • Workability (legal, operation, passage, switching)
  • piping route
  • piping header
  • nozzle orientation

You will notice that there are many other things to check besides the plumbing route.

In particular, the viewpoint of workability and traffic is important.

Look at the layout of the equipment and the layout of the piping on the piping plane, and at least check whether it is possible to pass.

If you are desperate to follow the plumbing route, you will be neglected.


Check the accessories on the isometric side.

Accessories are as follows.

  • valve
  • strainer
  • support

This item is easy to check at the same time as destination connection by checking with P&ID .

When creating a piping diagram for valves and strainers, the “face-to-face” distance is not fixed.

After deciding on the piping diagram, the size of the valve changed and could not be attached on site.

Problems like this are popping up like mountains.

It is a delicate line whether the support is included in the accessories or included in others.


The following factors must be considered when designing piping.

It is not essential, but it is important to improve the quality of the plant.

  • Separate hot and hazardous material piping
  • Separate hot and cold pipes
  • Reinforce small diameter nozzles
  • prevent vibration
  • Install earth bonding
  • Proper insulation support

This part is a little more specialized.


It may look fine on the piping diagram, but in fact there are problems.

A typical example is a relationship.

I think more than 50% of on-site construction troubles are caused by misalignment of various connections and changes in routes due to inability to connect pipes.

Communication with equipment

Needless to say, the information is important because the piping is connected to the equipment.

  • checking the equipment drawing
  • Are the device nozzle and the piping diagram consistent?
  • instruments attached to the equipment (liquid level gauge, thermometer) is listed
  • Is the device platform listed?

The connection between pipes and equipment should be checked prior to the connection between pipes.

From a process perspective, the first thing to check is the connection between piping and equipment .

After that, check the plumbing and plumbing information.

Interaction with instrumentation

As with valves, the connection of instrumentation is also important.

Arrangement of instrumentation is not done by piping diagram creators or mechanical designers.

This is generally the responsibility of an instrumentation person.

Missing face-to-face information for instrumentation can be a problem, as is the case with valves.

In addition, space is required for operation and maintenance of instrumentation.

It should be checked on the piping diagram.

In particular, flowmeter headers occupy a large amount of space because they require a straight pipe length.

Since the degree of freedom is narrow, it should be suppressed at the beginning of the piping diagram.

Interaction with civil equipment

Interacting with civil engineering equipment is extremely important.

A plumber who neglects this place will greatly reduce his credibility.

It is fatal if there is a problem that pipes are viewed with beams, foundations, racks, etc.

Modifications to civil equipment cannot be made later.

When this problem occurs, it is necessary to change the route on the piping side.

When a problem occurs, I often worry because the degree of freedom to change is reduced.

You have to create a piping diagram with the enthusiasm that it will never interfere with civil equipment.

Electricity and instrumentation can be anything, and interference with mechanical equipment is checked quite often with piping diagrams, so it is less frequent.

Since civil engineering facilities are difficult to appear in piping diagrams, it is easy to overlook them.


Knowledge of piping design is indispensable for checking piping diagrams.

In addition to the articles on this site, you may also find the following books helpful.

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We have introduced points to note when checking the piping diagram of a chemical plant.

The quality of the piping diagram greatly influences the site construction.

There is a tendency to check excessively from the viewpoint of suppressing rework and reducing additional costs, but let’s carefully verify the check time and its effect.

It is better to check each line like a line check and loop with multiple indicators.

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.