Chemical Engineering In-Plant Training or industrial internship #2

Omkar Mehta
Sep 9, 2018 · 8 min read

Before I start blabbing on what this article is all about, I want to share a few things. The main objective of this series is not to get ready-made answers to all the questions you’ll would have during your internship. This article series shall be a guide-tool to make you more curious and to open your third eye. Generally, third-year students don’t know what to do during industrial internship. This series shall help you in this regard. The efforts to do most of the things I would write here would have to be put up by you.

So, in continuation to the previous article, I intend to cover the functioning of P&ID, what it signifies, and also what you can do in a field visit.

So, in order for me to explain to you the nitty-gritty of P&ID, I am learning to draw P&IDs by watching youtube videos. It is such a pleasing experience to draw P&IDs like shown in the plant. I’ve not yet finished it. But, in coming articles, I’ll cover everything about P&ID. The main objective is not how to draw P&ID, but how to read P&ID. Covering basic points will suffice.

The foremost point in reading P&ID is to knowing symbols.

Let’s start with symbols: Symbols make our lives easier. Trust me, knowing them what they represent is miraculous. Once you are familiar with symbols, things will fall into place quite easily.

P&ID symbols for lines

As I said in my last article that in order to read P&ID, get familiarized with symbols. Draw these symbols, if you want, so as to remember them. On the left image, you can see various lines: Pipe lines(Primary line, Pipe line with steam tracing, Pipe line with steam jacketing), Instrument lines (Electric signal, Pneumatic signal, Software link, Instrument supply line). Among these, the most essential ones to know (this doesn’t mean, others are unimportant. They are, but you’re there for the internship. So, only few would be enough.) are primary line, electrical line, pneumatic signal line, and software link line. If you go to a typical chemical plant, you’ll find that operations people (i.e. us, chemical engineers, process technicians) work in tandem with mechanical, instrumentation and electrical department. Maintaining clear communication among these departments is quintessential for operating the plant successfully. So, ask any operator and an instrumentation guy about the essential lines, and why they are provided.

Symbols for various valves

Among the valves, the noteworthy and attention-grabbing ones (at least for me) are control valve, gate valve, globe valve, needle valve, check valve(non-return valve), ball valve, and butterfly valve. Knowing these valves will provide great insights as to how the valves are arranged in a process line. Why would we, as chemical engineers, arrange valves in a certain way? If you see a control valve in the field, you’ll see that it is followed by a drain valve, an isolation valve; and it follows an isolation valve and a drain valve. Interestingly, a globe valve (perhaps of different size than that of control valve or of same size. Why?) is placed in parallel to it. Why so? Well, ask the operator (or you can always comment here).

Pipe fittings

Among the pipe fittings, the most important ones are the hose, flange connection, blind flange, closed and open blind with flanges. Ask the operator to show these pipe fittings in the field and also ask him why they are provided, and when they would be used.

Instruments

My most favorite symbols in P&ID are the ones under instruments heading. I wish I had studied more about instrumentation during my college days. As you see, DCS (Distributed Control Systems) and PLC (Programmable Logic Controller) are mentioned here again.

Symbol for ‘field discrete instrument’ represents that that instrument is present at a particular location in the field. That instrument is either of the following: transmitter, analyzer, indicator, pressure gauge, temperature gauge.

Symbol for ‘Primary Accessible DCS’ and ‘Primary Accessible PLC’ should be remembered. Why? ‘Primary Accessible DCS’ tag can be seen on DCS screen in control room. This is where panel officer takes action, in order to keep operating values normal.

Primary Accessible PLC’ tag is used in Emergency ShutDown System. In order to shutdown the plant in case of emergency, PLC is used.

As I was saying, in your first week, you read Process description, Process control, Emergency procedures and Trip settings in Operating Manual. Get familiarized with P&ID symbols.

3. In second week, continue reading P&ID diagram and complete it thoroughly.

Since it will take time to read a P&ID diagram, you should dedicate your time into reading it as much as you could. If you get stuck in somewhere, refer Process Flow Diagram (PFD)or DCS, or ask panel officers. (Also, do not disturb them if there is any emergency in the plant. Observe what he/she might be doing. After the emergency is handled, ask them what happened, & how he/she tackled it.)

Making efforts into reading a P&ID book would really make a great difference in life, even if you couldn’t understand it completely.

4. Field visit.

Field visit is must. Spend as much time as you could in the field. Get to know what kind of jobs are done in the field. Interact. Ask questions. Before you go to the field, ask for the permission of the field officer. In order to go to the field, one must have Personal Protective Equipment (PPE) which entails a hard hat, a boiler suit, a pair of shoes with steel cap and an ear plug. (Gloves too, but you’re not going to touch anything in the field. I warn you not to touch anything. This is for your safety.)

Now, go to the field with the perspective of getting as many questions (i.e. be curious) as you could. Ask yourselves, “WHY?” all the time. (When I joined BPCL, I was asked to write down all these questions each week. So far, I have had 400 questions.)

Color coding system.

Let’s say, you want to know what flows in the pipe by just looking at it. By jove, you have color codes. Pipelines will have a specific color, along with circular bands of different colors for different products. Here, cell colour indicates pipe colour in the field, and the colorful stripes indicate what product flows through it as follows.

For Utilities
For Products
For Crude distillation Unit

Websites through which you can learn more about color coding.

Control valves. Red/Green. What’s written on it? Actuator? I/P converter?

You’ll find that the bodies of some control valves are painted red and some green. Ask operator why this is so. (Hint: Do you know anything about air-to-open and air-to-close valves? If not, google and read about it. This has everything to do with shutdown process of any plant.)

Please know how a control valve works from this link. When you go out in the field, try to discern the parts of the control valve (like, actuator type, I/P converter, air pressure gauges, etc.)

On the body of control valve, numbers and some letters are scribbled. Ask operator what it signifies. Or find this online.

Isolation valve/ Drain valve/ Block valve/ Non-return valve(Check valve)

All valves are either gate valve, globe valve, butterfly valve, ball valve etc. But depending upon its application in operation of the plant, these valves are classified into: isolation valve, drain valve, block valve, non-return valve. The field officer would tell you more about this.

(Also, as a funny assignment, try to know what valves are used in plumbing system in bathroom)

Can you identify which is a Globe valve and which is a Gate valve?

This field visit shall be an excellent exercise for you all to find which valve is a gate/globe valve. There are few distinct points by which you can do so.

Gate valve
Globe valve

Pumps: Suction pressure, discharge pressure, Power rating in KW, Over Amp, coupler.

Note down the suction pressure, discharge pressure and power rating of all the pumps. This shall help in knowing which pump of what power to be used in your final project.

There will be ampere reading in the field. Ask your operator what an overamp value is and what is its significance.

Where is ‘coupler’ used in pump? Coupler connects motor to pump. When motor doesn’t work well (Operator finds this either by vibrations or high temperature of it/OverAmps), electrical department does No-Load test of motor after decoupling coupler.

Sample points for gas, liquid.

Ask operator to show you how a gas is collected for sample to be used for testing in lab. (Similarly, for liquids.)

Chemical dosing (if any)

Few chemicals are used to maintain pH, hardness, dissolve oxygen level. Dosing pumps are used. How frequently do they use it?

Terminologies

Backpressure: Pressure generated on upstream pipelines due to closing of valve in downstream.

Passing: A valve is passing when it leaks even if valve is shut completely.


“ Any fool can know. The point is to understand. -Albert Einstein.”

Omkar Mehta

Written by

B. Chemical Engineer from ICT (UDCT, Mumbai), Operations Officer @BPCL, Mumbai Refinery. Aspiring Data Scientist.

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade