What is PSI?

What is the PSI definition? Very concise and can be understood by anyone!

If you are a person who often buys iron and steel, or works in the field of pipeline construction.
Surely you will notice that in most specification sheets, manufacturers’ catalogs have the presence of a quantity that is test pressure (in units of psi or in some other brands it is psi). kPa).
So you wonder what PSI is? And why does the manufacturer take it to represent the bearing capacity of its product?
>>> Don’t confuse PSY with Oppa Gangnam Style lyrics!

giphy-gangnam-style
In the process I researched the topic “What is Psi?”, I encountered many, many difficulties.
Because of the documents and articles I read online, the information is very mixed.
Each had their own ideas, and others had a sketchy explanation, insufficient information, and evidence to prove it. People are too specialized, maybe only a few masters and doctors can understand.
Most typical, perhaps the origin of this unit.

At that time, I was very uncomfortable. Because I have to spend too much time on something that has no real value to me. If I don’t want to say that to me, it’s spam.
what-the-hell
And I am sure of one thing, there are many people out there in the same situation as me.
So I decided to do this post.
After many days of tinkering in the sea of information, this is what I have learned.

What is PSI?

Summary: “PSI stands for Pounds Per Square Inch, and Psi is one of the units that represent Pressure”.

Specifically, it represents the pressure exerted by a liquid or gas of 1 Pound value on the wall of a duct or the bottom of a tank that has an area of 1 Square Inch.
In the international standard of measurement, 1 PSI = 1 yard of water (27.7 Inches).

  • Pressure is said to be absolute (PSIA) if and only if it is measured, without reference to any point other than itself. For example, the measured atmospheric pressure is 14.7 PSIA.
  • When the pressure is referenced to the atmosphere, it is called the gauge pressure (PSIG). For example, the pressure of water relative to the air, etc.
At present, all kinds of steel pipes are produced and want to supply to the market. All must have PSI test pressure according to international standards such as ASTM, BS 1387-1985 (EN 10255), …
Or specify the withstand pressure for the user to know.
If it is to talk about this PSI in depth, it is very long and complicated. In order not to confuse you, I just leave the link here. If you want to learn more, you can click on PSI and related definitions.
Now you know that Psi is the unit that represents pressure. So what does it mean? Or is it just a representative?
Stay tuned for the answer!

What is the meaning of PSI?

Here, we will look at 2 cases, and go into the analysis of both.

  • Producer
  • End users (investors, contractors, residents, …)
What is the meaning of Psi?

First for pipe manufacturers:

  • The PSI index of the standard (the standard for steel pipe production is different for each company: ASTM, BS EN, …) is the basis that manufacturers rely on to produce steel pipes.
  • It stipulates how much pressure that steel pipe must withstand to reach the quality supplied to the market. For example, according to ASTM A53, for pipes of class F — butt weld, continuous welding, and Class A, minimum stress of 30 000 PSI must be achieved.

For design and construction contractors and investors.

  • The general contractors and investors will rely on the PSI index of the steel pipe to be able to calculate the size selection; type of pipe suitable for construction for your project.
  • The inspection units will also be easier to verify the quality of the works; calculate a reasonable construction plan.

>>> Here is a practical example for your reference (note that if you are free, watch it, I’m afraid you guys will get confused).

For example, based on the PSI of steel pipes for water supply construction

Assumption: Take the required daily water flow for a 30-meter-high building, 200 m3/day in 1 day and night. Temporarily calculate the time of water supply in the day is 5 hours. The flow through the meter for 1 hour is 40 m3/h.
Bản vẽ hệ thống cấp nước của tòa nhà
Example of building water supply drawing – Source: meeshop.vn
Calculate:
We have the formula to calculate the liquid pressure as P = d*h (Pa)
d is the specific gravity of the liquid (N/m3), d of water is 997 kg/m³ = 9 970 N/m3
h is the height of the water column (m)
P = 9 970 N/m3 * 30 m * 40 m3/h = 11 964 (kPa) = 1 735 (PSI)
Compare according to section 6.5, standard TCVN4513:1988
The speed of water flowing in the steel pipe supplying domestic water inside the house must not exceed the following values:

In main pipes and risers: from 1.5 to 2 m/s

We choose the speed of water flowing in the pipe to be 2 m/s.
Apply the following formula to calculate the pipe diameter:
D= Sqrt((4*Q)/(V*3.14))
=> D= Sqrt((4*40)/(2*3600*3.14)) = 0.084 (m) = 84 (mm)
Look up the catalog of SeAH steel pipes. We choose a pipe with size DN80, with an outer diameter of 88.9 (mm), and a thickness of 4.78 mm.
At this point, do you wonder why so many countries around the world use this Psi unit?
Here are some great reasons to give you the answer.

The reason why countries have to use the same PSI unit to represent pressure

In the old days, standard units of measurement such as Psi, Kpa, etc. could only be applied to a community or a small area.
At that time each region developed its own standards for length, area, volume, mass, and pressure; to serve a particular field of use.
For example meters (m) and Inches (in) to measure length, Kilograms (Kg) and Pounds (lbs) to measure weight, etc.
Therefore, the trade in goods between regions, regions, and countries faces many difficulties. Typically, companies that want to import iPhones from Apple must change VND to USD.
What is Psi used in general?
In the face of the continuous development of the economy and the need for commercialization globally.
Requires measurement units to be standardized and uniform to facilitate trade.
Initially, PSI was just a unit of pressure measurement in some western countries such as the US and the UK, …
Trụ sở tổ chức BIPM
Headquarters International Bureau of Weights and Measures BIPM

It was not until 1875 that an intergovernmental organization for weighing and measuring was established (abbreviated BIPM). The BIPM organization includes:

  • Delegates of the Government of Member States
  • Observers from Associations around the world
And in 1960, the 11th General Conference on Weights and Measures (CGPM) officially ratified the International System of Units, commonly known as “SI”. Including the pressure unit PSI.
Back to the iPhone buying example above. As you can see we have to change from Vietnamese Dong to US Dollar.
What about Psi units? Now I don’t want to use the Psi unit but I want to use the Kpa unit, what should I do?
Then this next part will be what you need!

PSI unit conversion value with other units

After days of tinkering, diving into a pile of information online. Then Tiger Steel summarized the conversion value between the units as follows:
Pressure unit conversion table
Bảng quy đổi giá trị các đơn vị đo áp suất
Table to convert the value of pressure measurement units
Or you can also directly Copy the values below:
  • 1 Psi = 6.894,76 Pa
  • 1 Psi = 68,948×10−3 Bar
  • 1 Psi = 70,307×10−3 at
  • 1 Psi = 68,046×10−3 atm
  • 1 Psi = 51,715 Torr
To verify whether the above value is correct or not, you can go to the Convertworld site, then select the pressure field to convert in turn. This is a site that TIger Steel often uses to convert the value and its accuracy is very high.

A small gift for you for reading this far

In the process that Tiger Steel searches and collects information; You can find some valuable documents on pipeline construction.
Interested readers can click on each link I put below.

Extremely valuable gift compiled by Tiger Steel Document AISI standard steel grade

Hopefully after reading this article, you. The person who is sitting in front of the screen will no longer be confused by the disparate information.
Maybe what I share here will have shortcomings. So if you think you need to add anything, just call Tiger Steel for corrections!
Our hotline:

Leave a Reply

Your email address will not be published. Required fields are marked *