Understanding pressure and temperature – Frequent term for plant engineers –

If you are a plant engineer, assume that you would hear conversations almost every day regarding temperature and pressure.

For example,
”What is the piping design pressure and temperature？“
“How much pressure is required for the sootblower steam？”
“How much difference is there between the operation temperature and design temperature ？”
“Pressure from the construction department is so high.”
The last one is half a joke but one of a reason and motivations that plant designers work hard.

 Why so important and frequently comes out ？

The reason is because it is the basis to design material and thickness of boiler tubes , piping or ducting. Also for piping, it is the basis to decide Valve / flange ratings.

If you cannot tell what temperature the product will become and how much pressure it will receive, it is impossible to design it. 

What range of temperature and pressure is handled at power plant boilers ？

 In power plant boilers, fluid (steam, water, gas, air) are handled at following ranges.

・Water / steam pressure…0 MPa 〜 23 MPa
・Steam Temperature… 300℃（Feed Water） 〜 650 ℃ (Reheater Steam)
・Gas Temperature…80℃（Chimney） 〜 1600 ℃ (Furnace)

Very high pressure and temperature is handled that you would never see or experience during daily life. The steam for boilers are maintained high pressure and temperature for better thermal efficiency. However, it makes the structure design of boilers special and difficult. As you can imagine, at these severe conditions, it requires cautious to design tubes, piping and attachments etc., otherwise it can easily cause failure which may lead to catastrophic result.

Comparing with daily life temperatue and pressure

Comparing with daily life stuff would be easy to imagine how high the pressure and temperature of the fluid handled in a boiler.

Pressure (all value in gauge pressure)

• Pressure cooker… 80～120 kPa
• Firefighting discharge water… 0.7 MPa
• Soda maker CO2 cylinder… 5.9 MPa
• Steam cleaner machine … 0.5 MPa
• 50kg lady stepping on with high heels… 5 MPa
• Depth of 10 m inside water… 0.1 MPa (+ 0.1 MPa for every 10m deeper)

Temperature

• Steam at atmospheric pressure…100 ℃
• Pressure cooker…120 ℃
• Bottom of a pot when heating by a gas stove in kitchen…230 ℃
• Gas stove flame（In Japan LPG or LNG)…1700～1900 ℃

What do you think by comparing with daily life temperature and pressure ? Even in daily life, you can imagine that 0.7 MPa firefighting discharge water pressure is quite strong. And wow, high heels can be a very powerful weapon.

You can be easily burned by a heated pot that is 230℃. Can you imagine what will happen to you if you touch a 650℃ steel tube in a boiler ? Don’t want to imagine.

Even in stuff surrounded by daily life, it can cause severe damage to our bodies.

Need to imagine how catasrophic it can be if you don’t handle and design plant products properly.

As an Engineer, it is required to imagine physically from the numbers on papers. That sense would help to design correctly and feel something is wrong when it is wrong.

Personally, I heard a case in my previous company that when condcuting a hydrostatic pressure test for a piping the hydrostatic test cap (more than 100 kg) blowed out. Fortunately, it did not hit any human. However, this shows what high pressure fluid can cause if inappropriate design or manufacture is occured.