×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Conversion between Nm3/hr to Sm3/hr and vice versa

## Conversion between Nm3/hr to Sm3/hr and vice versa

(OP)
Hi all,

I am just curious when do you use Nm3/hr and Sm3/hr. How do you convert between the two units?

Thank you.

Chemprocess

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

See previous posts on this topic on Eng Tips

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Unfortunately neither Nm3 or Sm3 (or Standard cubic feet for that matter) are complete definitions in themselves. It is essential to know the temperature and pressure conditions that the author believed were "Normal" or "Standard".

Once you have the temperature and pressure references it is a simple matter to do the conversion.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Messrs tickle and katmar are both right.

Some experts consider NTP and STP -reference conditions- as equivalent terms. Notwithstanding their expertise, they should clearly indicate T and P to enable making conversions to differing T or P values.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

chemprocess,

The importance of the defining T & P values are very important. I had one experience where there was a dispute on the amount of hydrogen exported to another plant from one plant in an integrated petrochemical complex. It turns out that one plant was designed by a European company and the other was designed by a Japanese company. They had their definitions of  Normal (NTP) and Standard (STP) conditions in reverse (Don't ask me who got it right!). This led to inconsistent basis for calculating the mass of hydrogen transferred from one plant to the other.

It is easy to assume that there is an internationally accepted 'standard' for STP or NTP, but this is'nt so. Looking back at your university text books may not help either in this case. You must refer to the design basis of your respective plants.

RR

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

What I have experienced so far Nm3/hr is the volume flow considered at 0°C and 1 bar (absolute).
Sm3/hr is the flow taken at 15°C and 1 atm (1,013 barA).
However, the 15°C is sometimes subjected to dicussion: 20°C is taken as well.

Conversion can easily be made by using (P*V)/T = C

Regards, Kingsss

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Just to make your life easier: an extensive thread on this topic can be found on Thread378-97454

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

The standard conditions are as follows:

Temp.: 15 degr C, Press.: 1.01325 bara

THe normal conditions are as follows:

Temp.: 0 degr C, Press.: 1.01325 bara

How to convert between the two in obvious.

regards

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Homayun,

Those may be your definitions of Standard and Normal but there are many others.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

No katmar,

These are to my knowledge the widely used conditions, I haven't invented them! So I don't know what you are talking about.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Homayun, sorry to tell you that standard and normal conditions have various definitions as katmar says. I suggest you visit the following threads to get an idea of the situation:

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Homayun,

I must admit that it was only relatively recently that I discovered that Normal is not a universal definition. The IUPAC (International Union of Pure and Applied Chemists), which is a well respected organisation, defines it as 100 kPa. Most older books use 101.325 kPa.

Standard conditions are most frequently used in the USA. {/Bait on} I don't want to be rude, but until a few years ago most engineers there didn't know what degrees C were, so they would not have made their definition in those units. I won't tell you what most American engineers think a bar is, but as a hint, the Absolut part is associated with Vodka.{/Bait off}

The bottom line is - the gas conditions need to be defined for every calculation, contract etc where they are used.

regards
Katmar

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Katmar is right. I know atleast three temperature conditions for STP with 0(no..not NTP), 15 and 160C, in use.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Adding to quark's list, at least until a few years ago:

The American Gas Association: 60oF (15 5/9oC) and 30 inches (762 mm) of mercury.

The Compressed Gas Institute: 20oC (68oF) and 1 atmosphere.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

But this is not good to have different conditions with same name: standard  / normal conditions ! This makes things complicated I would say at least, and in some cases even dangerous.

### RE: Conversion between Nm3/hr to Sm3/hr and vice versa

Corect !! That's the reason for the obligation to clearly state what are the P, T conditions every time to avoid confusion.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!