Subject
Whilst it is perfectly acceptable to define fluid flow in a pipe using classical theory, it remains a theoretical calculation and includes no margin for error and takes no account of unknown variables in practical applications such as bends & elbows.
The world’s most recognised authority on pipe and pipeline design and their specification is API and their related recommended practice is 14E
(RP 1111), which includes safety factors and limitations for their use in the oil and gas industry.
The principal limitation imposed in this recommended practice is fluid velocity, which is responsible for erosion of the pipe wall. As most industrial pipes and pipelines receive annual inspections, it is important that the expected erosion rate does not exceed acceptable levels between inspections. RP 14E also takes into consideration multiphase fluid flow (gas and/or liquid), which is particularly damaging and unpredictable with regard to erosion.
Calculator
APIpe is an alternative to CalQlata's Pipe Flow calculator incorporating the suggestions and recommendations proposed by the American Petroleum Institute for hydrocarbon transportation.
APIpe calculates the pressure drop, flow rate, velocity and velocity limitations of liquids, gases and 2phase fluids according to RP 14E
Whilst APIpe only calculates average fluid velocities, it also sizes your pipe wall according to API with no need for further safety margins.
This pipe flow calculator works with specific ‘Imperial’ units, which best relate to RP 14E
Note: This calculator has not been officially endorsed by the API. It is CalQlata’s interpretation of the recommended practice
For help using this calculator see Technical Help
Pipe Flow Calculator for API Criteria  Options
Liquid
APIpe calculates the liquid flow in pipes along with expected pressure drop, average velocity of the liquid and its limitations for ‘flashing ahead’ (too fast) and solid deposition (too slow) and calculates the minimum recommended wall thickness for your pipe.
You enter: 
and the pipe flow calculator for API criteria will provide: 


Average velocity

Specific gravity

Reynolds number

Pressure drop

Wall thickness

Moody friction factor

Gas
APIpe calculates the gas flow in pipes along with expected pressure drop, average velocity of the gas and tells you if the expected pressure drop is excessive, which can negatively affect performance and system costs. This calculation option also calculates the minimum recommended wall thickness for your pipe.
You enter: 
and the pipe flow calculator for API criteria will provide: 


Average velocity

Specific gravity

Reynolds number

Pressure drop

Wall thickness

Moody friction factor

2Phase
APIpe calculates the twophase fluid flow in pipes along with average velocity of the fluid, the expected pressure drop and also tells you if the flow rate is sufficiently low to avoid erosion and sufficiently high to avoid solid deposition. This calculation option also calculates the minimum recommended wall thickness for your pipe.
You enter: 
and the pipe flow calculator for API criteria will provide: 


Composite density

Maximum velocity

Minimum area

Minimum diameter

Average velocity

Liquid flow rate

Pressure drop

Wall thickness

Check minimum system requirements