Steel pipe under high external pressure

[ptaa32]

Hi,

We have a steel tube with yield limit 1000 N/mm2.
It is 250 mm long, outside diam. is 76 mm, inside diam. is 60 mm.
It is plugged at both ends.
Inside pressure is 0 (zero) and outside pressure due to submersion is 69 Mpa.

Will this be safe?
How can I calculate what pressure that would be 'catastrophic' for the pipe?

Kind regards,

Per-Tore Aasestrand
Bergen, Norway

 

[Q_Goest]

Hi Per-Tore, welcome to the board. I would use the ASME piping code to determine safe stresses on externally pressurized pipe. We had a discussion on this here:
https://www.physicsforums.com/showthread.php?t=532901
If you don't have access to the ASME BPV code, you might consider using Roark's but I always use the ASME code for this and am not familiar with how Roark's does this and I've left my copy at the office.

Edit: I'm sure there's a piping code in Europe which is equivalent to the ASME code in the US. If this is an industrial application, you will be required by law to perform the structural analysis per the applicable European code.

 

[ptaa32]

Hi,

Thanks for the tip.
It is for a research project, so there is no need for code compliance.
The cylinder will contain some instrumentation, and I only need to know if it will survive the depth. Preferably also what the margins are.

 

[Dong xianming]

Casing Pipe 139.7*9.17 , mark C-75

Who can find this casing pipe ?

 

[alphy]

Based on the given information, it is possible to calculate the maximum pressure that the steel pipe can withstand before reaching its yield limit. The yield limit of 1000 N/mm2 means that the steel can withstand a maximum stress of 1000 N per square millimeter before it starts to deform permanently.

Using the formula for hoop stress, the maximum pressure that the steel pipe can withstand before reaching its yield limit can be calculated as follows:

Maximum pressure = (yield limit * inner diameter) / (outer diameter - inner diameter)

Substituting the given values, we get:

Maximum pressure = (1000 N/mm2 * 60 mm) / (76 mm - 60 mm) = 1250 N/mm2

This means that the steel pipe can withstand a maximum pressure of 1250 N/mm2 before it starts to deform permanently.

In the given scenario, the outside pressure due to submersion is 69 MPa, which is equivalent to 69,000,000 N/m2. This is well below the maximum pressure that the steel pipe can withstand, indicating that it should be safe under these conditions.

To calculate the pressure that would be 'catastrophic' for the pipe, we would need to know the ultimate tensile strength of the steel used in the pipe. This is the maximum stress that the steel can withstand before it fractures. Once we have this value, we can use the same formula as above to calculate the maximum pressure that the steel pipe can withstand before it reaches its ultimate tensile strength. Any pressure beyond this value would be considered 'catastrophic' for the pipe.

In conclusion, based on the given information, the steel pipe should be safe under the specified conditions. However, it is important to consider the ultimate tensile strength of the steel to determine the maximum pressure that the pipe can withstand before it reaches a catastrophic failure.