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Calculation of the degree of danger of defects

The following methods for calculating the severity of defects are available in the pipeline_csv.integrity library module.

method ASME B31G

Usage

The depth of defects will be specified in hundredths of a millimeter.

from pipeline_csv.oegiv import Row as BaseRow
from pipeline_csv.csvfile.row import Depth

class Row(BaseRow):
    """Row with mm depth."""

    depth_units = Depth.HundredthsOfMillimeter

The pipe has a diameter of 1420 mm a length of 11.2 meters, and a wall thickness of 16 mm.

from pipeline_csv.csvfile import Stream
from pipeline_csv.csvfile.tubes import Tube

pipe = Tube(Row.as_weld(10), Stream(diameter=1420), None)
pipe.length = 11200
pipe.thick_mm = 16

Pipe material.

from pipeline_csv.integrity.material import PipeMaterial

material = PipeMaterial(
  "Steel",
  295,  # yield strength, MPa
  smts=420  # tensile strength, MPa
)

Metal loss defect (internal corrosion) with a specified position on the pipe and a given depth.

from pipeline_csv import DefektSide
from pipeline_csv.orientation import Orientation
from pipeline_csv.oegiv import TypeDefekt

pipe.add_object(
  Row.as_defekt(
    1000,  # the defect starts at a distance of 1 meter from the beginning of the pipe
    TypeDefekt.CORROZ,
    DefektSide.INSIDE,
    100,  # defect length 100 mm
    10,  # defect width 10 mm
    str(1 * 100),  # defect depth 1 mm
    # around the circumference of the pipe, the defect begins at 10 minutes of arc from the top point of the pipe
    Orientation.from_minutes(10),
    # the size of the defect along the circumference is 20 arc minutes
    Orientation.from_minutes(10 + 20),
    None,  # MPoint orient
    None,  # MPoint dist
    ''  # comment
  )
)
defect = pipe.defects[-1]

Context for calculating the degree of defect hazard using the ASME B31G method at a pressure of 7 MPa.

from pipeline_csv.integrity.method.asme.b31g_2012 import Context

asme = Context(defect, material, 7.0)

The depth of the defect is less than 10% of the pipe wall thickness, the calculated ERF of the defect is less than 1, there is no danger.

assert defect.depth_mm == 1
assert pipe.thick_mm == 16
assert 0.94 < asme.erf() < 0.97
assert asme.years() > 1

For very low pressure cases, repair is never required (special value REPAIR_NOT_REQUIRED=777).

asme.maop = 0.01
assert asme.years() == asme.REPAIR_NOT_REQUIRED

A defect depth of 50% of the pipe wall thickness requires repair at the specified working pressure in the pipe (ERF> 1).

asme.maop = 20
defect.depth_mm = 8
defect.length = 200
assert asme.years() == 0
assert asme.erf() > 1

When the operating pressure is reduced to a safe value, the defect does not require repair.

asme.maop = asme.safe_pressure - 0.1

assert asme.years() > 0
assert asme.erf() < 1

After the calculation is completed, the asme.explain() method will return an explanation of the calculation in text form.

Calculate ERF by ASME B31G 2012 classic.
Calculate failure stress level by the classic way.
Parameter Sflow = 1.1 * material_smys.
Sflow = 1.1 * 52000 = 57200.0.
Parameter Z = length^2 / (diameter * wallthickness).
Z = 30^2 / (56 * 0.63) = 25.51.
Parameter Z = 25.51 > 20.
Failure stress level = Sflow * (1 - depth / wallthickness).
stress_fail = 57200.0 * (1 - 0.31 / 0.63) = 29053.968.
Failure pressure = 2 * stress_fail * wallthickness / diameter.
press_fail = 2 * 29053.968 * 0.63 / 56 = 653.714.
ERF = pipe_maop / press_fail.
ERF = 500 / 653.714 = 0.765

Repair is not required at the moment, calculate the time before repair.
With corrosion rate 0.016 mm/year, pipe wall 0.63 and depth 0.31 a through hole is formed after years: 21.
Calculating the year in which the corrosion growth of the defect will require repair.
Years: 4 ERF: 0.952.
Years: 5 ERF: 1.014.
Defect will require repair after years: 4.

Examples

Living version of online calculator example, that use this library, can be found here. The source code of this example placed in this repo in example dir.

The source code for the example for running the online calculator on a local computer is contained in the localhost directory of the repository.