'''
This module provides classes and functions for calculating DNV pipeline limit states and material
properties.
**Features:**
- The `DNVGeneral` class implements calculations for temperature derating, yield and tensile
strength, and characteristic material burst strength, supporting both scalar and array-based
inputs.
- The `DNVLimitStates` class extends `DNVGeneral` and provides burst pressure calculations for
pipelines according to DNV standards.
- Designed for use in subsea pipeline and riser engineering, but general enough for any DNV-based
pipeline property calculations.
All calculations are vectorized using NumPy for efficiency and flexibility.
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'''
import numpy as np
[docs]
class DNVGeneral: # pylint: disable=too-many-instance-attributes, too-many-arguments
"""
Base class for DNV pipeline limit state calculations. Provides methods for temperature
derating, yield and tensile strength, and characteristic material burst strength,
supporting both scalar and array-based inputs.
Parameters
----------
outer_diameter : float or array-like, optional
The outer diameter of the pipeline.
corroded_wall_thickness : float or array-like, optional
The corroded wall thickness of the pipeline.
material : float or array-like, optional
Material types: 1 for 'CMn' or '13CR', 2 for '22Cr' or '25CR'.
smys : float or array-like, optional
Specified minimum yield strengths.
smts : float or array-like, optional
Specified minimum tensile strengths.
temperature : float or array-like, optional
Temperatures for calculations.
material_strength_factor : float or array-like, optional
Material strength factor.
Notes
-----
All calculations are vectorized using NumPy for efficiency and flexibility.
"""
def __init__(
self,
*,
outer_diameter=0.0,
corroded_wall_thickness=0.0,
material=None,
smys=0.0,
smts=0.0,
temperature=0.0,
material_strength_factor=0.0
):
"""
Initialize with material, strength, and geometric properties.
"""
self.outer_diameter = np.asarray(outer_diameter, dtype = float)
self.corroded_wall_thickness = np.asarray(corroded_wall_thickness, dtype = float)
self.material = np.asarray(material, dtype = float)
self.smys = np.asarray(smys, dtype = float)
self.smts = np.asarray(smts, dtype = float)
self.temperature = np.asarray(temperature, dtype = float)
self.material_strength_factor = np.asarray(material_strength_factor, dtype = float)
[docs]
def temperature_derating_stress(self):
"""
Calculate the temperature derating stress of a material.
Returns
-------
temperature_derated_stress : np.ndarray
The derating stress values for the given materials and temperatures.
Raises
------
ValueError
If a material is not supported.
Examples
--------
>>> materials = np.array([1, 1, 2, 2])
>>> temperatures = np.array([80.0, 110.0, 80.0, 110.0])
>>> dnv = DNVGeneral(
... material=materials,
... temperature=temperatures
... )
>>> dnv.temperature_derating_stress()
array([18000000., 34000000., 70000000., 95000000.])
"""
derating_array = np.empty(0)
for mat, temp in zip(self.material, self.temperature):
if mat == 1:
derating_value = np.interp(temp,
[50.0, 100.0, 200.0],
[0.0, 30.0E+06, 70.0E+06])
elif mat == 2:
derating_value = np.interp(temp,
[20.0, 50.0, 100.0, 200.0],
[0.0, 40.0E+06, 90.0E+06, 140.0E+06])
else:
raise ValueError('Material not supported')
derating_array = np.append(derating_array, derating_value)
return derating_array
[docs]
def yield_stress(self):
"""
Calculate the yield stress of a material.
Returns
-------
yield_stress : np.ndarray
The yield stress values of the materials at the given temperatures and strength factor.
Examples
--------
>>> materials = np.array([1, 1, 2, 2])
>>> smys = np.array([450.0E+06, 450.0E+06, 550.0E+06, 550.0E+06])
>>> temperatures = np.array([80.0, 110.0, 80.0, 110.0])
>>> material_strength_factor = np.array([0.96, 0.96, 0.96, 0.96])
>>> dnv = DNVGeneral(
... material=materials,
... smys=smys,
... temperature=temperatures,
... material_strength_factor=material_strength_factor
... )
>>> dnv.yield_stress()
array([4.1472e+08, 3.9936e+08, 4.6080e+08, 4.3680e+08])
"""
derating_value = self.temperature_derating_stress()
return (self.smys - derating_value) * self.material_strength_factor
[docs]
def tensile_strength(self):
"""
Calculate the tensile strength of a material.
Returns
-------
tensile_strength : np.ndarray
The tensile strength values of the materials at the given
temperatures and strength factor.
Examples
--------
>>> materials = np.array([1, 1, 2, 2])
>>> smts = np.array([485.0E+06, 485.0E+06, 590.0E+06, 590.0E+06])
>>> temperatures = np.array([80.0, 110.0, 80.0, 110.0])
>>> material_strength_factor = np.array([0.96, 0.96, 0.96, 0.96])
>>> dnv = DNVGeneral(
... material=materials,
... smts=smts,
... temperature=temperatures,
... material_strength_factor=material_strength_factor
... )
>>> dnv.tensile_strength()
array([4.4832e+08, 4.3296e+08, 4.9920e+08, 4.7520e+08])
"""
derating_value = self.temperature_derating_stress()
return (self.smts - derating_value) * self.material_strength_factor
[docs]
def characteristic_material_burst_strength(self):
"""
Calculate the characteristic material burst strength.
Returns
-------
characteristic_burst_strength : np.ndarray
The characteristic material burst strength values at the given
temperatures and strength factor.
Examples
--------
>>> materials = np.array([1, 1, 2, 2])
>>> smys = np.array([450.0E+06, 450.0E+06, 550.0E+06, 550.0E+06])
>>> smts = np.array([600.0E+06, 600.0E+06, 700.0E+06, 700.0E+06])
>>> temperatures = np.array([80.0, 110.0, 80.0, 110.0])
>>> material_strength_factor = np.array([0.96, 0.96, 0.96, 0.96])
>>> dnv = DNVGeneral(
... material=materials,
... smys=smys,
... smts=smts,
... temperature=temperatures,
... material_strength_factor=material_strength_factor
... )
>>> dnv.characteristic_material_burst_strength()
array([4.1472e+08, 3.9936e+08, 4.6080e+08, 4.3680e+08])
"""
yield_stress_value = self.yield_stress()
tensile_strength_value = self.tensile_strength()
return np.minimum(yield_stress_value, tensile_strength_value / 1.15)
[docs]
class DNVLimitStates(DNVGeneral):
"""
Class for DNV pipeline burst pressure limit state calculations.
Extends `DNVGeneral` to provide burst pressure calculations for corroded pipelines
according to DNV standards, using material, geometric, and strength properties.
Parameters
----------
outer_diameter : float or array-like, optional
The outer diameter of the pipeline.
corroded_wall_thickness : float or array-like, optional
The corroded wall thickness of the pipeline.
material : float or array-like, optional
Material types: 1 for 'CMn' or '13CR', 2 for '22Cr' or '25CR'.
smys : float or array-like, optional
Specified minimum yield strengths.
smts : float or array-like, optional
Specified minimum tensile strengths.
temperature : float or array-like, optional
Temperatures for calculations.
material_strength_factor : float or array-like, optional
Material strength factor.
Notes
-----
All parameters are passed to the parent class `DNVGeneral`.
"""
[docs]
def burst_pressure(self):
"""
Calculate the burst pressure of a pipeline.
Returns
-------
burst_pressure : np.ndarray
The burst pressure values of the pipeline.
Raises
------
ValueError
If a material is not supported.
Examples
--------
>>> outer_diameter = np.array([0.2731, 0.3239, 0.2731, 0.3239])
>>> corroded_wall_thickness = np.array([0.0097, 0.0129, 0.0097, 0.0129])
>>> materials = np.array([1, 1, 2, 2])
>>> smys = np.array([450.0E+06, 450.0E+06, 550.0E+06, 550.0E+06])
>>> smts = np.array([600.0E+06, 600.0E+06, 700.0E+06, 700.0E+06])
>>> temperatures = np.array([80.0, 110.0, 80.0, 110.0])
>>> material_strength_factor = np.array([0.96, 0.96, 0.96, 0.96])
>>> dnv = DNVLimitStates(
... outer_diameter=outer_diameter,
... corroded_wall_thickness=corroded_wall_thickness,
... material=materials,
... smys=smys,
... smts=smts,
... temperature=temperatures,
... material_strength_factor=material_strength_factor
... )
>>> dnv.burst_pressure()
array([35270393.70222808, 38255444.18258572, 39189326.33580898, 41841892.07470313])
"""
fcb = self.characteristic_material_burst_strength()
return (
(2.0 * self.corroded_wall_thickness)
/ (self.outer_diameter - self.corroded_wall_thickness)
* fcb * 2.0 / np.sqrt(3.0)
)
