Default Hole Size per DM

Updated on 09 Aug 2024
1 Minute to read
Contributors

Print
Dark
Light
PDF

Article summary

Did you find this summary helpful?

Thank you for your feedback

The following approach should be used for an S-RBI People Detail Consequence Assessment (Step 8):

For each DM, assess the DM as either a leak or a rupture.
For all rupture cases, use full line size as the failure size.
For all leak cases, use a standard hole size for the Consequence Assessment.
In addition, for all leak cases, evaluate whether the failure size should be increased to a rupture case, based on the material properties (using toughness exemption curves provided in API-579 brittle fracture assessment module) to account for the potential of unstable defect growth.

Experience has shown that limiting the number of hole sizes, allows for an analysis that is manageable and yet still reflects the range of possible outcomes. This approach also provides reproducibility and consistency between studies.

Default (equivalent) hole size suggestions for release rate calculations for the following DM caused failures:

Degradation Mechanism	Default Hole Diameter	Comments
Alcohol SCC	6 mm / 0.25 in	Cracks are tight and filled with corrosion products.
Amine SCC	6 mm / 0.25 in
Brittle Fracture	Rupture	Full inventory
Carbonate SCC	6 mm / 0.25 in	Leaks will start small but rapidly progress to large releases.
Caustic SCC	6 mm / 0.25 in	Leaks will start small but rapidly progress to large releases.
Chloride SCC – internal	3 mm / 0.125 in	Very tight cracking or sweating
Chloride SCC – external	3 mm / 0.125 in	Very tight cracking or sweating
Corrosion - General	12.5 mm / 0.5 in	For low pressure services (< 5 bar or 74 psi), the hole size may be reduced depending upon the extent of the corrosion.
Corrosion – Localized in gas service	3 mm / 0.125 in
Corrosion – Localized in liquid service	6 mm / 0.25 in
Corrosion Under Insulation (CUI)	12.5 mm / 0.5 in	For all cases
Fatigue - Vibration	6 mm / 0.25 in
High Temperature Hydrogen Attack (HTHA)	Rupture	Full inventory; welds or highly stressed areas are more likely to have damage.
Hydrogen Induced Cracking (HIC) SCC	None	HIC cracking an indication of hydrogen activity; leakage occurs if the cracks join up as SOHIC.
Polythionic Acid (PTA) SCC	3 mm / 0.125 in	Very tight cracking; seeping around grain boundaries or sweating.
Stress Oriented Hydrogen Induced Cracking (SOHIC) SCC	6 mm / 0.25 in	Tight cracking in weld heat affected zones parallel to the weld; weeping leaks in low pressure services; higher pressure services may have the potential for rupture.
Sulfide SCC	6 mm / 0.25 in	Tight transverse cracking across welds result in weeping leaks.

Was this helpful? Click to add feedback comments

What's Next

Release Rate Calculations