What can help improve the ultimate strength of an existing offshore platform? Here is a tip that helps the structure reach a higher reserve strength and pass the target RSR. The structural Integrity (Ultimate Strength) of an offshore platform is mainly assessed by performing a nonlinear pushover analysis (Both SACS and USFOS can perform the analysis, I would prefer USFOS). Generally, a SACS model is available for an existing platform. This SACS model is converted to USFOS model to establish a nonlinear pushover analysis. As a normal practice, what has been used as “Yield Strength” in SACS models for steel material is “Nominal Yield Strength” which is the best for static design and re-analysis. However, when it comes to “Integrity Assessment” and nonlinear analysis to estimate the ultimate capacity/reserve strength of an offshore platform, API RP 2 SIM allows using “Mean Yield Strength” instead of “Nominal Yield Strength”. In more accurate words, when adequate data is available, the actual (coupon test or mill certification) or mean yield strength may be used instead of nominal yield strength. Be careful, “mean yield strength” should not be used when it is greater than “actual strength”. As per API RP 2SIM, the mean yield strength for 248 MPa (36 ksi) steel is estimated to be 276 MPa (40 ksi) to 317 MPa (46 ksi), with 296 MPa (43 ksi) being a reasonable average. #StructuralIntegrityAssessment #OffshorePlatform #PushoverAnalysis #APIRP2SIM #NauticMiddleEast
Hi sir, which kind of softwares did you use to analyze and designe of these type of structures?
In checking the target RSR, consideration should also be given to predominant wave direction.
Right, I had this situation of low RSR from Non- predominant wave direction but after discussion with customer, it was decided to consider RSR of predominant wave direction , in our case luckily we got high RSR from predominant direction & were safe.
Surprisingly API SIM does not provide any guides on SMYS for high strength steel i.e. Fy=345MPa & above since these are common nowadays. Any leads?
Using the mean yield strength in non-linear analyses will provide a more accurate representation of an offshore platform's ultimate capacity. This allowed value is typically higher than the nominal strength. Adopting this change has the potential to demonstrate sufficient reserve strength without requiring upgrades.
Great method by trace materials data, find the distribution and use as basis.
Nice post regarding Assessment of existing offshore jacket
Good work!
Senior Structural Engineer at PT. Dinamika Teknik Persada (DTP)
1yGreat work sir! BTW what kind of push over load did you use in the analysis?