# Economic Superiority of PIP Slip Joint Compared to Conventional Tubular Joints
## 2 Methodology
### Data Collection  
To ensure a comprehensive and standardized comparison among different joint types, data were collected from a variety of credible sources. These included industry reports on offshore wind energy projects, manufacturer specifications for joint materials and fabrication, historical data on installation and maintenance costs, and peer-reviewed research evaluating the structural and economic performance of grouoted, bolted flange, and PIP slip joints.  
The support structure cost data were obtained from the references listed in Section 2.1, which provide robust and previously validated estimates. The structural designs were developed according to a prior study on PIP slip joints, as well as NORSOK and Eurocode standards, from which accurate dimensions were derived [19; 50; 51]. These dimensions enabled detailed material quantity estimations, which in turn contributed to the calculation of initial material and fabrication costs.  
Several assumptions were made to standardize the comparative analysis. All joint types were assumed to meet the same structural performance criteria. Installation scenarios were modeled under moderate offshore conditions. The lifecycle of the project  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Parameters** & **Symbol** & **Value** & **Unit** \\ \hline Inner Dia of Inner Pile & \(d_{I}\) & 9780 & mm \\ Outer dia of inner pile & \(d_{O}\) & 10,000 & mm \\ Inner dia of outer pile & \(D_{I}\) & 10,000 & mm \\ Outer dia of outer pile & \(D_{O}\) & 10,220 & mm \\ Thickness of each ring stopper & \(t\) & 200 & mm \\ Width of each ring stopper & \(l\) & 190 & mm \\ Overlapping length & \(L_{o}\) & 20,000 & mm \\ \hline \hline \end{tabular}
\end{table}
Table 4: Dimensions of PIP slip joint.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Parameters** & **Symbol** & **Value** & **Unit** \\ \hline Outside Diameter of the Pile & \(D_{p}\) & 10,000 & mm \\ Effective grouoted connection length & \(L_{e}\) & 20,000 & mm \\ Shear key spacing & \(s\) & 600 & mm \\ Wall thickness of pile & \(tp\) & 110 & mm \\ Outside diameter of pile sleeve & \(D_{s}\) & 10,550 & mm \\ Wall thickness of transition piece & \(t_{tp}\) & 75 & mm \\ Outside diameter of grou annulus & \(D_{g}\) & 10,200 & mm \\ Thickness of grou annulus & \(t_{g}\) & 280 & mm \\ Characteristic cube strength & \(f_{CK}\) & 130 & MPa \\ Shear key height & \(h\) & 60 & mm \\ Shear key width & \(w\) & 180 & mm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Dimensions of grouot joint.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Parameters** & **Symbol** & **Value** & **Unit** \\ \hline Inner Dia & \(D_{I}\) & 9780 & mm \\ Outer dia & \(D_{O}\) & 10,000 & mm \\ Bolt c/c distance & \(s\) & 120 & mm \\ Wall thickness of pile & \(tp\) & 110 & mm \\ Grade of bolt & \(12.9\) & 12.9 \\ Diameter of each bolt & \(d\) & 56 & mm \\ Thickness of each flange & \(t_{f}\) & 200 & mm \\ Width of each flange & \(l_{f}\) & 190 & mm \\ \hline \hline \end{tabular}
\end{table}
Table 3: Dimensions of bolted flange joint.  
was fixed at 20 years, a duration that aligns with standard industry practices for offshore wind infrastructure and is commonly adopted in lifecycle cost assessments and financial feasibility studies [36; 38; 52]. This timeframe reflects the typical operational lifespan of wind turbines and associated substructures before major refurbishment or decommissioning is required. The discount rate applied in the net present value (NPV) analysis is based on prevailing financial market conditions, typically ranging between 6 and 8% for offshore energy projects, and accounts for investment risk, inflation expectations, and opportunity cost [19; 52].