Table 2.2 lists the submerged weight of the PLEM’s support frame.

Figure 2.1 Overall layout of PLEM structure and piping; location of Centre of Gravity (CG)

Table 2.1

PLEM System Design Submerged Weight

Structure Design Submerged Weight (tonne)

PLEM Structure only 71.3

PLEM Support Frame 7.13

PLEM with Support Frame only 77.43

PLEM with Support Frame and PLR 88.35

Table 2.2

PLEM Structure Design Weight and CoG Summary

Structure Design Submerged Weight (tonne) Centre of Gravity

X (m) Y (m) Z (m)

PLEM Structure only 71.3 9.13 1.72 1.53

2.2.2 Overall PLEM Structure Stability

The factors of safety against overturning and sliding are shown in Table 2.3.

Table 2.3

PLEM Structure Design Weight and CoG Summary

Condition

Factor of Safety

Overturning due to PLET Loads 5.6

Overturning due to GIM and PLR loads 7.2

Sliding 2.3

These factors are in excess of the minimum requirements of 2 (overturning) and 1.5 (sliding) as defined by API RP 2A.

2.2.3 Member Stresses

The stress distribution in the PLEM and PLEM support frame is shown in figure 2.2 below. The maximum Von Mises stress of only 31.9 MPa occurs in the top member E1-R1 (member naming scheme is depicted in figure 3.6), at edge H1. The PLEM bends about the Y-axis at its midpoint (edge H1) due to the tie-in loads applied at both ends of the PLEM.

Figure 2.2 Stress distributions in the PLEM and PLEM support frame.

Members with the maximum combined unity stress check based on AISC-ASD are listed in table 2.4. Calculation details are listed in Appendix A.

Table 2.4Combined Unity Stress Check as per AISC-ASD

PLEM PLEM SUPPOR T FRAME

Criteria Member E1-H1 Member H1-M1 Member H1-H2 Member CC3-EE3

Von Mises Stress (MPa) 24.9 31.9 28.8 16.6

Allowable Von Mises Stress (MPa) 163.68 163.68 163.88 163.88

Unity Check 0.15 0.19 0.18 0.10

Bending Stress (Major) (MPa) 7.73 10.0 -14.5 16.0

Allowable Bending Stress (Major) (MPa) 163.68 163.68 163.88 163.88

Unity Check 0.05 0.06