scope:

These Guidance Notes denote procedures for heat transfer analysis, finite element (FE) heat transfer analysis, FE thermal stress analysis, and strength evaluation for liquefied gas vessels and gas fueled ships. Liquefied gas vessels include LNG/LPG/LEG carriers, bunker ships, barges, FSRUs, and other offshore terminals. These Guidance Notes provide an overview of steady-state heat transfer analysis methodology to estimate temperature distributions and corresponding heat transfer coefficients (HTCs) of hull structures in membrane or independent-type vessels under IGC or USCG environmental conditions. USCG environmental conditions for hull material selection are also applicable for non-US flag gas carriers (IGC Code applicable vessels) operating on the navigable waters of the United States and are not applicable to gas fueled vessels (IGF Code applicable vessels).

The estimated temperature distribution in both hull and void spaces can be employed for the steel grade selection of hull structures and the boil-off rate (BOR) calculation, and for further detailed FE analyses of tank and supporting structures in independent Type B and C vessels.

For membrane-type vessels, the temperature distribution of hull structure is calculated for material grade selection and the BOR calculation.

For independent Type A vessels, the temperature distribution of hull structure is calculated for material grade selection and the BOR calculation.

For independent Type B vessels, design thermal loads for various loading cases including cooling down, partial filling, and full loading are considered together with other mechanical loads to determine stress distributions from FE stress analysis. Finally, the stress distribution is used to evaluate the strength adequacy against yielding and buckling of tank structures.

For independent Type C vessels, the detailed temperature distribution of supporting structures can be calculated to guide steel grade selection using steady-state thermal FE analysis based on estimated results. Stress distributions from FE thermal stress can be determined for strength evaluation.

Section 1, Figure 1 denotes the process for conducting heat transfer analysis, FE heat transfer analysis, FE thermal stress analysis, and strength evaluation.