﻿ 考虑腐蚀影响的老旧FPSO船体总纵强度研究
 舰船科学技术  2018, Vol. 40 Issue (3): 83-88 PDF

Research on longitudinal strength of old FPSO considering the influence of corrosion
LI Gang, YI Cong, WANG Zhao-yang, FAN Mo, LI Da
CNOOC Research Institute, Beijing 100028, China
Abstract: In this paper, an FPSO that has operated nearly 20 years in Bohai bay was studied. The hydrostatic load and frequency wave load of the FPSO were respectively calculated by MOSES and SESAM, and then the longitudinal load of the hull would be obtained. The section modulus considering corrosion of the hull was calculated based on the regulation on corrosion rate in the "Rules for the Classification and Construction of Offshore Floating Units". Then the longitudinal strength of the FPSO after continuing to operate different years was checked based on the "Rules and Regulations for the Construction and Classification of Sea Going Steel Ships", and the suggestion for enhancing the structural strength was also be proposed. The code check results show that the longitudinal strength of this FPSO can man meet standard requirements.
Key words: old FPSO     longitudinal load     corrosion     section modulus     longitudinal strength
0 引　言

FPSO（浮式生产储卸油装置）作为集生产处理、储存外输及生活、动力供应等多功能于一体的综合大型海上生产设施，已逐渐成为海上石油资源开发中不可或缺的重要装备[12]。然而，FPSO在海上运营过程中长期处于复杂的海洋环境中，其船体和舱内的构件通常会发生较为严重的腐蚀，从而将导致船体结构强度尤其是总纵强度降低[34]。因此，对老旧FPSO进行考虑腐蚀影响的总纵强度分析，对保证其安全性具有极其重要的意义[5]

1 船体总纵外载荷计算

1.1 静水载荷计算

 图 1 静水载荷计算模型 Fig. 1 Hydrostatic load calculation model

 图 2 满载时的静水剪力和弯矩沿船长分布 Fig. 2 Distribution of hydrostatic shear force and bending moment along ship length in full load condition

 图 3 压载时的静水剪力和弯矩沿船长分布 Fig. 3 Distribution of hydrostatic shear force and bending moment along ship length in ballast condition

1.2 波浪载荷计算

 图 4 波浪载荷计算流程图 Fig. 4 Flow chart of wave load calculation
1.2.1 计算模型及工况

 图 5 船体有限元模型 Fig. 5 Finite element model of hull wet surface

 图 6 质量模型 Fig. 6 Mass model

1.2.2 波浪载荷直接预报

1）短期预报

 $S(\omega ) = \alpha {g^2}{\omega _{{p}}}^{ - 5}\exp \left[ { - \frac{5}{4}{{(\frac{\omega }{{{\omega _p}}})}^{ - 4}}} \right]{\gamma ^{\exp \left[ { - \frac{1}{{2{\sigma ^2}}}{{(\frac{{\omega - {\omega _p}}}{{{\omega _{{p}}}}})}^2}} \right]}}\text{，}$ (1)

 $\left\{ \begin{gathered} \gamma {{ = }}5{{ }}{T_P}/\sqrt {{H_S}} \leqslant 3.6 \text{，}\hfill \\ \gamma = \exp (5.75 - \frac{{1.15{T_P}}}{{\sqrt {{H_S}} }}){{ 3}}{{.6 < }}{T_P}/\sqrt {{H_S}} < 5 \text{，}\hfill \\ \gamma = 1{{ }}{T_P}/\sqrt {{H_S}} \geqslant 5 \text{。}\hfill \\ \end{gathered} \right.$ (2)

2）长期预报

3）直接预报结果

 图 7 波浪剪力直接预报值沿船长分布曲线 Fig. 7 Distribution curve of wave shear force direct forecast value along ship length

 图 8 波浪弯矩直接预报值沿船长分布曲线 Fig. 8 Distribution curve of wave bending moment direct forecast value along ship length
1.2.3 总纵外载荷

 $\left\{ \begin{gathered} N( + ) = {N_S} + {N_V}( + ) \text{，}\hfill \\ N( - ) = {N_S} + {N_V}( - ) \text{，}\hfill \\ M( + ) = {M_S} + {M_V}( + ) \hfill \text{，}\\ M( - ) = {M_S} + {M_V}( - ) \hfill \text{。}\\ \end{gathered} \right.$ (3)

 图 9 总纵剪力沿船长分布曲线 Fig. 9 Distribution curve of longitudinal shear force along ship length

 图 10 总纵弯矩沿船长分布曲线 Fig. 10 Distribution curve of longitudinal bending moment along ship length

2 考虑腐蚀影响的船体总纵强度分析 2.1 船体剩余剖面模数 2.1.1 构件腐蚀量计算方法

 ${t_{corr}} = {N_r}({t_{c1}} + {t_{c2}})\text{，}$ (4)

2.1.2 剩余剖面模数计算方法

 $\left\{ \begin{gathered} A = \sum {{A_i}} {{ }} \text{，}\hfill \\ B = \sum {{A_i}{Z_i}{{ }}} \text{，}\hfill \\ C = \sum ( {A_i}{Z_i}^2 + {i_0}){{ }} \hfill \text{。}\\ \end{gathered} \right.$ (5)

 $\varepsilon = \frac{B}{A}{{ }}\text{。}$ (6)

 $I = 2\left( {C - {\varepsilon ^2}A} \right){{ = }}2(C - \frac{{{B^2}}}{A}){{ }}\text{。}$ (7)

 ${Z_i}^\prime = {Z_i} - \varepsilon \text{，}$ (8)

 $\left\{ \begin{gathered} {W_d} = I/{Z_{^d}}^\prime = ({Z_d} - \varepsilon ) \hfill \text{，}\\ {W_b} = I/{Z_{^b}}^\prime = ({Z_b} - \varepsilon ) \hfill \text{。}\\ \end{gathered} \right.$ (9)

2.2 船体总纵强度校核 2.2.1 总纵弯曲强度

 $\sigma ( \pm ) \leqslant \left[ \sigma \right]\text{，}$ (10)

 $\sigma ( \pm ) = \frac{{\left| {M( \pm )} \right|}}{W}\text{，}$ (11)

2.2.1 总纵剪切强度

 $\tau ( \pm ) \leqslant \left[ \tau \right]\text{，}$ (12)

 $\tau = \frac{{\left| {N( \pm )} \right|S}}{{I\delta }} \times {10^2}{{ MPa}}{\text{。}}$ (13)

3 结　语

1）满载状态时FPSO船体处于中垂状态，最大静水剪力和弯矩分别位于距船尾0.75 L和0.55 L附近；而压载时船体处于中拱状态，最大静水剪力和弯矩分别位于距船尾0.9 L和0.25 L附近。

2）FPSO在满载和压载状态时的波浪剪力和弯矩的长短期预报值均是关于船中呈对称分布，只是最大值的位置不同。波浪剪力预报值在船中附近最小，而在距船首尾1/4 L附近最大；波浪弯矩的预报值均是在船首尾位置为0，而在船中附近最大。此外，满载时的波浪载荷预报值基本要比压载时大，而且长期预报值均大于短期预报值。

3）FPSO目前状态的总纵弯曲与剪切强度均满足《钢规》的要求，但船体在目前状态不进行任何维护的前提下，继续服役至40年时，船体总纵弯曲强度将严重不满足《钢规》的要求，而总纵剪切强度仍满足《钢规》的要求。对于本文中的FPSO，其总纵剪切强度不是主要的强度问题，应主要关注其总纵弯曲强度，在延期服役过程中应定期进坞进行除锈涂漆维护和换板加强。

 [1] 周守为, 曾恒一, 范模. 我国浮式生产储油装置的研制与开发[J]. 中国海上油气, 2006, 18(2): 73–78. ZHOU Shou-wei, ZENG Heng-yi, FAN Mo. Floating production, storage and offloading system researched and developed in China [J]. China Offshore Oil and Gas, 2006, 18(2): 73–78. http://d.wanfangdata.com.cn/Periodical_zghsyq-gc200602001.aspx [2] 《海洋石油工程设计指南编委会》. 海洋石油工程FPSO与单点系泊系统设计[S]. 北京: 石油工业出版社, 2007. Editorial Board of Guidelines for Offshore Oil Engineering Designing. Design of offshore oil engineering FPSO and single point mooring system [S]. Beijing: Petroleum Industry Press, 2007. [3] 唐文勇, 张道坤, 刘坤, 等. 考虑腐蚀影响的FPSO风险接受准则研究[J]. 船舶力学, 2013, 17(5): 502–512. TANG Wen-yong, ZHANG Dao-kun, LIU Kun, et al. Study on risk acceptance criterion of FPSO considering influence of corrosion [J]. Journal of Ship Mechanics, 2013, 17(5): 502–512. http://www.cnki.com.cn/Article/CJFDTOTAL-CBLX201305008.htm [4] JOEM K P. Ship hull ultimate strength reliability considering corrosion [J]. Journal of Ship Research, 1998, 42(2): 154–165. [5] 马巍巍, 范模, 李达, 等. 提高老旧船形浮体总纵强度探讨[J]. 中国海上油气, 2011, 3(1): 66–70. MA Wei-wei, FAN Mo, LI Da, et al. Research on raising longitudinal strength of old ship shape naval architecture [J]. China Offshore Oil and Gas, 2011, 3(1): 66–70. [6] 邱世欣, 赵胜涛, 胡楠, 等. FPSO 延期服役评估方法[J].中国修船, 2013, 26(1): 52–54. QIU Shi-xin, ZHAO Sheng-tao, HU Nan, et al. Extended service evaluation method for FPSO [J]. China Shiprepair, 2013, 26(1): 52–54. [7] 中国船级社. 油船结构直接计算分析指南[S]. 北京: 人民交通出版社, 2003. China Classification Society. Guide for directing calculation of oil tanker structure [S]. Beijing: China Communications Press, 2003. [8] 戴仰山, 沈进威, 宋竞正. 船舶波浪载荷[M]. 北京: 国防工业出版社, 2007. [9] 刘水庚译. BEREARD MOLIN著. 海洋工程水动力学[M]. 北京: 国防工业出版社, 2012. [10] 中国船级社. 海上浮式装置入级与建造规范[S]. 北京: 人民交通出版社, 2013. [11] 中国船级社. 钢质海船入级与建造规范[S]. 北京: 人民交通出版社, 2006.