**3.3 Monitoring and seismic protection of offshore platforms**

One essentially important question in the problem of protection of objects of offshore and land infrastructures is provision of SP seismic stability; this can be achieved with the help of developed scientific bases of design of self-lubricating, and self-adjusting sliding supports with reverse motion used as seismic-insulators for bridges, industrial and civil constructions. These works are also used for oil and gas offshore platforms on the continental shelf of the Russian Federation on the Sakhalin Island [1, 2, 17, 18].

It was proposed offshore structures protection against earthquakes to use the friction pendulum bearings (FPB) as the seismic-insulators [1, 12–14]. A calculation method for the service life of a FPB and the method of assessment of friction coefficient were experimentally developed [17, 18].

The real possibility of pendulum sliding supports use as efficient mean for absorption of energy from external force appeared in the last 30–40 years thanks to development of new technologies (in particular in connection with development of space research works in the USSR and the USA) and to introduction of new tribotechnical materials (such as the antifriction self-lubricant weaved fibrous materials).

In the SP pendulum bearings used are pendulum characteristics, providing increase of the natural oscillations (vibrations) period of the isolated structure in a manner to avoid the maximal forces occurring at an earthquake. During an earthquake, the articulation slide block in the bearing moves (slides) along a stainless steel concave surface, forcing a support to move within small pendulum displacements. The schematic view of the bearing is presented in **Figure 20**. The plate with a spherical concave surface is mounted on the top as viewed from the deck; this is done to arrange convenient operation. At such location of a concave plate, the grease does not get on the slide face. The lower plate of the case is mounted on the jack structure.

If forces occurring during an earthquake do not exceed the level of friction forces, then the structure supported by the bearing corresponds to the standard structure lying on the jack and has its own oscillation (vibration) period without insulator. As soon as the level of friction forces is exceeded, the structure starts oscillate with designed period; at that the dynamic response and damping are defined by bearing properties.

The hemispherical design of the articulation slide block allows getting relatively uniform distribution of pressure under the slide block and this reduces the movement judder and prevents occurrence of high local pressure in the bearing.

**Figure 20.** *Bearing structure diagram.*

• flow chart and fault-tree construction techniques (**Figure 11**);

• risk-based inspection (RBI) technique developed by Shell Global Solutions International company for residual life evaluation and planning of the objects' high-pressure equipment health monitoring frequency with consideration of risks-analysis (**Figure 18**). Inspections and tests planning is performed upon analysis of data about current technical condition of specified equipment item.

In the approach (**Figure 19**) presented above by analogy with **Figure 4**, the classes and categories of criticality, consequences of damages from accidents and

The risks analysis technique is based on information about scenarios of dangerous situations and probabilities of their occurrence received a priory. It is possible for SP for which design and operation experiences are accumulated already. In engineering design performed according to clauses 2.9–2.12, the inspections fre-

quency can be obtained upon calculations as per expressions (18)–(41).

• probabilistic modeling technique (**Figures 7** and **8**); and

*Basic diagram of implementation risk based inspections technique.*

*Probability, Combinatorics and Control*

**Figure 18.**

**Figure 19.**

**108**

*Criticality and risks matrix.*

accidents can be assessed in a similar way to **Figure 4**.


works with regard to technogenic safety [1, 2, 4, 5, 7, 15, 16]. So far, the solution of these tasks is difficult because of absence of enough nomenclature and number of means for multi-parameter and multi-factor diagnostics of the damaged SP elements with taking into account scenarios of accidents. When looking for methods and diagnostic means and monitoring performance, it is necessary to apply the system concept providing umbrella approach for: the preliminary analysis of the stress-deformed states by analytical and numerical methods; identification of the most loaded and dangerous zones; nondestructive testing and diagnostics at all stages of equipment life cycle; and development of a system of diagnostic data collection and exchange between design offices, manufacturers and operators.

*Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States…*

Only based on this understanding, it is possible to provide high system reliabil-

Along with expert evaluation of above-water and above-ice technologies, the feasibility studies and assessment of basic features of subsea systems, including issues of energy security, were carried out. This analysis is made by the community of the specialized sea organizations: RNTs "Kurchatov institute" and Institute of machine science named after A.A. Blagonravov RAS (Moscow) with participation

As a solution acceptable from the economical and technical point of view of above task is related to the transition to the system of underwater and under-ice technology of exploration, production, treatment and transportation of hydrocarbons (oil and liquefied natural gas—LNG (**Figure 22**) that so far is not available. Higher price of such underwater and under-ice system is compensated by the reduction of the subsequent costs required to provide safety and physical protection. Estimates show that the possible losses caused by technogenic accidents of above-water natural threats and terrorist impacts on the objects of a underwater technologies complex is 10 times less, than from impact of similar risk factors for traditional above-water technologies. The appraisals done by the specialized organizations show the technical capability of Russia to develop for the Arctic shelf the

Calculations done with taking into account information from clause 2 make it possible to obtain the risks values for both traditional (on-land and above-water sea) technologies and for new (underwater) technologies. The following risks'

*Use of frictional pendulum bearings (sliding supports) on sea oil platforms installed in the top part of four*

**3.5 New offshore subsea technology solution for shelf development**

ity, sufficient depth and validity of diagnosing.

*DOI: http://dx.doi.org/10.5772/intechopen.88894*

of the National laboratory Sandia (USA).

**Figure 21.**

**111**

*concrete jacks. a) PA-B Platform; b) Lun-A Platform.*

underwater and under-ice atomic technologies (**Figure 22**).

#### **Table 4.**

*Average side accelerations д(m/sec<sup>2</sup> ) of the oil and gas platform components when pendulum bearings are used (a) and without such bearings (b).*

As the displacements caused by an earthquake initially occur in bearings that are seismic-insulators, the side loadings and vibration motions transferred to a construction drop significantly.

In **Table 4**, the mean peak accelerations are presented, influencing, at designed earthquake, on the components of the oil and gas platform Lun-A for cases when friction pendulum bearings are in use and are not in use.

Accelerations drop is at 1.5–3 times that leads to significant reduction of wear of bearings and the antifriction self-lubricant film.

Development of oil and gas fields, as a rule, is carried out in the seismically active areas (their activity reaches magnitude 8–9 on 1–9 scale), and this is one of the main difficulties to be overcome in the process of such developments execution.

Sea platforms "Lun–А" and "PA-B" of the Sakhalin-II project are installed on the shelf of the Sakhalin Island in 2007. The weight of the gravity based structure is: for the"Lun–А" platform—103 thousand tons and for the "PA-B" platform—106 thousand tons. The weight of the topsides of "Lun–А" is 28 thousand tons and of "PA-B"—34 thousand tons. Service life of sea platforms "Lun–А" and "PA-B" is 30 years. Their design shall provide operation of equipment without damages and failures and resist loads occurred in the process of earthquake with probable repeatability once in 200 years and keep running without serious damages after impact upon such seldom earthquake that may occur once in 3000 years.

For the first time in world practice on "Sakhalin-II" project were installed frictional pendulum sliding supports (**Figure 21**) to provide seismic insulation between sea platform concrete gravity based structure and topside.

Such FPB previously were used for construction of highways, bridges and airports never before they were used in sea platforms.

Four bearings—seismic insulators installed in the catwalk of four concrete supports provide damping of extreme horizontal loadings due to isolation of the topside buildings from the most destructive pushes and due to reduction of loads on the topside buildings caused by impact of daily temperature changes, pressure of ice and waves.
