Dmitrii M. Lazarev
NOVATEK Public Joint Stock Company, Moscow
Abstract: The article discusses the aspects of hazards and risks arising in the process of production and transportation of liquefied natural gas (LNG). The concept of quantitative risk assessment as a mechanism for reducing the dangerous effects of LNG is considered, a scheme for quantifying risks and ways to reduce them in the event of hazards during LNG operation is proposed.
Keywords: liquefied natural gas (LNG), hazards, risk, quantitative risk assessment, risk criteria, risk reduction, HAZID method, HAZOP method
Introduction Equipment for the production, processing and transportation of LNG must operate in the normal mode and provide the necessary economic and production effect, carrying out the production and processing of liquefied natural gas, providing jobs to employees of the oil and gas industry and bringing profit to the producing organization.
This is especially important for the high quality and timely implementation of sufficiently large volumes of LNG ship deliveries in the Far East and the Asia-Pacific region, where the LNG plant of the “Sakhalin-2” project, located in the south of Sakhalin Island, operates.
However, in the process of work, emergencies or malfunctions often occur, often accompanied by the occurrence of the following types of harm:
1. Illness, injury or, in serious cases, death of workers.
2. Termination of gas production or impossibility of further work.
3. Damage to property and investments.
4. Damage to the biological environment.
Situations causing such harm are called hazards. Any fuel tank is a potential source of danger as it may cause LNG leaks and / or fire. The term “danger” itself does not assess the probability of the event itself and of the harm that actually can be caused, and the definition “serious danger” describes an object that can cause significant damage or lead to great casualties.
One of the practical characteristics of “danger” is its actual occurrence – an unexpected unintentional deviation from the standard conditions leading to any kind of harm. Examples range from minor incidents such as a small gas leak to major accidents such as equipment fires.
In turn, risk is a combination of the likelihood and consequences of such incidents. In relation to science, risk is characterized as the probability of a certain negative event occurring in a certain period or under specific circumstances. Probability is expressed as the frequency of events per unit of time, or as the probability that an event will occur under specific circumstances. When assessing the consequences, the degree of harm caused as a result of the event is taken into account.
The distinction between “danger” and “risk” is very important, but in everyday speech, as well as in popular dictionaries, risk and danger are described as almost similar terms in meaning.
“Risk” is rarely used as a term equivalent to “danger” (for example, a high-risk object, a low-risk action, etc.), but often as a precise scientific term with a number of explanations (for example, the risk of disruption of the escape route due to a gas fire, or the individual annual risk of death for industrial facility worker).
“Security” (“safety”) are the opposite of “risk”: the greater the risk associated with professional activities or facility operation, the less secure / safe they are. The widely used interpretation of safety seems to be “zero risk”, but in fact, this is not possible in the oil and gas industry, which is characterized by increased danger of the work performed.
In this regard, a quantitative risk assessment of oil and gas industry facilities has been widely used to reduce the harmful effects of dangerous goods in the world practice.
The concept of quantitative risk assessment
The most common risk management tool is a quantitative risk assessment, which is based on the identification of numerical values for any risk, due to which it is possible to assess the degree of impact and the likelihood of risks [4].
The purpose of quantitative risk assessment:
1. Identification and quantification of key technological hazards associated with the field of activity.
2. Analysis of the compliance of risks for people according to internationally approved criteria.
3. Study of the main risk factors, for the subsequent development of potential risk mitigation measures.
The scheme for conducting a quantitative risk assessment is clearly shown in Figure 1.
Data collection consists in studying process flow diagrams, identifying critical points, compiling a heat and material balance, a detailed description of a specific stage of the process, studying the general plan of sections, developing or analyzing an algorithm for an emergency shutdown and blowdown system, calculating the base load on equipment during the production and transportation of LNG etc.
The collection and analysis of initial data is already a more in-depth study of the hazard, for example, calculating the frequency and determining the location of leaks for equipment, valves, etc.
Hazard identification can be carried out using the HAZID method. The HAZID method, or hazard identification, serves as a qualitative method for analyzing the hazards of technological processes, the purpose of which is to identify the main hazards, hazards and events that can disrupt or harm specific activities or the entire technological system of a hazardous production facility in general [5].
The HAZID analysis itself is a structured risk identification and analysis method that allows you to document the hazards according to the project at the slightest sign of the occurrence of hazards and, accordingly, risks. The HAZID method is recommended to be used at the initial stages of creating project documentation in conditions of lacking or incomplete information [1].
It is also recommended to use the HAZOP method for a more detailed clarification of the causes of possible risks [3]. The meaning of the method is to build perturbation models. One element of the system is a source of disturbance, and the second is a receiver. The first shows the causes of the deviation, and the second shows the consequences that this disturbance or deviation contributes to, and how it affects the technological process and the final result (Figure 2).
Frequency analysis Failure rates are determined for any event in order to investigate a probabilistic risk assessment. In most cases, a number of methods are used to determine such frequencies. The approach bases on the systematization of data obtained from different stages of the process. As a result, failure rates are calculated for equipment items, data on which were obtained from failure reports from a number of objects. For this purpose, DNV has developed an extensive generic failure rate database that is compiled in its own DNV LEAK 3.2 software (Fig.3).
These leak rates are based on data from UK “Health & Safety Executive for offshore facilities” to map the base load LNG plant project which is land based and has ‘clean’ maintenance. LEAK software implements new leak rates for pipes and technological tanks. This program is used to establish the cumulative frequency of leaks, further used in the risk assessment.
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