Hydrocarbon leak

However, in the case of a root cause analysis system, a much more comprehensive evaluation of the structure of the accident is required. This is necessary to unravel the often complex chain of events and contributing causes that led to the accident occurring. A number of techniques are available to describe complex accidents. Some of these, such as STEP (Sequential Timed Event Plotting) involve the use of charting methods to track the ways in which process and human events combine to give rise to accidents. CCPS (1992d) describes many of these techniques. A case study involving a hydrocarbon leak is used to illustrate the STEP technique in Chapter 7 of this book. The STEP method and related techniques will be described in Section 6.8.3. 

The first case study describes the application of the sequentially timed event plotting (STEP) technique to the incident investigation of a hydrocarbon leak accident. Following the analysis of the event sequence using STEP, the critical event causes are then analyzed using the root cause tree. 

CASE STUDY 1 INCIDENT ANALYSIS OF HYDROCARBON LEAK FROM PIPE... 

FIGURE 7.1. Simplified Process Diagram Hydrocarbon Leak From Pipe (from Cullen, 1990). 

FIGURE 7 2 STEP Diagram of Hydrocarbon Leak from Pipe, Page 1 of 4. 

The hydrocarbon leak probably resulted from a blank being incorrectly fitted to pump A PRV pipework and subsequent failure to provide a leak-tight seal. 

Oil and hydrocarbon leaks. FW system fouling and deposit binding Non-wettable boiler surfaces. 

Oil and hydrocarbon leaks that return with the condensate coat heat-exchange surfaces and cause FW system fouling and deposit binding. These materials must be removed or they will reenter the boiler to produce nonwettable boiler surfaces, and create serious problems. Oil in condensate should be removed by the use of an inline pre-coat filter. The pre-coating should be either aluminum hydroxide ox ferric hydroxide becaue both these hydrous oxide gels have an affinity for oil. 

Possible hydrocarbon leaks points at process cooling towers. 

Feed contaminated with heavy hydrocarbons] leak in heat exchangers/partly open valves. [Feed contaminated with light hydrocarbons leak in heat exchangers/partly open valves. 

Hydrocarbon leak, fire - Escape routes from areas... 

Figure 1 shows the trend for hydrocarbon leaks over 0.1 kg/s, normalised against installation years, for all types of production installation, from the annual report for 2007, see PSA (2008). The figure illustrates the technique used throughout the Risk Level Project in order to evaluate the statistical significance of trends. 

The main emphasis is on barriers against hydrocarbon leaks in the process area, comprising the following barrier functions ... 

We have postulated that on an installation level, lagging (incident based) indicators are not suitable, see Vinnem (2009). This is because the incidents will be too rare, say typically once per year. The only exception is the number of critical hydrocarbon leaks (say above 0.1 kg/s). This will formost installations be less than once per year, but should still be focused upon, due to the high awareness associated with such hydrocarbon leaks, because of their potential to cause major catastrophes. 

The average incidence rate for such hydrocarbon leaks has been around 0.3 leaks per installation per year on the Norwegian Continental Shelf But there are large variations, up to 2-3 critical leaks per year on some installations. 

Vinnem, J.E., Seljelid, J., Haugen, S. Husebo, T. 2007b. Analysis of Hydrocarbon Leaks on Offshore Installations, presented at liSREL 2007, Stavanger, 24-27 June, 2007... 

The refinery had experienced a long history of frequent flange leaks and occasional fires during exchanger startups. Typically, as the exchanger system temperature rose from ambient temperature to 500°F there were hydrocarbon leaks at gaskets until the temperatures lined out. 

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