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Risk Analysis applied to Subsea Pipeline Engineering 283

CWPL= cost of implementing the risk reducing measure.
COP= net present value of operational cost related to the measure.
CRED= net present value of expected benefits as a result of the risk reducing measure.

16.3 Identification of Initiating Events

Identification of initial events is regularly referred to as hazard identification, in the offshore
industry. The main techniques that exist are:

Check Lists- Review of possible accidents using lists which are developed by experts
Accident and Failure Statistics- Similar to the checklists but are derived from failure
events.
Hazard and Operability Study- Used to detect sequences of failures and conditions that
may exist in order to cause an initiating event.
Comparison with detailed studies- Use of studies, which broadly match the situation being
studied.

After the completion of this investigation it is necessary to examine the hazards and identify
the significant hazards which need to be analyzed further.

16.4 Cause Analysis

16.4.1 General
There are two purposes of cause analysis; firstly, it is necessary for the identification of the
combinations of events that may lead to initiating events. Secondly, it is the assessment of the
probability of the initiating event occurring. The initial one is a qualitative assessment of the
system and the latter is quantitative.

In pipeline engineering the scope of examining causes can vary depending on the
requirements of the risk analysis. Often it is only necessary to analyze the material failure
mechanism by which the initiating event occurs (fatigue, corrosion etc). This is achieved by
implementing a reliability analysis (quantitative). Less often it is necessary to map a sequence
of events that lead to the initiating event (qualitative and quantitative). This may include
aspects such as trawling impact or humadsystem error.

The qualitative analyses aim to; detect all causes and conditions that could result in an
initiating event and develop the foundation for possible quantitative analysis. The aim of the
quantitative analyses is to determine a probability value for the occurrence of an initiating
event. The analysis tools that are available are stated below. This chapter will discuss only the
first two approaches.