Valve Magazine - Summer 2011

or how it is determined might be described in the following simplified sequence:

Fitting Types

; A decision is made that a process plant needs to comply with the international standards for process safety systems, usually IEC 61511.

; The plant forms a HAZOP (Haz-
ard and Operability Study) team.
Essentially the HAZOP procedure
involves taking a full description
of a process and systematically
questioning every part of it to
establish how deviations from the
design intent could arise. Once
identified, an assessment is made
whether such deviations and their
consequences can have a negative
impact upon the safe and efficient
operation of the plant. If consid-
ered necessary, action is then
taken to remedy the situation. In a
sense, this is based upon Murphy’s
from the system. Just like the seating
surfaces on valves, the seats of a union
must be kept clean and free of scratches.
Table 2 lists the piping component
classes for a hypothetical application.
aded or socket weld pipe to a larger diameter
e of a tee
s together at 90-degree angles in the
similar pipe sizes
r branching at a 45-degree angle from
internally threaded fitting for connecting
eaded end pipe
esigned to thread inside female pipe threads
a pipe
esigned to thread onto the outside of
ponents and seal the pipe
g component that allows pipe or piping
asily removed for alteration or maintenance
law: Anything that can go wrong,
WILL go wrong. What the
HAZOP team attempts to deter-
mine is: What will go wrong? The
team might be comprised of
process design engineers, opera-
tions personnel, maintenance and
instrumentation engineers, etc.

PFDAVG See Detail Time 1 0.1 0.01 0.001 0

Figure 2. PFDAVG and Valve Life Cycle

Graphs reprinted by permission from ANSI/ISA- TR96.05.01-2008. ©ISA 2008

End of Life

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of
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GRADES:
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A105

A350 LF2 SA105

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F- 11

include escalating examples, but the possibilities are endless. In other words, the list might address: “If the system fails…:”

• The plant will lose $15,000 per day.

• The plant will lose $1 million per day.

• The plant will become damaged and will shut down for three weeks.

• A high degree of probability exists for injury or loss of life to company personnel in the immediate area.

• A high degree of probability exists for explosion and loss of life to non-company personnel outside the parameter of the facility.

lly
Ultimately, it is up to the plant owner
and operator to determine what level of
risk is acceptable based on their own
criteria (best practice, company philoso-
phy, insurance rates and requirements,
budgets, etc). Therefore, risk tolerance
is subjective and site-specific.