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IPF Study

  • IPF (Instrumented Protection Functions) are functions which comprises of

· One or more initiators

· A logic solver or an Instrumented Protection System. Some refer it to as PLC

· One or more final elements

With the purpose to prevent and mitigate hazardous situations

  • IPF Study is a study which consists of

1. SIL Classification (Proceed with all)

2. IPF Verification

3. IPF Implementation

4. IPF Review – Every 5 years

  • SIL Classification

· Most time consuming

· Classifying consequence of IPF failure upon demand (Dangerous Failure)

· Classifying consequence of IPF initiated without demand (Safe Failure/ Spurious Trip/ Nuisance Trip)

· Classifying demand rate. Demand rate is a scenario that causes demand for an IPF

· To assign SIL

· No calculation – just assign SIL. In verification will only be calculation

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· SIL Requirements

o 0 no IPF required – In PPTSB 90% was SIL 0

o a1 – Pre-alarm is adequate

o a2 – Triggers a switch action (interlock from DCS) + pre-alarm. Can integrate with control function

o 1 – Triggers switch action + pre-alarm.

§ Final Element can be control valve if fail safe

o 2 – Trigger switch action + pre alarm

§ Final element can be control valve in 1oo2

§ Share initiator with control transmitter in 1oo2

o 3 – Trigger switch action + pre-alarm

§ Share initiator with control transmitter in 2oo3

o 4 – Shall be avoided, very low PFD, more economical to redesign

· PFD

o Sil 1 : 1/10

o Sil 2 : 1/100

o Sil 3: 1/1000

o Sil 4 : 1/10000

  • SIL Verification

· To verify the installation at site. Look for common installations. Audit like

· Calculate the PFD (Probability of Failure Upon Demand)

· To obtain as low as SIL requirement

· Is calculated by obtaining

· HWFT (Hardware fault tolerance)

· DCF(Diagnostic Coverage Factor)

· Safe Failure Fraction (SFF)

· Number of safe failures vs number of total failures

· Proof Test Coverage Factor

· How much unsafe failures one covers during testing

· Test and repair durations

· Mission Time

· The time between test intervals

· Mission – The mission is referred to the mission the IPF is taking during it’s operation

· The smaller the mission time, the lower the PFD

·

·

· 2 Layers of verification

· Architectural Constraint. Consists of the following :-

· Hardware Fault Tolerance (HWFT)

· Is the tolerable number of dangerous failures in the IPF

· For 2oo3, HWFT = 3-2 = 1.

· For 1oo3, HWFT = 3-1 = 2

· For 2oo2, HWFT = 2-2 = 0

· Safe Failure Fraction (SFF)

· Any hardware can be

· Working Normally

· Safe Failure

· Dangerous Failure (Already failed but not known)

· SFF is the ratio of safe failures to the total number of possible failures (Safe + Dangerous)

· Provided by manufacturer

· Type of Instruments

· Type A – All failure modes and effect known. Well documented.

· Type B – Complicated Instruments

SFF

HWFT

0

1

2

< 60%

SIL 1

SIL 2

SIL 3

60% - 90%

SIL 2

SIL 3

SIL 4

90% - 99%

SIL 3

SIL 4

SIL 4

> 99%

SIL 3

SIL 4

SIL 4

Type A Instrument Used

SFF

HWFT

0

1

2

< 60%

N/A

SIL 1

SIL 2

60% - 90%

SIL 1

SIL 2

SIL 3

90% - 99%

SIL 2

SIL 3

SIL 4

> 99%

SIL 3

SIL 4

SIL 4

Type B Instrument Used

Safety Integrity Levels (SIL)

· Safety Integrity Levels (SILs) are a safety-measurement standard defined by IEC in IEC61508 to quantify the chance of dangerous failures in electrical or electronic safety devices, that is, the probability of the device to fail in performing its Safety function.

· Four SIL levels are possible, with SIL4 being the most dependable and SIL1 being the least. Each are based on it’s corresponding PFD (Probability of Failure Upon Demand) – Which is the probability that an instrument will not respond to a demand. It usually works on frequency of demand

SIL

PFD

· 4

· 10-5 to 10-4

· 3

· 10-4 to 10-3

· 2

· 10-3 to 10-2

· 1

· 10-2 to 10-1

· TÜVs (Technischer Überwachungsverein) are German organizations that aim to protect humans and the environment against hazards coming from factories and mechanisms of all kinds. As an independent consultant, it examines monitoring-needy plants, motor vehicles, energy installations and devices. The many subsidiaries of the TÜVs can also appear as project developers for energy and traffic concepts, problem solutions in the area of environmental protection and certification bodies

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OPEN-PLANT PTY LTD

Perth, Australia

EMAIL

info@open-plant.com
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