Hi
I need MTTF data for a Non-SIS DeltaV to calculate PFD (probability of failure on demand), any help appreciated.
Best regards
Andi
Hi Andi.
I had this document at one time for the same purpose in 2009. I searched around for it, but can't find it. I had to ask my LBP for the document I believe, though. I looked for it on the internet hoping maybe it had been published by now, but I didn't have much luck quickly.
I did find an independent study of M Series Controllers done by AIChE. Link is here:
www.emersonprocessxperts.com/.../IntegrationOfComplexSequencesUsingDeltaV.pdf
Brian McWhorter ISA:CAP OPC:SI PE:CSE
Emerson does not provide individual component MTTF. MTBF and availability are calculated on a system basis for a given BOM.
Having said that - component MTTF is not sufficient for determining PFD. Perhaps if we understood what you are trying to do we could help. Please note DeltaV is NOT certified as a safety system and information for determining PFD , SFF etc is not available.
I would recomend you contact your local Emerson representative so they can help you with what you are trying to achiieve.
In reply to Gary Law:
Andi,
As Gary Law has commented, Regular DeltaV (basic process control) is not certified as a safety system. So, I am not quite sure as to what purpose the PFD numbers (for regular DeltaV system components) might achieve.
Over the last 10-12 years I have collected some failure data (only module failures and how long they have been in service until the time of failure) for some reliability studies within our organization. The data collection covers several DeltaV systems (small, medium and large systems with various types of modules and controllers) and over 5-12 years of being in service. But, I would not try to put PFD or MTBF labels on this data. The data helps to establish some prior use information for our company internal use. I am sure there are other users who may have done similar studies.
Kris Chandrashekar
In reply to Kris Chandrashekar:
Dear All,
Thank you, I wanted to calculate a high level interlock and low level interlock loop PFD
# Case 1. High level interlock to prevent overfill of a Tank
The interlock logic was made inside DeltaV. The level sensor/transmitter monitoring the tank level is also connected to DeltaV AI, the DeltaV then connect through a serial card to a Siemens S7, The siemens S7 connect to a VSD ABB ACS550 which driven a pump responsible to fill the tank. When High interlock logic satisfied, then DeltaV will send command to Siemens S7 to stop filling (during transfer) or to inhibit filling/transfer.
# Case 2. Low level interlock to maintain minimum safe level inside a tank for its agitator to operate and inhibit transfer from the tank.
Logic inside DeltaV, Level sensor connect to deltaV, DeltaV output to an AS-i card to a P&F AS-i module and then to a Relay than to VSD ATV32.
For deltaV sis there is certificate of failure rate as below
www2.emersonprocess.com/.../CERT_Exida_DeltaV61508.pdf
and
www.exida.com/.../Emerson_09-10-23_R001_V1_R1_IEC_61508_Assessment.pdf
But for non sis, I could not find any document, so I want to calculate from MTTF or MTBF if this data is available.
Am I doing it correctly? please advise
In reply to Andi nurcahyo:
As previously stated DeltaV is not certified as a safety system and thus the information for PFD calculations is not available.
Looking at what you are doing I would not attempt to assign any PFD to these interlocks.
In Case 1 - even if DeltaV were certified, then the Serial comms would also need to be certified (which it isn't) AND the S7 PLC AND ABB VSD would need to be taken into consideration. (Or you would need the PFD for these other components)
In Case 2 - the ASi card AND P&F ASi module would need to be certified (or PFD needed).
In ALL cases PFD cannot be determined from MTTF alone.
If you are wanting to take credit for the risk reduction (LOPA) due to these interlocks in the BPCS I would recomend you simply take a minimum credit as allowed by your plant procedures and not attempt to perform an analysis / justification based on attempting to calculate PFD.