4 replies to this topic

[Purnesh Meshram]

Dear All,

 

I am preparing a safegaurd memorandum for Sulfur handling facility.

I would like to know.

1) What basically this documents contained. i check some of the previous documents which even makes me confused.

2) What is the meaning of Instrumented Protective Functions. considering ultimate safety, is emergency shutdown logic is IPF, or all the logics or if not what its this functions basic need.

3) What is Penultimate Safeguards.

 

Please share your thoughts.

thanks

 

[dnrakesh2006]

hi,

 

1. safeguard memorandum describes the relief devices and safeguards by instrumentation that are provided to protect against uncontrolled loss of containment.

 

2. ultimate safe guards : Systems or elements that serve as the ultimate level of protection against uncontrolled loss of containment, e.g. relief valves rupture disks and instrumented protective functions

 

3.Penultimate safeguards are instrumented protective functions that act as the penultimate level of protection against an uncontrolled loss of containment. They can include pressure, temperature and level safeguards

 

if you are preparing this document there should be a company guideline  to prepare the same and follow it.

 

it takes lot of effect to prepare this document you need all P&ID, equipment data sheets, IPDS, ESD valve list , flare and relief system report, and more importantly  you should know how the entire plant is protected.

 

hope this helps,

Edited by dnrakesh2006, 08 November 2013 - 03:35 AM.

[Purnesh Meshram]

thanks Rakesh 

 

I understood what you explain. However, my system is tanks and pumps there is no flare line. let me explain to you what exactly i am looking for.

1) Tanks has some logics with safety interlocks categories as emergency and other interlocks..for example:  HHL trips for inlet valves, and divert re circulation to other tanks to avoid overfilling in the tank. is this IPF.

2) Tank has 2oo3 voting for avoiding high temperature in case of fire initiated inside the tank, might H2S PP goes in LEL or HEL. this will start snuffing steam to protect. is this IPF.

3) all the tanks have vents instead of PVRV for breathing and out breathing is this vent comes under ultimate guards.

4) Should all the ROVs to be considered under mitigation.

 

thanks in advance...

 

Company philosophy is as below for ref.

SAFEGUARDING PRINCIPLES

A process safeguarding system is required to protect against uncontrolled loss of containment. Uncontrolled loss of containment occurs when the process variables (usually the pressure and the temperature) exceed the design limit to such an extent that the process equipment fails to contain the process materials.

Process safeguards are classified as ultimate, penultimate and mitigating systems. These are described below.

2.1 ULTIMATE SAFEGUARDS

These serve as the ultimate level of protection against uncontrolled loss of containment. These include the following:

• Pressure relief valves

• Rupture disks

• Thermal expansion valves

• Safety instrumented systems (SIS) against loss of containment.

Note: SIS can only be used as an ultimate safeguard after multi-disciplinary review and with IPMT approval.

2.2 PENULTIMATE SAFEGUARDS

These are generally instrumented trips that serve as the penultimate level of protection, against uncontrolled loss of containment. Penultimate safeguards are typically associated with process shutdowns that are designed to constrain the process variable (flow, pressure, temperature or level) within safe operating ranges. The process is thus prevented from reaching an emergency state where ultimate safeguards are required in order to prevent uncontrolled loss of containment.

Typical examples are:

• Burner management systems on fired heaters (to be developed in EPC phase)

• High High level trips on compressor suction drums

• High High temperature trips on reboiler shutting off heating medium

• Low Low level trips on vessels upstream of pumps

• Low Low level trips on high pressure separators

• High High pressure trips downstream of pressure reducing stations

• Low Low flow trips on furnace feed lines

• Low Low flow of H2 to reactor systems

2.3 MITIGATING SYSTEMS

These limit the consequences of an uncontrolled loss of containment. Mitigating systems do not offer protection against loss of containment, but are used to bring the plant into a safe condition in an emergency thereby limiting the consequences of an uncontrolled loss of containment.

These typically include:

• Emergency Shutdown valves, i.e. ESDV.

• Emergency Depressuring systems e.g. EDP valves.

• Remote Operated Valves, i.e. ROVs, in suction lines of pumps and even manual block valves

• Pressure control valves e.g. vent to flare

• Capacity determining components e.g. elements such as control valve sets or restriction orifices that govern the sizing of the downstream relief system.

Edited by chemtechiee, 12 November 2013 - 03:05 AM.

[Sharma Varun]

 

thanks Rakesh 

 

I understood what you explain. However, my system is tanks and pumps there is no flare line. let me explain to you what exactly i am looking for.

1) Tanks has some logics with safety interlocks categories as emergency and other interlocks..for example:  HHL trips for inlet valves, and divert re circulation to other tanks to avoid overfilling in the tank. is this IPF.

Yes it is is an Instrument protective function.

2) Tank has 2oo3 voting for avoiding high temperature in case of fire initiated inside the tank, might H2S PP goes in LEL or HEL. this will start snuffing steam to protect. is this IPF.

This is amitigating system.

3) all the tanks have vents instead of PVRV for breathing and out breathing is this vent comes under ultimate guards.

These can be considered as ultimate sfeguards provided you check their adequacy.

4) Should all the ROVs to be considered under mitigation.

 On a broader scale yes but you may have exceptions.

 As such safeguarding memorendum is a SHELL design engg. practice & SHELL DEP is best guideline to understand the same. Based on guidelines provided by you and my experiecnce I have tried to answer your queris hope it helps.

[Purnesh Meshram]

thanks Rakesh and Varun