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Copyright 2004, Society of Petroleum Engineers Inc.

This paper was prepared for presentation at The Seventh SPE International Conference onHealth, Safety, and Environment in Oil and Gas Exploration and Production held in Calgary,

Alberta, Canada, 2931 March 2004.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in a proposal submitted by the author(s). Contents of the paper, as

presented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect any

position of the Society of Petroleum Engineers, its officers, or members. Papers presented at

SPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paperfor commercial purposes without the written consent of the Society of Petroleum Engineers isprohibited. Permission to reproduce in print is restricted to a proposal of not more than 300words; illustrations may not be copied. The proposal must contain conspicuousacknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O.

Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abst ractProtection of pressurized process equipment against fire and

thus reducing the risk of fire escalation is a key concern for allprocess plants both offshore and onshore.

Guideline for Protection of Pressurized Systems Exposed toFire, referred to as the guideline, was developed by Norsk

Hydro, Statoil and Scandpower Risk Management in 2002.The guideline has been applied in offshore developmentprojects. Based in the experiences gained from users, theguideline is being revised December 2003. The procedures setforward in the guideline, has pointed out several areas/topicswhere further research and testing should be implemented.One such topic is behavior of flanged connection duringrealistic hydrocarbon fire scenarios. Therefore, large scale

experiments on jet fire exposed flange connections underpressurized conditions are carried out during the winter2003/2004.

The guideline is under continuous development and will be

updated when new knowledge is gained and available.

IntroductionThe development of this guideline was initiated by the needfor a comprehensive approach including all the main aspectsrelated to optimizing fire protection of pressurized processequipment and systems. The results from the recent years fire

research on hydrocarbon fires in offshore like environments,also indicated that such fires can expose equipment moreseverely than recognized in other guidelines that arecommonly used.

The guideline defines the principles and a methodologythat should be adopted for design, construction and operation

of systems and arrangements for fire protection of pressurizedprocess piping and equipment.

The guideline is valid for on- and offshore processfacilities.

The guideline has been developed in line with theprinciples outlined in ISO 13702, Ref. /1/, and hence, alsorepresents an important contribution to the establishment of a

Fire and Explosion Strategy, FES.The guideline is applicable throughout the conceptual,

basic and detailed engineering stages of new plants. Theguideline may also be used for modification projects ofexisting plants. When key operational parameters affecting thefire safety are to be modified on an existing plant, theprinciples in the guideline should be applied. It is important touse this guideline as early as possible in a project

development.The intention of the first version of the guideline was to

develop an effective design tool mainly based on adeterministic approach disregarding the fact that fire exposureof process plants is probalistic in nature.

The Guideline for Protection of Pressurized Systems

Exposed to Fire was first issued in 2002. It was madeavailable to the industry on the Scandpower web sitewww.scandpower.com.

The development of the guideline was funded by NorskHydro and Statoil. The guideline has been used by thesecompanies in development of new projects and modifications

to existing installations.In total nearly 400 persons have visited the web site and

downloaded the guideline.The responsible party for updating and maintaining the

guideline is Scandpower Risk Management AS in close co-operation with Norsk Hydro and Statoil.

Objective of the GuidelineThe objective of this guideline is to achieve a safe and costefficient design of pressurized systems that may be exposed tofire. This means a focus on fast depressurization instead ofusing passive fire protection (PFP). PFP is considered as an

effective measure that reduces the consequences of a fire.However, PFP also introduce problems relating to corrosion

and ultimately possible hydrocarbon leaks, reducedpossibilities for inspection, space and cost. The guidelinedirects the design to take full advantage of other measuressuch as proper material selection, pressure rating, wall

thickness etc. that may reduce the need for PFP. The guideline

SPE 86601

Optimizing Fire Protection of pressurized Process EquipmentJan Reier Huse,Scandpower Risk Management AS; Paul Skulstad Scandpower Risk Management AS;Bjrn Hekkelstrand; Scandpower Risk Mangement AS

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provides a procedure that may be applied and supportingbackground information pertaining to hydrocarbon firecharacteristics, material data and failure criteria.

The content of the guideline is divided into threemain parts.

- First part establish the main principles

- Second part discusses the key parameters- Third part introduces a specific procedure.

The application of this procedure is considered to result inadequate protection against realistic hydrocarbon fires. Asupplement to the procedure is to use a risk based approachfor the fire scenarios, the heat loads and acceptance criteria forrupture. It must be documented that the chosen solution is

within the risk acceptance criteria. This approach is notfollowed any further in the current version of the guideline.

Description of the guidelineThe guideline starts with establishing and discussing the main

principles for achieving an optimum fire protection of theprocess system. These are

- Maximum utilisation of the flare system- Selection of material quality- Selection of material thickness/pressure classes- Sizing of process segments/location of sectionalising

valves (inventory/volume)

- If necessary, application of passive fire protection- Active fire protection systems.

An illustration of the procedure outlined in the guideline isgiven by the flowchart presented in Figure 1.

The guideline has a strong focus on fast depressurisation inorder to meet the objective of minimized use of PFP, and thisis also reflected in the second part of the guideline thatdiscusses the key parameters of relevance.

- Depressurisation

- Passive fire protection- Deluge/water spray systems

- Pressure safety valves- Selection of process equipment/materials- Limitation of process inventories- Fire scenarios (dependent on layout, ventilation,

drainage, nature of combustible fluids, and nature ofrelease (time dependent leaks/duration)).

The third part of the guideline introduces a specificprocedure that should be applied for achieving an optimumfire protection. The procedure requires that rigorous

calculations should be performed including thermodynamics,heat and mass transfer etc. Figure 3 shows the detailed

iteration procedure that summaries the procedure.

System andscenario

information

Estimate sizeof

depressurizationorifice

Calculate P(t)for the process

segment and T(t)for the steel

Willequipment/pipe

rupture?

Failurecriteria

Are theconsequenceof the ruptureacceptable

?

Improvedesign/apply PFP

OK

Yes

YesNo

No

Isflare

capacityutilised

?

Yes

Increaseorifice size

No

Figure 1: Simplified Procedure for optimis ing Design of theDepressurising and Passive Fire Protection Systems for ProcessEquipment

The guideline discusses several hydrocarbon fire scenarios

that can occur and suggest typical initial incident heat fluxesto be used for the different fires (initial means toward a cold

segment). The proposed initial incident heat fluxes from jetfires are significantly higher (350 kW/m2) than earlier applied,at least by the Norwegian industry. The higher heat loading isjustified from the findings from recent years of fire research

on hydrocarbon fires in offshore like environments.The transient variation of the fire is of importance for jet

fires. The transient behaviour due to decreasing leak rates willboth influence the size of the fire exposed area, the total heatflux to the process segment and also the varying heat load toany specific point on the process segment. The guidelinediscusses and presents simplified formulas for calculation ofjet-fire duration from leaking segments with immediate or

delayed depressurisation. For a more accurate calculation ofjet-fire duration, a depressurisation simulation tool should beused.

The guideline refers and discusses acceptance criteria thatare widely used in offshore design in terms of:

- Hydrocarbon quantity that will be released as a result

of the rupture- Hydrocarbon leakage rates- Whether the released hydrocarbons are in gas or

liquid form- Pressure in the system at the time of the rupture (risk

of missiles, risk of critical damage to neighboring

pipe when a pipe bursts)- Location of the rupture compared to systems/

equipment/functions at risk- Risk of endangering personnel outside the immediate

vicinity of the area of the initial fire- Time to rupture.

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SPE 86601 3

The guideline focuses on minimising the use of PEP, i.e.the prime focus should be to design a depressurisation systemwith capacity to reduce the pressure in the system fast enough

to avoid critical escalation of the fire. The main concernsrelating to the use of PEP are increased corrosion of materialscovered by PEP, reduced possibilities for inspection andmaintenance of equipment covered with PEP, increased

weight, increased need for space, increased need formaintenance of the PEP and increased cost.

The guideline also focuses on the importance of keepingthe integrity of the flare system during a fire situation. Ruptureof parts of the flare system during a fire might result inmassive release of hydrocarbons (e.g. due to an ongoingdepressurisation) and, hence, cause a severe escalation of theaccident. If fire exposed, the flare piping is most vulnerable to

rupture just after start of depressurisation due to high massrates/highest pressure in the system. Delayed depressurisationshould therefore be avoided.

Further development of the Guideline

It was acknowledged early in the development of the guidelinethat although considerable efforts and large budgets have been

spent on research during the last years, there are still dark andgrey areas to be further investigated.

Figure 2illustrates some recognized issues that need furtherinvestigation. Some of these have materialized in ongoingresearch/test programs. Others will be addressed at alater stage.

Figure 2: Illustration of issues for further development ofthe Guideline

Large scale fire tests of flanged connectionsOne area of particular importance to the guideline is the

behavior of process piping systems exposed to high fire loads.Most efforts in this respect has been on the piping itself,whereas e.g. the flanged connections have been less focusedby the industry.

A research program was defined where the flanges inparticular were focused. The test program started in November

2003. As the tests are carried out at the time this paper iswritten, the results can not be included. The intention is topresent some result at the conference.

The flange connection is in the test exposed to a propan jetfire. The fire is designed to give a high heat loading (>250kw/m2), as uniform as possible over the test object. In order to

achieve this high heat loading the environment for the test isbased on the jet fire test procedure developed by theNorwegian Fire Research Laboratory.

The first part of the test program comprises a 10

pipesegment, with an ANSI RTJ flange connection beingexposed to the propane jet fire. The pipe segment is

pressurized to 150 barg with methane prior to the tests. Thepressure is maintained during the tests until an eventualleakage starts and continues as long as practicable possible.

The temperatures, pressures and displacements aremeasured in the pipe itself, flanges, and the bolts.

The first tests indicate that, when exposed to a gas-jet fire

a flange connection is a weak link in a piping system.The tests are carried out at Norwegian Fire Laboratory,

Trondheim, Norway.

Material tests

Another aspect is material behavior during fires. Most datafrom steel manufactures are verified through material testing

at ambient or relatively low temperatures compared tomaterial temperatures plausible in a fire situation (up to 1000-1100 deg C.). Material data for steel at temperatures above500 deg. C are normally not verified from representative tests.

The objective of the material testing is to establish reliablehigh temperature data (tensile strength and yield stress) for all

commonly used steel materials in the oil and gas industry.Material tests at elevated temperatures are on the program

for further research.The objective is to define material rupture criteria based on

material tests at temperatures that may occur during a

hydrocarbon fire.

Probabilist ic method for determining dimensioningfire scenariosThe current approach in the fire protection design is deter-ministic. A fire is defined as a jet fire or a pool fire, open orenclosed and then the ruleset of fire loads (heat flux values)

is applied.It is evident that for a plant, the maximum fire load will be

much higher than the average, and that there are arguments fornot always designing for the maximum.

Scandpower is developing a method for a probabilisticapproach to meet this design challenge. The method also

includes introduction of advanced simulation tools (CFD-codes) for prediction of heat loading and fire exposed areas

based on selected fire-scenarios.There are some parallels to the probabilistic methods now

being applied for explosion load determination. Thesemethods were developed as a necessity as it was evident that

there is not practicable possible to design against themaximum explosion pressure on typical large offshore

production installation.The probalistic fire analysis is subject to further

development by Scandpower Risk Management. Thisdevelopment is funded by Statoil and Scandpower Risk

Management.

Effect of deluge

water spray

Probabilistic

handling of fire

and leaka e

Acceptance

criteria for pipe

ru ture

Material

strength at high

tem erature

Flanged

connection

without PFP

The guideline version 1issued June 2002

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ConclusionThe guideline issued in 2002 provides a comprehensiveapproach for optimum fire protection of pressurized process

equipment. The guideline introduces a specific procedure fordesign of fire protection with focus on fast depressurization asa key factor for minimizing the need for PFP.

The guideline realize that there are lack of knowledge on

several topics, and has therefore initiated research programsand testing to start closing these gap. Large scale fire

experiments are carried out to determine the effect on flangedconnections under realistic conditions. Material data at hightemperatures will be established through material testing infire situations.

The guideline is under continuous development, and whennew knowledge is available new versions will be issued.

Results from experiments will be implemented in newversions.

References/1/ ISO 13702: "Petroleum and Natural Gas Industries - Control

and Mitigation of Fires and Explosions on Offshore Production

Installations - Requirements and Guidelines", 1999.

/2/ Norsk Hydro: "Best Practice Depressurization and Fire ReliefDesign", NHT-0101512, December 2001

/3/ NORSOK Standard S-001: "Technical Safety", Rev. 3, January2000.

/4/ ASME VIII: "Boiler and Pressure Vessel Codes".

/5/ NPD: "Forskrift om utforming og utrasting av innretninger medmer i petroleumsvirksomheten (Innretningsforskriften)",

3 September 2001.

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SPE 86601 5

Reduse the sizeof the orifice

Is theblowdown rate less

than maximumI-dP/dt.I

Is the flaresystem capacity

utilized (when adding all of thesimultaneous blowdown

rates together)?

Step 2:

Evaluate to increase the depres-surisation rate, preferrably for themost hazardous process segment.

Step 2:

Add insulation if required. Calculate the processsegment pressure profile. Use the fire with largestheat input (kW).Tip: Do several calculations with varying amountof fire insulation.

Step 8:

Calculate the wall temperature profile for all pipesand equipment.Use the local peak heat load (kW/m2).

Step 3:

Use the temperature profiles from step 3 to calculate the rupture

pressure for all pipes and equipment.Compare with the pressureprofile from step 1 or 8.

Step 4:

Estimate the size of all orifices and calculate thepressure profile and flare rates for all segments.Use the global average heat load with the largestheat input (kW). No PFP in this initial iteration.

Step 1:

- Pipe burst pressure- Equipment burst pressure- Released flammable fluid at rupture- Time to rupture- No rupture

Acceptance cr iteri a:

Step 2:

Step 5:

Is theacceptance criteria

for rupturemet ?

Decide which pipe/equipment to fire insulate ORincrease orifice diameter if available capacity inthe flare system OR reduce system volume byrelocation of sectionalisation valves OR increasethe flare system capacity OR change materialquality OR increase wall thickness.

Step 6:

Step 7

Calculate the minimum design temperature ofthe blowdown section and the flare system tail pipe.

Is theminimum

design temperatureacceptable?

The design of this section's blowdown orifice and fire insulation requirements is finished

Define start depressurisationat a higher temperature(or change material).

Required information prior to depressurisat ion iteration

- Description of the fire scenarios (type of fire, duration, heat fluxes, size)- Process segment geometry (system volume, area, weight etc.)- Ultimate tensile strength at elevated temperature of materials in the process segment- Manual or automatic depressurisation, i.e. time delay for start of depressurisation- Acceptance criteria for rupture

YESNO

NO

YES

NO

YES

YES

NO

Step 2:

In caseof any ofthe "OR's"

Figure 3: Flowchart for specific pr ocedure for optimizing fireprotection of pr essurized sys tems exposed to fire