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Working together for a safer world Process Safety and Risk Management Lecture 2 Håkon Dahl-Olsen Team Manager / Senior Consultant Technical safety, reliability.

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Presentation on theme: "Working together for a safer world Process Safety and Risk Management Lecture 2 Håkon Dahl-Olsen Team Manager / Senior Consultant Technical safety, reliability."— Presentation transcript:

1 Working together for a safer world Process Safety and Risk Management Lecture 2 Håkon Dahl-Olsen Team Manager / Senior Consultant Technical safety, reliability and flow assurance Lloyd's Register Consulting NTNU – Spring 2014

2 ©Lloyd’s Register Consulting Process Design – Protection of Life and Assets 100 persons on board – build cost ~ USD 2 Billion Foto: Håkon Dahl-Olsen © 2012

3 ©Lloyd’s Register Consulting Lecture 2 Pressure vessels API recommended protection Why blowdown? Blowdown under isothermal conditions Blowdown during fire Compressors API recommended protection What is compressor surge? How do we calculate settle-out pressure? Pumps How to read a pump curve Protection arrangement Risk analysis HAZOP Quantitative risk analysis in practice

4 ©Lloyd’s Register Consulting Separator Identify risks: -High pressure? -High level? -Low level? -High temperature? - Low temperature? -Etc.. Identify risks: -High pressure? -High level? -Low level? -High temperature? - Low temperature? -Etc..

5 ©Lloyd’s Register Consulting Separators and scrubbers API RP 14C

6 Separator Protection (Pressure Vessel) Pressure Safety Valve BDV Pressure trip No XV on this line? Early Design P&ID – Currently in operation in the UK

7 ©Lloyd’s Register Consulting 5.9 ”Gas blow-by”

8 ©Lloyd’s Register Consulting 5.10 Protection of separators Independence of barriers different operating principles (e.g. PTHH and PSV) each barrier should be able to do the job Gas blowby Note 1: Selection of upstream pressure for sizing of PSV Note 2: Flow through LV bypass Risk of common mode failures measurement principles for LIC and LTHH wax, hydrates, asphalthenes, foaming, etc.

9 5.11 Protection of separators Avoid cascade Dimensioning cases for PSVs fire blocked outlet failure of inflow control others >> NOTE: Test separator

10 Fire in process area - what happens? Medium inside steel vessel is heated up Pressure increases Strength of steel is decreased Question: How much energy is released if 100 m3 of gas at 80 bar is burned? Heat of combustion pr kg of a typical process gas is 1000 BTU/std. cu. ft. 55 GJ/ton Density of ideal gas: ρ = p M w / RT Do the math – the result is a lot of energy – about the explosion of 50 tons of TNT Worst incident on North Sea: Piper Alpha – 168 people were killed Question: How much energy is released if 100 m3 of gas at 80 bar is burned? Heat of combustion pr kg of a typical process gas is 1000 BTU/std. cu. ft. 55 GJ/ton Density of ideal gas: ρ = p M w / RT Do the math – the result is a lot of energy – about the explosion of 50 tons of TNT Worst incident on North Sea: Piper Alpha – 168 people were killed

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12 UTS strength and applied stress as function of temperature Increasing blowdown capacity

13 ©Lloyd’s Register Consulting Depressurization What should be depressurized: All hydrocarbon containing systems > 1000 kg (NORSOK S-001) For gas systems or unstabilized oil (high GOR) the limit should be significantly lower How fast?: (API RP 521: 7 bar within 15 min – considered obsolete requirement) PSA: as fast as possible NORSOK: as fast as possible to avoid escalation NORSOK: automatic activation in case of confirmed fire Fast depressurization should be prioritized over passive fire protection Does a PSV help you in case of a fire? Answer: Not much

14 Blowdown The problem set to be handed in treats this topic in detail Functionality of blowdown system explained on blackboard Modeling equations just for concept – will require coupled mass- and energy balances Specialized software modules used for detailed design (HYSYS Depressurization, Vessfire, OLGA)

15 Simplified modeling of blowdown Tank is 200 m3 and 50% filled. Pressure is 20 barg and temperature is 50 C. How long does it take to depressurize to 7 barg if the temperature is constant? The blowdown orifice can be taken as 12 mm in diameter. You may assume a gas molecular weight of 20 kg/kmol.

16 ©Lloyd’s Register Consulting Discrete modeling approach (forward Euler) 1. Specify mass, volume, temperature, pressure, molecular weight 2. Calculate density using ideal gas law ρ = p x MW / (RT) 3. Check for choked flow 1. Calculate flowrate (choked or subsonic) Q 4. Remaining mass in system after Δt: m(new) = m(old) - ρQ Δt 5. Calculate density using definition: ρ = m(new) / volume 6. Calculate new pressure using ideal gas law: p = ρ / (RT x MW) 7. Repeat from 3 Vaporization effect neglected – some pressure maintained by flashing This effect may be dimensioning for fires where there is extensive heat input! Vaporization effect neglected – some pressure maintained by flashing This effect may be dimensioning for fires where there is extensive heat input!

17 Excel Calculation Actual Design Tools: HYSYS Depressurisation utility Vessfire (more accurate for fire – made by company Petrell, head office in Trondheim)

18 ©Lloyd’s Register Consulting Recommended method: Lloyd's Register Consulting’s Guideline Referred to from NORSOK S-001 (Technical Safety) Generally accepted in industry Free download from Will be included as preferred method in API Std 521 (American Petroleum Institute) in next revision Developed in cooperation with Statoil and Hydro

19 ©Lloyd’s Register Consulting 6.1 Compression systems

20 ©Lloyd’s Register Consulting 6.2 Protection of compressors API 14C:

21 ©Lloyd’s Register Consulting 6.3 Protection of compressors Overpressure PTHH + PSV depending on compressor type evaluation of maximum pressure, suction pressure, compressor curve, mol weight, etc High temperature Liquid (– upstream scrubber) Equipment protection Depressurization may be dependent on sealing system Backflow ”Settle out” pressure

22 ©Lloyd’s Register Consulting 6.4 Protection of compressors

23 ©Lloyd’s Register Consulting 6.5 Protection of compressors

24 ©Lloyd’s Register Consulting 6.6 Protection of compressors Barriers against increased "settle out pressure" A number of solutions can be found NORSOK P 100: PSV dimensioned for leakage in check valve (1 % of pipe area)

25 ©Lloyd’s Register Consulting 6.7 Protection of compressors Liquid in compressor/overfilling of scrubber Seal systems, depressurization, etc Reciprocating compressors Vibration/pulsations Noise PSV capacity

26 ©Lloyd’s Register Consulting Pump Terminology Head (independent of fluid density): H = Δp/ρg (m or ft) NPSH (net pressure suction head): NPSH = (p in – p sat )/ρg Required NPSH is a property of the pump The NPSH must be above the required NPSH to avoid cavitation Centrifugal pump (rotating impeller) Piston pump (reciprocating piston – can create ”infinite” pressure)

27 Connecting the terms – pump curves

28 ©Lloyd’s Register Consulting 8.1 Protection of pumps API RP 14C:

29 10.2

30 ©Lloyd’s Register Consulting 8.2 Protection of pumps Overpressure Backflow Location of spec breaks Overheating Leaks

31 8.3 Protection of pump systems Alternative 2 Alternative 1

32 ©Lloyd’s Register Consulting

33 9.1 Texas City

34 9.3 Texas City

35 ©Lloyd’s Register Consulting 9.4 Summary/conclusion – Texas City Main causes of the accident and the extent of damage: Lack of focus on risk of major accidents (e.g. high no. of personnel and several potential ignition sources close to the ISOM unit) Lack of understanding of the process dynamics No automatic actions on critical process conditions Repeated, serious violations of the start-up procedure Lack of testing of critical equipment/instruments prior to start-up Low focus and many disturbances during start-up period Degraded safety culture – in particular process safety (focus on lost time incidents)

36 ©Lloyd’s Register Consulting HAZARD AND OPERABILITY STUDY (HAZOP)

37 ©Lloyd’s Register Consulting Advantages of HAZOP Thorough and systematic review Many diciplines, roles and parties are represented Funded on operational experience Takes operational procedures into account Takes human mistakes into account ”Studpid” questions are allowed – as a consequence important problem areas can be identified

38 Background and purpose of HAZOP Why HAZOP? HAZOP reviews are one of several methods with the purpose of identifying hazards and elements of risk related to planned operations, and to identifiy risk reducing measures.

39 Introductory example from BP Texas accident – Poor control of risk contributors – in this case: oil and gas leaks Oil and gas leaks are significant risk contributors Leaks may occur due to technical failure and/or erroneous operation Leaks can be prevented through: Good design and construction Checked in HAZOP Inspection and maintenance Correct use of procedures Checked in HAZID Effective communication Competent personnel Invariable safety rules

40 ©Lloyd’s Register Consulting Overview of method and application HAZOP – HAZard and OPerability analysis Identification of possible maloperations or malfunctions of system units and possible consequences for personnel, environment or assets Is often based on the plant / system’s "Piping and Instrument Diagrams - P&IDs" or operational procedures for critical activities

41 ©Lloyd’s Register Consulting Overview of method and application Purpose The superior purpose of HAZOP is to reduce risk for personnel, environment and assets. To identify possible safety or operational problems that can occur during operation or maintenance of the processing plant. The primary goal is to reveal possible problems. Suggestions for improvements are documented (but not discussed)

42 ©Lloyd’s Register Consulting Overview of method and application Application HAZOP must be performed sufficiently early, to be able to influence design or planning late, to enable gathering of adequate documentation to be used as a basis for the HAZOP The method is generic and can be used on all types of systems / procedures / plants. Some adaptations may be needed

43 Method – preparation / implementation General What can go wrong?

44 24 inches in diameter floating load hose on the FPSO Girassol in Angola, Africa that was pierced by a blue marlin.

45 GUIDEWORDS: NO / NOT MORE (HIGHER) LESS (LOWER) AS WELL AS PART OF REVERSE OTHER THAN PARAMETERS: PRESSURE TEMPERATURE FLOW LEVEL COMPOSITION CONTAMINATION MAINTENANCE REACTION AD-/ABSORPTION Guidewords / parameters PROCESS-HAZOP

46 Choose node Choose parameter / guideword Identify cause and consequence Identified hazardDocument All parameters / Guidewords covered All nodes covered All systems covered No Yes

47 Example: liquid-gas separator

48 ©Lloyd’s Register Consulting QRA – Quantitative Risk Analysis

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50 Process Accident Modeling

51 Output ExploRAM

52 ©Lloyd’s Register Consulting Event tree Leak frequencyIgnition?Major explosion? Final event Unignited leak Fire Explosion Frequency of final event Consequences Loss of life Escape routes

53 Lloyd’s Register and variants of it are trading names of Lloyd’s Register Group Limited, its subsidiaries and affiliates. Copyright © Lloyd’s Register Consulting A member of the Lloyd’s Register group. Working together for a safer world Håkon Dahl-Olsen Senior Consultant / Team Manager Technical safety, reliability and flow assurance T E Lloyd’s Register Consulting


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