ERT 422/4 Piping and instrumentation diagram ( P&id )

1. ERT 422/4 Piping and instrumentation diagram (P&id) MISS. RAHIMAH BINTI OTHMAN (Email: rahimah@unimap.edu.my)

2. Fundamentals of Pressure Relief Devices

3. What is the Hazard? • Despite safety precautions … • Equipment failures • Human error, and • External events, can sometimes lead to … • Increases in process pressures beyond safe levels, potentially resulting in … • OVERPRESSURE due to a RELIEF EVENT

4. What are Relief Events? • External fire • Flow from high pressure source • Heat input from associated equipment • Pumps and compressors • Ambient heat transfer • Liquid expansion in pipes and surge

5. Potential Lines of Defense • Inherently Safe Design • Passive Control • Active Control • Low pressure processes • Overdesign of process equipment • Install Relief Systems

6. What is a Relief System? • A relief device, and • Associated lines and process equipment to safely handle the material ejected

7. Why Use a Relief System? • Inherently Safe Design simply can’t eliminate every pressure hazard • Passive designs can be exceedingly expensive and cumbersome • Relief systems work!

8. BIOREACTOR CONTROL SYSTEM

9. Pressure Terminology • MAWP • Design pressure • Operating pressure • Set pressure • Overpressure • Accumulation • Blowdown

10. Pressure Relief DevicesWhat’s coming • Basic terminology • Code requirements • Safety relief valves • Rupture discs

11. Pressure Terminology • Operating pressure • MAWP • Design pressure • Set pressure • Accumulation • Overpressure • Blowdown

12. Code Requirements General Code requirements include: • ASME Boiler & Pressure Vessel Codes • ASME B31.3 / Petroleum Refinery Piping • ASME B16.5 / Flanges & Flanged Fittings

13. Code Requirements • All pressure vessels subject to overpressure shall be protected by a pressure relieving device • Liquid filled vessels or piping subject to thermal expansion must be protected by a thermal relief device • Multiple vessels may be protected by a single relief device provided there is a clear, unobstructed path to the device • At least one pressure relief device must be set at or below the MAWP

14. Code Requirements Relieving pressure shall not exceed MAWP (accumulation) by more than: • 3% for fired and unfired steam boilers • 10% for vessels equipped with a single pressure relief device • 16% for vessels equipped with multiple pressure relief devices • 21% for fire contingency

15. Relief Design Methodology LOCATE RELIEFS CHOOSE TYPE DEVELOP SCENARIOS SIZE RELIEFS (1 or 2 Phase) CHOOSE WORST CASE DESIGN RELIEF SYSTEM

16. Locating Reliefs – Where? • All vessels • Blocked in sections of cool liquid lines that are exposed to heat • Discharge sides of positive displacement pumps, compressors, and turbines • Vessel steam jackets • Where PHA indicates the need LOCATE RELIEFS

17. Choosing Relief Types • Spring-Operated Valves • Rupture Devices CHOOSE TYPE

18. Conventional Type Spring-Operated Valves CHOOSE TYPE

19. Picture: Conventional Relief Valve Conventional Relief Valve CHOOSE TYPE

20. Balanced Bellows Type Spring-Operated Valves CHOOSE TYPE

21. Picture: Bellows Relief Valve Bellows Relief Valve CHOOSE TYPE

22. Pros & Cons:Conventional Valve • Advantages • Most reliable type if properly sized and operated • Versatile -- can be used in many services • Disadvantages • Relieving pressure affected by back pressure • Susceptible to chatter if built-up back pressure is too high CHOOSE TYPE

23. Pros & Cons:Balanced Bellows Valve • Advantages • Relieving pressure not affected by back pressure • Can handle higher built-up back pressure • Protects spring from corrosion • Disadvantages • Bellows susceptible to fatigue/rupture • May release flammables/toxics to atmosphere • Requires separate venting system CHOOSE TYPE

24. Rupture Devices • Rupture Disc • Rupture Pin CHOOSE TYPE

25. ConventionalMetal Rupture Disc CHOOSE TYPE

26. ConventionalRupture Pin Device CHOOSE TYPE

27. When to Use a Rupture Disc/Pin • Capital and maintenance savings • Losing the contents is not an issue • Benign service (nontoxic, non-hazardous) • Need for fast-acting device • Potential for relief valve plugging • High viscosity liquids CHOOSE TYPE

28. When to Use Both Types • Need a positive seal (toxic material, material balance requirements) • Protect safety valve from corrosion • System contains solids CHOOSE TYPE

29. Relief Event Scenarios • A description of one specific relief event • Usually each relief has more than one relief event, more than one scenario • Examples include: • Overfilling/overpressuring • Fire • Runaway reaction • Blocked lines with subsequent expansion • Developed through Process Hazard Analysis (PHA) DEVELOP SCENARIOS

30. Rupture Discs • A rupture disc is a thin diaphragm (generally a solid metal disc) designed to rupture (or burst) at a designated pressure. It is used as a weak element to protect vessels and piping against excessive pressure (positive or negative). • There are five major types available • Conventional tension-loaded rupture disc • Pre-scored tension-loaded rupture disc • Composite rupture disc • Reverse buckling rupture disc with knife blades • Pre-scored reverse buckling rupture disc

31. Rupture Discs • They are often used as the primary pressure relief device. • Very rapid pressure rise situations like runaway reactions. • When pressure relief valve cannot respond quick enough. • They can also be used in conjunction with a pressure relief valve to: • Provide corrosion protection for the PRV. • Prevent loss of toxic or expensive process materials. • Reduce fugitive emissions to meet environmental requirements.

32. Rupture Discs Are Well Suited For Some Applications When compared with PR valves, rupture discs have: Advantages • Reduced fugitive emissions - no simmering or leakage prior to bursting. • Protect against rapid pressure rise cased by heat exchanger tube ruptures or internal deflagrations. • Less expensive to provide corrosion resistance. • Less tendency to foul or plug. • Provide both over pressure protection and depressuring. • Provide secondary protective device for lower probability contingencies requiring large relief areas.

33. Rupture Discs Are Less Well Suited For Other Applications When compared with PR valves, rupture discs have: Disadvantages • Don’t reclose after relief. • Burst pressure cannot be tested. • Require periodic replacement. • Greater sensitivity to mechanical damage. • Greater sensitivity to temperature

34. Conventional Tension-Loaded Metal Rupture Disc

35. Pre-Scored Tension - Loaded Rupture Disc

36. Disc Corroded Through

37. Composite Rupture Disc

38. Reverse Buckling Rupture Disc With Knife Blades

39. Typical RD/PRV Installation

40. Anything wrong here?

41. Pressure above RD Reduced inlet piping

42. Damaged during Installation

43. Classic Alligatoring

44. Conventional Rupture Pin Device

45. VALVES & PIPE SIZING

46. Sizing Reliefs • Determine relief vent area • Determining relief rates • Determine relief vent area SIZE RELIEFS (Single Phase)

47. LiquidService where Determine Relief Vent Area • A is the computed relief area (in2) • Qv is the volumetric flow thru the relief (gpm) • Co is the discharge coefficient • Kv is the viscosity correction • Kp is the overpressure correction • Kb is the backpressure correction • (r/rref) is the specific gravity of liquid • Ps is the gauge set pressure (lbf/in2) • Pb is the gauge backpressure (lbf/in2) SIZE RELIEFS (Single Phase)

48. GasService where Determine Relief Vent Area • A is the computed relief area (in2) • Qm is the discharge flow thru the relief (lbm/hr) • Co is the discharge coefficient • Kb is the backpressure correction • T is the absolute temperature of the discharge (°R) • z is the compressibility factor • M is average molecular weight of gas (lbm/lb-mol) • P is maximum absolute discharge pressure (lbf/in2) • c is an isentropic expansion function SIZE RELIEFS (Single Phase)

49. GasService where Determine Relief Vent Area • c is an isentropic expansion function • g is heat capacity ratio for the gas • Units are as described in previous slide SIZE RELIEFS (Single Phase)