API 576 Exer ci ses Pressure Relief Devices Descriptions Instructions : Read Read API 576 576 from its beginnin g and as you find the answers to the questions below enter th em. For the Sectio n VIII quest ion s read p aragraphs UG-125 UG-125 to UG-12 UG-128 8 Pressure Relief Valves 1.
A pressure relief device is actuated by ___________________________.
2.
All pressure vessels other than unfired steam boilers shall be protected protected by a pressure relief device that shall prevent the pressure from rising more than _____or ____, whichever is greater, above the maximum allowable working pressure.
3. Safety, safety relief, and relief valves shall be of the ____________ loaded type. 4.
The set pressure tolerances, plus or minus, of pressure relief valves shall not exceed __________ for pressures up to and including 70 psi (483 kPa) and ___% for for pressures above 70 psi (483 kPa).
5.
A _________valve is a pressure relief valve characterized by rapid opening or pop action or by opening in proportion to the increase in pressure over the opening pressure, depending on application.
6.
The spring spring of a _______ valve is usually fully exposed.
7. Relief valves usually reach full lift at either _____% or____% or____% overpressure, depending on the the type of valve and trim. 8. A safety relief valve is normally fully open at ____% over-pressure when in gas or vapor service. 9. A __________ safety relief valve has a bonnet that encloses the spring and forms forms a pressurepressuretight cavity. The bonnet cavity is vented to the discharge side of the valve. 10. The pressure at which a pressure relief valve is adjusted to open on the test stand is known as the ________. 11. Balanced safety relief valves are normally used in refinery and petrochemical process industries that handle flammable, hot, or toxic material, where____________ are present at the valve discharge. 12. A ______________safety relief valve is a pressure relief valve in which the major relieving device or main valve is combined with and controlled by a self actuated auxiliary pressure relief valve. 13. Pressure and/or vacuum vent valves are normally used to protect __________ and _____________storage tanks against a pressure pressure large enough to damage the tank. tank.
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API 576 Exer ci ses Rupture Disks 14. The burst pressure tolerance at the specified rupture disk temperature shall not exceed ±_______for marked burst pressure up to and including 40 psi (276 kPa) and ±___% for marked burst pressure above 40 psi (276 kPa). 15. The combination of a rupture disk holder and rupture disk is known as a _________________. 16. A conventional domed rupture disk is a ___________solid metal disk designed to burst when it is over-pressured on the __________side. 17. Scored Tension-Loaded Rupture Disk designed to allow a _________ of system operating pressure to disk burst pressure. 18. ________________rupture disks are designed to open by such methods as shear, knife blades, knife rings, or scored lines 19. ____________ are intended to be used as corrosion barriers only. 20. Graphite rupture disks _______upon rupture; provisions for ____________may be required in certain applications. 21. Rupture disk devices are sometimes used if ______________ response is desirable. 22. The proper receipt, storage, handling, and installation of a rupture disk are critical to its successful performance. Refer to the manufacturer's installation instructions, especially those concerning _________________. 23. Since rupture disks are designed to burst at a specified differential pressure, pressure build up on the _____________side of the disk may inhibit the disk's ability to provide overpressure protection. 24. When a rupture disk device is used with a pressure relief valve, consult the ___________for the capacity reduction and installation details. 25. UG-127 of the ASME Code states that a rupture disk device may be used as the _______pressure relieving device on a vessel. 26. The service life of pre-bulged metal rupture disks under normal operating conditions is usually __________. 27. One of the limitations of rupture disks is that if not replaced periodically they may _________________at normal operating pressures. 28. Rupture disks that tend to fragment, such as ________and_________ disks are typically not installed beneath pressure relief valves unless a means of protecting the pressure relief valve inlet from the fragments is provided.
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API 576 Exer ci ses Causes o f Improper Performance 29. ________is a basic cause of many of the difficulties encountered with pressure relief devices. 30. The use of an ______ seat in a pressure relief valve will sometimes stop leakage past the seating surface and eliminate corrosion in the valve's working parts. 31. Because differential loading must be small to prevent leakage of the lading fluid, an optical precision on the order of ________ must be maintained in the flatness of seating surfaces on metal-seated pressure relief valves. 32. Leakage contributes to seat damage by causing _________ or corrosion of the seating surface and thus aggravating itself. 33. Although springs may weaken and fail due to the use of improper materials in high temperature service, failed springs are almost always caused by ____. 34. _________corrosion cracking sometimes causes rapid spring failure. 35. Setting a pressure relief valve while it is in place on the equipment to be protected may be impractical and should be performed only after _______ ___________. 36. Vapor service valves should be set using _____ or_________. 37. __________on pressure gauges used to set pressure relief valves are not generally recommended since they tend to clog and produce pressure lag. 38. Sticking of valves can also result from machining of valve parts outside the _________________________ limits. 39. Foreign particles in the guiding surfaces of a relief valve tend to roll metal up, causing severe galling. The use of a ________can keeps the foreign particles away from the guiding surfaces. 40. When galling of the metal in the guiding surfaces is not due to corrosion or foreign particles, it is often due to _______ or _______ caused by improper piping at the valve inlet or outlet or by severe over sizing of the valve. 41. Some users stamp ________________ with device numbers. This identification specifies the location of the valve and, by reference to the specification record, its l imitations and construction. 42. Rough handling can occur during _______, _______ or ___________. 43. Because of their operation, most pressure relief valves have a sturdy appearance that may obscure the fact that they are ____________with very cl ose tolerances and sensitive dimensions. 44. Careful handling of the valve during all phases of maintenance is important. Both before and after repairs, rough handling of the completely assembled valve should be avoided. Before the valves leave the shop, valve _____ and ____ should be __________. 45. The bellows of a balanced relief valve may be damaged by excessive back pressure during a _____________ test.
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API 576 Exer ci ses Inspection and Testing 46. During a shop inspection since the device is removed __________ should be inspected for the presence of internal deposits and records should be kept of their condition. 47. Some pressure-relieving valves have set pressures that exceed their _________.
48. As a safety precaution before disconnecting pressure-relieving devices, the connected piping and block valves should be checked to ensure that they are _______________________________. 49. If there is a rupture disk device associated with the pressure relief valve and the rupture disk device is disturbed as part of the accompanying relief valve removal, consider the need to ____________________________. 50. When block valves are used with a relief device, these block valves must have __________________________________and possible instability when the relief device opens. 51. It is usually impossible to inspect inlet and outlet piping of a relief device while it is in service; before it is taken out of service________________ can indicate major fouling or stoppage. 52. During a visual the__________, should be inspected for evidence of pitting, roughening, or decreases in the width of seating surfaces. 53. At each stage in the pressure relief device dismantling process, the various parts of the valve should be visually inspected for evidence of wear and corrosion. When unusual corrosion, deposits, or conditions are noted in the pressure relief valve, an _______________should assist in the inspection. 54. At each stage in the dismantling process, the various parts of the valve should be visually inspected for evidence of _________and corrosion. 55. Bellows should be checked for leaks, cracks, or thin spots that may develop into leaks. In addition, if the bellows has collapsed, it has probably been subjected to ______________________ greater than its design pressure. 56. Because most test blocks do not have enough _________ to measure the actual blow down, manufacturer’s recommendations and past performance should be evaluated to estimate any necessary adjustment. 57. Once the relief valve is set to pop at its CDTP, it should be checked for______. 58. All necessary _______ should be __________ before a valve is placed back into service. 59. When a relief valve operates in __________service, experience may indicate that inspection of the valve while on the equipment is safe. 60. _____________rupture disks may be used to facilitate and allow more frequent on-stream testing of pressure relief valves. 61. The ASME Section I Code requires the boiler safety valves have a substantial lifting device by which the valve disk may be lifted from its seat when the working pressure on the boiler is at least ______% of the set pressure. 62. Inspection, testing, maintenance, and setting of the pilot mechanism may be ___________________from the main valve.
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API 576 Exer ci ses
63. A visual on-stream inspection is more like a __________ than a normal inspection and may be considered a control measure. 64. The ideal time to inspect pressure relief valves is when the inspection least ________ with the process and maintenance manpower is readily available. 65. A pressure relief valve left on a unit during an extended shutdown should be inspected and ______before the resumption of operations. 66. Pressure and/or vacuum vent valves are in almost continuous service. They are prone to failure by _______________. 67. If a disk's manufacturer specifies a bolting torque procedure and the tightened bolts are loosened, the rupture disk should be replaced. Do not reinstall the disk once it has been removed from its holder, even though it has n ot been ruptured. When stresses are relieved by unbolting, the “____” taken by the disk during its original installation may prevent a tight seal and affect performance if reinstalled. 68. Because they ________________, rupture disks should be replaced on a regular schedule based on their application, the manufacturer's recommendations, and past experience. Records and Reports
69. Records may be considered as tools needed to implement the program, and reports may be considered as the _______________________________________ to all the participants of the program so that they coordinate their work and effectively discharge their responsibilities. 70. For each pressure-relieving device in service, a complete, permanent record should be kept. The record of each device should include its ______________________, and a continuously accumulating history of inspection and test results. 71. The precise _____________ and ________________ format in a pressure relieving device program is a matter of individual company choice.
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API 576 ANSWERS Pressure Relief Devices Descriptions Pressure Relief Valves 1. A pressure relief device is actuated by inlet static pressure. (4.0) 2.
All pressure vessels other than unfired steam boilers shall be protected by a pressure relief device that shall prevent the pr essure from rising more than 10% or 3 psi, whichever is greater, above the maximum allowable working pressure. (UG-125 (c) )
3. Safety, safety relief, and relief valves shall be of the direct spring loaded type. 4. The set pressure tolerances, plus or minus, of pressure relief valves shall not exceed 2 psi (13.8 kPa) for pressures up to and including 70 psi (483 kPa) and 3% for pressures above 70 psi (483 kPa). (UG-126 (d) ) 5.
A safety relief valve is a pressure relief valve characterized by rapid opening or pop action or by opening in proportion to the increase in pressure over the opening pressure, depending on application. (4.2)
6.
The spring of a safety valve is usually fully exposed. (4.2)
7. Relief valves usually reach full lift at either 10% or 25% overpressure, depending on the type of valve and trim. (4.3) 8. A safety relief valve is normally fully open at 10% over-pressure when in gas or vapor service. (4.4) 9. A conventional safety relief valve has a bonnet that encloses the spring and forms a pressuretight cavity. The bonnet cavity is vented to the discharge side of the valve. (4.5) 10. The pressure at which a pressure relief valve is adjusted to open on the test stand is known as the Cold Differential Test Pressure (CDTP). (3.4.7) 11. Balanced safety relief valves are normally used in refinery and petrochemical process industries that handle flammable, hot, or toxic material, where high back pressures are present at the valve discharge. (4.6.1) 12. A pilot-operated safety relief valve is a pressure relief valve in which the major relieving device or main valve is combined with and controlled by a self actuated auxiliary pressure relief valve. (4.7) 13. Pressure and/or vacuum vent valves are normally used to protect atmospheric and low-pressure storage tanks against a pressure large enough to damage the tank. (4.8)
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API 576 ANSWERS Rupture Disks 14. The burst pressure tolerance at the specified rupture disk temperature shall not exceed ± 2( 13.8 kPa) psi for marked burst pressure up to and including 40 psi (276 kPa) and ± 5% for marked burst pressure above 40 psi (276 kPa). 15. The combination of a rupture disk holder and rupture disk is known as a rupture disk device. (4.9) 16. A conventional domed rupture disk is a pre-bulged solid metal disk designed to burst when it is over-pressured on the concave side. (4.9.1.1) 17. Scored Tension-Loaded Rupture Disk designed to allow a closer ratio (generally 85%) of system operating pressure to disk burst pressure. (4.9.1.2) 18. Reverse acting rupture disks are designed to open by such methods as shear, knife blades, knife rings, or scored lines. (4.9.1.4) 19. Composite rupture disks are intended to be used as corrosion barriers only. (4.9.1.3) 20. Graphite rupture disks fragment upon rupture; provisions for capturing the fragments may be required in certain applications. 21. Rupture disk devices are sometimes used if extremely fast response is desirable. (4.9.2) 22. The proper receipt, storage, handling, and installation of a rupture disk are critical to its successful performance. Refer to the manufacturer's installation instructions, especially those concerning limits on bolt torque. (4.9.2) 23. Since rupture disks are designed to burst at a specified differential pressure, pressure build up on the down-stream side of the disk may i nhibit the disk's ability to provide overpressure protection. (4.9.2) 24. When a rupture disk device is used with a pressure relief valve, consult the ASME Code for the capacity reduction and installation details. (4.9.2) 25. UG-127 of the ASME Code states that a rupture disk device may be used as the sole pressure relieving device on a vessel. (UG-127) 26. The service life of pre-bulged metal rupture disks under normal operating conditions is usually one year. (4.9.3) 27. One of the limitations of rupture disks is that if not replaced periodically they may they may fail without warning at normal operating pressures. (4.9.3) 28. Rupture disks that tend to fragment, such as conventional and graphite disks are typically not installed beneath pressure relief valves unless a means of protecting the pressure relief valve inlet from the fragments is provided. (4.9.3)
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API 576 ANSWERS Causes of Improper Performance 29. Corrosion is a basic cause of many of the difficulties encountered with pressure relief devices. (5.1) 30. The use of an O-ring seat in a pressure relief valve will sometimes stop leakage past the seating surface and eliminate corrosion in the valve's working parts. (5.1) 31. Because differential loading must be small to prevent leakage of the lading fluid, an optical precision on the order of 3 light beads/bands must be maintained in the flatness of seating surfaces on metal-seated pressure relief valves. (5.2) 32. Leakage contributes to seat damage by causing erosion (wire drawing) or corrosion of the seating surface and thus aggravating itself. (5.2) 33. Although springs may weaken and fail due to the use of improper materials in high temperature service, failed springs are almost a lways caused by corrosion. (5.3) 34. Stress corrosion cracking sometimes causes rapid spring failure. (5.3) 35. Setting a pressure relief valve while it is in place on the equipment to be protected may be impractical and should be performed only after special consideration as noted in 6.2.2.18. (5.4) 36. Vapor service valves should be set using air or inert gas. (5.4) 37. Snubbers on pressure gauges used to set pressure relief valves are not generally recommended since they tend to clog and produce pressure lag. (5.4) 38. Sticking of valves can also result from machining of valve parts outside the manufacturers tolerance limits. (5.5) 39. Foreign particles in the guiding surfaces of a relief valve tend to roll metal up, causing severe galling. The use of a bellows can keeps the foreign particles away from the guiding surfaces. (5.5) 40. When galling of the metal in the guiding surfaces is not due to corrosion or foreign particles, it is often due to valve chatter or flutter caused by improper piping at the val ve inlet or outlet or by severe over sizing of the val ve. (5.5) 41. Some users stamp mating pipe flanges with device numbers. This identification specifies the location of the valve and, by reference to the specification record, its l imitations and construction. (5.7) 42. Rough handling can occur during shipment, maintenance or installation. (5.8) 43. Because of their operation, most pressure relief valves have a sturdy appearance that may obscure the fact that they are delicate instruments with very close tolerances and sensitive dimensions. (5.8.1) 44. Careful handling of the valve during all phases of maintenance is important. Both before and after repairs, rough handling of the completely assembled valve should be avoided. Before the valves leave the shop, valve inlets and outlets should be covered. (5.8.1) 45. The bellows of a balanced relief valve may be damaged by excessive back pressure during a hydrostatic test. (5.10)
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API 576 ANSWERS Inspection and Testing 46. During a shop inspection since the device is removed inlet and outlet piping should be inspected for the presence of internal deposits and records should be kept of their condition. (6.2) 47. Some pressure-relieving valves have set pressures that exceed their outlet flange rating. (6.2.1) 48. As a safety precaution before disconnecting pressure-relieving devices, the connected piping and block valves should be checked to ensure that they are sufficiently supported. (6.2.1) 49. If there is a rupture disk device associated with the pressure relief valve and the rupture disk device is disturbed as part of the accompanying relief valve removal, consider the need to install a new rupture disk. (6.2.4) 50. When block valves are used with a relief device, these block valves must have full pipe area through them to prevent restriction and possible i nstability when the relief device opens. (6.2.4) 51. It is usually impossible to inspect inlet and outlet piping of a relief device while it is in service; before it is taken out of service radiographs can indicate major fouling or stoppage. (6.2.6) 52. During a visual the flanges, should be inspected for evidence of pitting, roughening, or decreases in the width of seating surfaces. (6.2.9) 53. At each stage in the pressure relief device dismantling process, the various parts of the valve should be visually inspected for evidence of wear and corrosion. When unusual corrosion, deposits, or conditions are noted in the pressure relief valve, an inspector should assist in the inspection. (6.2.10) 54. At each stage in the dismantling process, the various parts of the valve should be visually inspected for evidence of wear and corrosion. (6.2.10) 55. Bellows should be checked for leaks, cracks, or thin spots that may develop into leaks. In addition, if the bellows has collapsed, it has probably been subjected to back pressure greater than its design pressure. (6.2.10) 56. Because most test blocks do not have enough capacity to measure the actual blow down, manufacturer’s recommendations and past performance should be evaluated to estimate any necessary adjustment. (6.2.13) 57. Once the relief valve is set to pop at its CDTP, it should be checked for leakage. (6.2.15) 58. All necessary records should be completed before a valve is placed back into service. (6.2.16) 59. When a relief valve operates in non-fouling service, experience may indicate that inspection of the valve while on the equipment is safe. (6.2.17) 60. Reverse-buckling rupture disks may be used to facilitate and allow more frequent on-stream testing of pressure relief valves. (6.2.17)
61. The ASME Section I Code requires the boiler safety valves have a substantial lifting device by which the valve disk may be lifted from its seat when the working pressure on the boiler is at least 75 % of the set pressure. (6.2.18) 62. Inspection, testing, maintenance, and setting of the pilot mechanism may be handled separately from the main valve. (6.2.19)
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API 576 ANSWERS
63. A visual on-stream inspection is more like a survey than a normal inspection and may be considered a control measure. (6.3) 64. The ideal time to inspect pressure relief valves is when the inspection least interferes with the process and maintenance manpower is readily avai lable. (6.5.1) 65. A pressure relief valve left on a unit during an extended shutdown should be inspected and tested before the resumption of operations. (6.5.4) 66. Pressure and/or vacuum vent valves are in almost continuous service. They are prone to failure by sticking. (6.2.20) 67. If a disk's manufacturer specifies a bolting torque procedure and the tightened bolts are loosened, the rupture disk should be replaced. Do not reinstall the disk once it has been removed from its holder, even though it has n ot been ruptured. When stresses are relieved by unbolting, the “ set ” taken by the disk during its original installation may prevent a tight seal and affect performance if reinstalled. (6.2.21) 68. Because they cannot be tested, rupture disks should be replaced on a regular schedule based on their application, the manufacturer's recommendations, and past experience. (6.2.21)
Records and Reports 69. Records may be considered as tools needed to implement the program, and reports may be considered as the means to distribute those tools needed to implement the program to all the participants of the program so that they coordinate their work and effectively discharge their responsibilities. (7.1) 70. For each pressure-relieving device in service, a complete, permanent record should be kept. The record of each device should include its specification data, and a continuously accumulating history of inspection and test results. (7.2) 71. The precise recording and reporting format in a pressure relieving device program is a matter of individual company choice. (7.4)
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