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2A2-5: Testing of Metals > Objective 11: Leak and Pressure Testing > Flashcards

Objective 11: Leak and Pressure Testing Flashcards

1
Q

What is the purpose of Leak Testing?

A

To verify the integrity of a completed pressure vessel or fitting before it is placed into service or to determine if a vessel currently in service may continue to be used

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2
Q

What does Leak Testing identify?

A

Discontinuities in the vessel pressure boundary

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3
Q

What is the minimum test pressure to be used in Pressure Testing?

A

1.25 - 1.3x the MAWP

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4
Q

Is Pressure Testing required to be carried out on completed boilers, PVs, and pressure piping?

A

Yes

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5
Q

What are the 2 purposes of Pressure Testing?

A
  1. Prove that the vessel can withstand the pressure for which it was designed
  2. To ensure no leaks are present
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6
Q

Why is Pressure Testing used on piping and vessels that have already been in service?

A

To verify that they can still safely withstand the operating pressure with a proven margin of safety and that no through cracks or holes have developed

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7
Q

When is Pressure Testing especially useful to be carried out?

A

When the Inspector does not have adequate access to conduct a visual inspection

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8
Q

Why do many jurisdiction inspectors and owners require the organization performing the Pressure Test to provide written test procedures?

A

Reviewing and approving these procedures prior to the test averts potential problems

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9
Q

What is the first step in leak testing?

A

To determine whether leaks are present

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10
Q

What are the 2 types of pressure tests are used to aid in the detection of a leak?

A
  1. Hydrostatic

2. Pneumatic

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11
Q

What is the basic process of Hydrostatic Testing?

A

The vessel is filled with water and the fluid is pressurized to the required pressure. The vessel is then examined for leaks

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12
Q

How is a New Vessel prepared for Hydrostatic Testing?

A
  1. All connections such as flanges and couplings are closed off with blind flanges and plugs
  2. A drain valve is located at the low point of the vessel to allow removal of the water right after the test
  3. The filling connection must have an isolating valve and a vent valve is required at the top to allow all air to be expelled
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13
Q

How is an In-Service Vessel prepared for Hydrostatic Testing?

A
  1. If the fluid the vessel normally handles is toxic or flammable, the vessel is cleaned and purged
  2. The vessel is isolated from the test of the system. Existing valves are used if they’re in good condition; otherwise piping connections at the vessel are opened and blind flanges are installed
  3. Control line connections to the vessel are removed and closed off
  4. Procedures for New Vessel are carried out
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14
Q

How is a Vessel that isn’t designed to hold water prepared for Hydrostatic Testing?

A

Additional supports may be required for the vessel and the foundation must be inspected to ensure it can carry the additional weight

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15
Q

How is the test pressure monitored during Hydrostatic Testing?

A

On a calibrated pressure gauge; 2 gauges may be used as an additional precaution

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16
Q

What is the most common fluid used for hydrostatic testing?

A

Water

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17
Q

Why is water the most common fluid used for Hydrostatic Testing?

A
  1. Inexpensive

2. Readily available

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18
Q

When should a glycol/water mixture or methanol be considered for Hydrostatic Testing?

A

When the test is performed with ambient conditions near or below freezing temperature

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19
Q

What is the benefit of using a glycol/water mixture or methanol for Hydrostatic Testing at or below freezing temperature?

A

Avoids the possibility of frozen drain lines when the test is completed

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20
Q

What are the cons of using a glycol/water mixture or methanol for Hydrostatic Testing?

A
  1. More expensive than water

2. Disposal poses environmental problems

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21
Q

What test pressure must be used when performing Hydrostatic Testing on Used Equipment?

A

The owner or jurisdiction inspector may determine the test pressure but it should not exceed the test pressure used for testing when the vessel was new. If the inspector is only condernced with leaks that may have developed in service, a hyrostatic test at the operating pressure is acceptable

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22
Q

What should be the temperature of the water used for Hydrostatic Testing of boilers?

A

Not less than ambient temperatures but in no case below 20ºC

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23
Q

Why is temperature a concern in Hydrostatic Testing?

A

To avoid brittle fracture

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24
Q

What temperature should the metal be maintained at during Hydrostatic Testing?

A

At least 17ºC above the minimum design metal temperature

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25
Q

During Hydrostatic Testing, what should be done to prevent burn hazards?

A

If the test temperature exceeds 48ºC, inspection of the vessel should be delayed until the temperature falls to 48ºC or less

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26
Q

Once the vessel is filled, how is the internal pressure increased during Hydrostatic testing?

A

Pump

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27
Q

In how many steps is pressure increased during Hydrostatic Testing?

A
  1. For LP test, 1

2. For HP test, several with visual inspection conducted at the end of each step

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28
Q

At what test pressure is it safe for the Inspector to inspect the vessel for leaks during Hydrostatic Testing?

A

Below 3000 kPa

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29
Q

What is dangerous about inspecting a vessel at a test pressure greater than 3000 kPa during Hydrostatic Testing?

A

Water jets issuing from a pinhole or crack

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30
Q

How is a vessel with a test pressure greater than 3000 kPa during Hydrostatic testing safely inspected?

A
  1. The vessel is pressurized to test pressure and held there for a specified time while the pressure gauges are observed
  2. The pressure is then reduced to the normal operating pressure before inspecting is done
31
Q

What does visual inspection of a vessel during Hydrostatic Testing entail?

A
  1. Examining the entire surface of the vessel for wet areas and small drops of liquid
  2. Looking for pressure drop during the Hydrostatic Test
32
Q

Why is a lack of pressure drop during Hydrostatic Testing not proof the vessel is leak free?

A
  1. A very small leak may not produce a noticeable pressure drop
  2. An increase in the temperature of the test liquid can create sufficient expansion to compensate for any losses due to leakage
33
Q

What is done after Hydrostatic Testing is complete?

A

Pressure is slowly released

34
Q

Why are liquids used for Hydrostatic Testing?

A

They do not expand significantly when pressure drops. If a failure occurs, only a small, harmless flow of water will be released.

35
Q

What are the advantages of Hydrostatic Testing?

A
  1. Inexpesive

2. Relatively easy to perform, provided the vessel is properly prepared

36
Q

Pneumatic Testing

A

Pressurization of a vessel or piping system with a compressible gas such as air or nitrogen to determine if any leaks are present

37
Q

Should Pneumatic Testing be a favoured NDE and why?

A

No because it may be hazardous

38
Q

Why is Pneumatic Testing resorted to?

A

The air or nitrogen may be the only suitable test substance if water can damage the interior of the vessel, e.g. refractory linings or catalyst beds

39
Q

What is the basic preparation for Pneumatic Testing?

A

Isolation of the vessel from the system and controls

40
Q

What is a benefit of using gas as the test medium as in Pneumatic Testing?

A

It does not place a significant amount of static head in the vessel

41
Q

When is air a suitable gas to be used in Pneumatic Testing and why?

A

For general applications due to it being inexpensive and readily available

42
Q

When is nitrogen a suitable gas to be used in Pneumatic Testing?

A

When a possibility of combustion exists

43
Q

Why do some codes allow Pneumatic Testing to use lower test pressures than Hydrostatic Testing?

A

The inherent danger in testing with compessed gases

44
Q

When is a test pressure lower than operating pressure acceptable to be used in Pneumatic Testing?

A
  1. The Pneumatic Test is used as an additional test to the Hydrostatic Test
  2. The Pneumatic Test is used as a leak test prior to the Hydrostatic Test
45
Q

How important is proper test temperature for Pneumatic Testing?

A

If there is any possibility of brittle failure of the test vessel, another method should be used

46
Q

How is the testing gas for Pneumatic Testing usually delivered to the test site?

A

As a liquid or at a very high pressure

47
Q

How is the required test pressure achieved for Pneumatic Testing?

A

Pressure reducing system

48
Q

What effect can pressure reduction have on the Vessel or Piping for Pneumatic Testing?

A

It can cool them enough to affect the ductility of the metal

49
Q

What is used to maintain a minimum gas temperature during Pneumatic Testing?

A

Heaters

50
Q

What precaution must be taken if the supply pressure of the test fluid is higher than the test pressure for Leak Testing?

A

Overpressure Protection

51
Q

How is test pressure increased during Pneumatic Testing?

A

In stages with inspection occurring at each stage

52
Q

What is the primary safety concern in Pneumatic Testing?

A

The amount of energy stored in the compressed fluid during the test means that is a failure occurs, the results can be catastrophic

53
Q

What are the advantages of Pneumatic Testing?

A
  1. At low pressures, the danger is reduced and leaks can be found by a soap test
  2. Does not create mass loading on the item being tested
  3. Doesn’t involve cleanup after the test because the gases can be vented to atmosphere
  4. May be the only acceptable test method in cases where the vessel interior is lined with material that liquids can damage
54
Q

If leaks have been determined by Leak Testing, what are the 9 different methods used to pinpoint their exact location?

A
  1. Bubble Test - Direct Pressure Technique
  2. Bubble Test - Vacuum Box Technique
  3. Halogen Diode Detector Probe Test
  4. Helium Mass Spectrometer - Detector Probe Technique
  5. Helium Mass Spectrometer - Tracer Probe and Hood Technique
  6. Pressure Change Test
  7. Thermal Conductivity Detector Probe Test
  8. Helium Mass Spectrometer Test - Hood Technique
  9. Ultrasonic Leak Detector Test
55
Q

What is another name for Bubble Test?

A

Soap Test

56
Q

When is Bubble Leak Testing used?

A

The pressurizing fluid is a gas and access is available to the surface where the leak is suspected

57
Q

What is the old procedure of the Bubble Leak Test?

A
  1. Liquid soap solution is brushed or poured over the pressurized vessel or piping system
  2. Escaping gas forms bubbles in the soap solution, providing a clealy visible indication of where a leak is occuring
  3. The number and size of bubbles indicates the size of the leak
58
Q

What is problematic about the old Bubble Leak Test?

A
  1. The soap leaves a film where it dries
  2. If hard water is used, the soap tends to curdle rather than bubble
  3. Impurities in water can sometimes contaminate the material being tested
59
Q

How does the new Bubble Leak Test differ from the old?

A

Instead of soap, special solutions with enhanced surface tension, viscosity, and film retention properties are used

60
Q

What is the benefit of the new Bubble Leak Test?

A

The solution enables Inspectors to locate smaller leaks than is possible when using soap and water

61
Q

Immersion Bubble Leak Testing

A

A more inolved method of bubble testing that involves placing the pressurized specimen in a water bath and the escaping gas forms a trail of gas bubbles as it rises to the surface of the liquid

62
Q

Vacuum Leak Testing

A

Uses a vacuum to create the pressure difference necessary for leak detection

63
Q

What is a disadvantage of Vacuum Leak Testing?

A

Because the best possible vacuum is 101 kPa below atmospheric pressure, the pressure differential is limited

64
Q

What is a benefit of the limited pressure differential in Vacuum Leak Testing?

A

The danger of implosion is reduced

65
Q

What is the procedure for Vacuum Leak Testing?

A
  1. The specimen is placed in a vacuum chamber or a vacuum chamber is attached to the side of the vessel
  2. A pump removes air from the chamber, causing the pressure to drop
  3. Because a pressure difference exists between the interior of the vessel or sample and the vacuum chamber, leakage occurs through any cracks or other openings
66
Q

For what applications is Vacuum Leak Testing used?

A
  1. Testing electrical equipment
  2. Laboratory
  3. Floor plates of vertical tanks
67
Q

For what application is Vacuum Leak Testing seldom used?

A

Pressure vessels

68
Q

Dye Tracer Leak Testing

A

Fluorescent dye is added to the water inside a vessel undergoing Hydrostatic Testing to increase the visibility of very small leaks.

69
Q

How does Dye Tracer Leak Testing make leaks more visible?

A

The dye leaks through the cracks or openings to the outside of the vessel and by examining the external surface of the vessel with an UV light, the dye is seen more readily than water

70
Q

Halogen Leak Testing

A

Testing method that uses Freon or halogen gases to fill the vessel and a halogen detector probe to detect leaks

71
Q

Why is Halogen Leak Testing being phased out?

A

The use of halocarbon gases poses environmental problems

72
Q

What is the most sensitive leak detector available?

A

Mass Spectrometers

73
Q

Helium Mass Spectrometer Leak Testing

A

Testing method that introduces a tracer gas such as helium into the test vessel and moves a detector “sniffer” hose over the surface to locate leaks

74
Q

What are the benefits of using Helium as the testing medium for Leak Testing?

A
  1. Because helium atoms are smaller than most other atoms, they penertrate through smaller cracks, provifing a more sensitive test
  2. Helium is an inert gas that does not react with other gases or materials of construction
  3. The amount of helium in the atmosphere is not significant and does not interfere with leak testing

2A2-5: Testing of Metals (12 decks)

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