API 570 Chap 9 Flashcards
Why is Inspection of buried process piping is different from other process piping inspection
because significant external deterioration can be caused by corrosive soil conditions and the inspection can be hindered by the inaccessibility of the affected areas of the piping
What are some Above-grade Visual Surveillance of buried piping?
include a change in the surface contour of the ground, discoloration of the soil, softening of paving asphalt, pool formation, bubbling water puddles, or noticeable odor. Surveying the route of buried piping is one method of identifying problem areas.
Corrosion cells can form on both bare and coated pipe where the bare steel contacts
the soil.
What is Close-interval Potential Survey?
pipe-to-soil (P/S) potential profile of a pipeline over its entire length by measuring potentials at intervals that do not significantly exceed the depth of the pipe
Cons of Close-interval Potential Survey?
may not be a reliable method for corrosion wall loss inspection, since it can only infer wall loss from
CP potential but not directly detect presence of wall loss
When is Pipe Coating Holiday Survey used and detects? (2)
- used to locate coating defects on buried coated pipes
2. used on newly constructed pipe systems to ensure that the coating is intact and holiday-free.
What else can holiday survey be used to evaluate? (3)
- coating serviceability ,
- the coating effectiveness and
- rate of coating deterioration can be determined.
Lower levels of soil resistivity
are relatively more corrosive than higher levels
Measurements of soil resistivity should be performed using the …. and In cases of parallel pipes or in areas of intersecting pipelines should use….
Wenner Four-Pin Method in accordance with ASTM
G57. / Single-Pin Method
What test to use For measuring resistivity of soil samples from auger holes or excavations,
a soil box serves as a convenient means for obtaining accurate results.
The depth of the piping shall be considered in
selecting the method to be used and the location of samples.
Who should keep appropriate records of CP monitoring and maintenance performed as a result of CP system monitoring
Owner/users
buried piping should be located __(where)___ indication (what )
on a drawing (i.e. plot plan or piping iso) indicating size and external corrosion mitigation
What temp repairs should be avoid on buried piping?
bolted clamps
What to be done if the buried pipe is clamped and reburied?
the location of the clamp shall be logged in the inspection record and may be surface marked and the date of installation should be noted.
What to be done if the buried pipe is clamped and reburied?
the location of the clamp shall be logged in the inspection record and may be surface marked and the date of installation should be noted.
some technique for inspection of buried piping? NDE? (2)
long range ultrasonics (LRUT) or guided wave ultrasonic testing (GWUT)
techniques distance?
These technologies may allow 15 ft or longer distances to be screened from one installation and provide a screening assessment of the pipe
frequency of visual?
6 months
frequency/inspection of pipe to soil for poorly coating pipes where CP are inconsistent and for piping with no CP and where leaks have occurred
- poorly coated pipes where cathodic protection potentials are inconsistent, the survey may be conducted at 3-5 intervals for verification of continuous corrosion control.
- For piping with no CP or in areas where leaks have occurred due to external corrosion pipe-to-soil potential survey may be conducted along the pipe route. The pipe should be excavated for inspection or inspected with appropriate NDE at sites where possibilities of active corrosion cells have been located to determine the extent of corrosion damage.
frequency of Pipe Coating Holiday Survey?
usually based on indications that other forms of corrosion control are ineffective. For example, on a coated pipe where there is gradual loss of cathodic protection potentials or an external corrosion leak occurs at a coating defect, a pipe coating holiday survey may be used to evaluate the coating.
frequency of Soil Corrosivity For piping buried in lengths greater than 100 ft (30 m) and not cathodically protected,
evaluations of soil corrosivity should be performed at appropriate intervals based on likelihood of change.
frequency of Internal Inspection Intervals
If internal corrosion of buried piping is expected as a result of inspection on the above-grade portion of the line, inspection intervals and methods for the buried portion should be adjusted accordingly. The inspector should be aware of and consider the possibility of accelerated internal corrosion in deadlegs
other method of Inspection if not CP(2)
- pigging to determine wall thickness
2. excavating based on soil resistivity.
Frequency of Inspection for Buried Piping Without Effective Cathodic Protection, based on soil resistivity (3)
- <2,000 5 years
- 2000 to 10,000 10 years
- > 10,000 15years
if excavating for external what length is recommended? and what circumference?
6 to 8 feet / full circumference
If the piping is contained inside a casing pipe, the condition of the casing should be inspected to determine if water and/or soil has entered the casing. The inspector should verify the following: (4)
a) both ends of the casing extend beyond the soil surface,
b) the ends of the casing are sealed if the casing is not self-draining,
c) the pressure-carrying pipe is properly coated and wrapped, and
d) there is no metallic or electrolytic contact between the casing and the pressure carrying pipe
leaking test intervals? (2)
- is leak testing with liquid at a pressure at least 10 % greater than maximum operating pressure at intervals
- one-half the length of those shown in Table 4 for piping NOT cathodically protected
- at the same intervals as shown in Table 4 for cathodically protected piping.
leak test duration? what to do after 4hours? and at what % of pressure loss is it a concern after 4 hours?
8 hours
Four hours after the initial pressurization of the piping system, the pressure should be noted and, if necessary, the line repressurized to original test pressure and isolated from the pressure source.
If, during the remainder of the test period, the pressure decreases more than 5 %, the piping should be visually inspected externally and/or inspected internally to find the leak and assess the extent of corrosion.
What to do after 4 hours into the 8 hours of leak testing?
the pressure should be noted and, if necessary, the line repressurized to original test pressure and isolated from the pressure source.
What about the remaining 5-8 hours of leak testing?
if the pressure decreases more than 5 %, the piping should be visually inspected externally and/or inspected internally to find the leak and assess the extent of corrosion.
What type of test is recommended to locate leak during leak testing?
Sonic Measurements
What other test can be used aside from leak testing?
- temperature-corrected volumetric
- pressure test methods.
- acoustic emission examination and the addition of a tracer fluid to the pressurized line (such as helium or sulfur hexafloride). If the tracer is added to the service fluid, the owner/user shall confirm suitability for process and product.
