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Operation of the Ultrasonic instrument is straightforward, however challenges emerge in obtaining answers to the following:Where do we put the probe? Should we scan the area? Use single point? How can we make it repeatable?Could we find an anomaly again if we looked in 6 months? 2 years?Could someone else find the anomaly?
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Ultrasonic Corrosion Surveys
Presented by
Harold Hadley
Inspection Consultant and Contract Chief Inspector for Provident Energy
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Where to Look
Where to look is the first question when planning a UT corrosion survey. You must have an understanding of: The corrosion potential of the location. Corrosion mechanisms. Where the corrosion will occur.
To understand where the corrosion will occur some understanding of the process is required.
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How to look
How is the data collected?Collect as data points?Collected as scan information?Are the data points to be repeated in the
future?
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How is the data reported?Has information already been collected from
this site?Are there previous reports to refer to? Did the previous inspection take into
account the above comments?
How to look
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Consider a Typical Inlet System
Insulation Kit
Insulation Kit
Insulation Kit
Insulation Kit
Insulation Kit
Insulation Kit
To Inlet separator
To test separator
To inlet separator
To test separator
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Typical Inlet System
Insulation Kit
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Ground level
Where would the corrosion be?
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How to Collect the Data
Operation of the Ultrasonic instrument is straightforward, however challenges emerge in obtaining answers to the following:Where do we put the probe? Should we scan the area? Use single point? How can we make it repeatable?Could we find an anomaly again if we looked
in 6 months? 2 years?Could someone else find the anomaly?
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Consider the Data Collection
350
351352
We need reference points.
Insulation Kit
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Base Line Location Elbows
For elbows start at the first weld and follow the direction of the flow taking a data point every 1.5 inches or 4 cm.
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• Start the data collection in the same area (be sure you are measuring on the bottom).
• In the case of high velocity all measurements should be on the outside of the elbow.
What about horizontal elbows?
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Insulation Kit
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2
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350
351352
A Second Look at the Inlet
• For data points that are on the bottom of the line use the same considerations (352).
• Start the data from a reference point and collect data in the direction or flow.
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Base Line Information Elbows
How is Critical Determined?
How is life expectancy calculated?
Where exactly are these points?
Critical : .087
4 .298* 5 .307
Life Expectancy (Years)
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The Next Surveys
Are we comparing the base line data to current data?
Dec May Apr2002 2004 2006
Look at the data calculations.
Total Avg. PeriodLoss Loss Loss(Mils) MPY MPY
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Consider a 2-Phase Separator
• Where would the corrosion be?• Where would damage be?• What type of corrosion or damage can be expected?
GasPSV to Flare or Tank
Mist Pad
Typical Liquid Level
Float Column
Liquid
Inlet Separator (Two Phase)
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Where to Look on a Vertical Vessel
Mist Pad
Liquid
410
415
420
425
430
Typical Liquid Level
Float Column
Inlet Separator (Two Phase)
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Location Explanations
Why did we look at those locations?Because it is the most likely place that corrosion
damage will occur in a vertical vessel.
Top head: Condensation corrosion and under-deposit corrosion.
Shell: Across the mist pad, Interface between the gas and liquid, Liquid phase, There should be at least one band on each segment.
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Location Explanations
Bottom HeadLiquid phase corrosion,Under-deposit corrosion.
Bottom Elbow Stagnant liquid corrosion potential,Flow induced corrosion.
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Tall Columns
Mist Pad
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Consider a 3-Phase Separator
Where would the corrosion be?
Liquid Hydrocarbon
Inlet Deflector
PSV to flare or tank
Mist EliminatorWeir or Baffle
Liquid Off Points
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Water Level
Gas
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Three Phase Locations
There is little difference when choosing locations for inspection on horizontal or vertical vessels.
(Lay vessel on it’s side, remove some hardware, and alter internal configurations).
Mis
t Pad
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Inlet Reciprocal Compressor
To Plant or Process
1st Stage
Compression
1st Stage Scrubber
1st Stage Cooling
2nd Stage Compression
2nd Stage Cooling
3rd Stage Compression
3rd Stage Cooling
4th Stage Compression
4th Stage Cooling
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2nd Stage Scrubber
3rd Stage Scrubber
4th Stage Scrubber
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Inlet Scrubber
Suction Bottles Discharge Bottle
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Compressor Discharge Scrubber
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1921
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Is corrosion the only damage that could occur?Where would the corrosion be?
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The Locations
Look at all the locations and consider the numerous areas where damage can occur. Rotating Equipment introduces damage due
to the Vibration Factor. The corrosion survey on compressors must
include an inspection for cracking.
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The following are examples of interesting failures and damage.
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Pipeline Failure
A line failed at a Y junction. Junction is under a road. Junction had been worked on.Line PSV’s were being tested prior to Start-up.
Pipeline Failure
Line failed at a Y junction under a road during PSV testing prior to start-up.
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Remember the Following Rules
RUST NEVER SLEEPS
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Remember the Following Rules
CORROSION OCCURS IN LOCATIONS THAT ARE THE:
COLDEST
WETTEST
MOST INCONVENIENT
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Remember the Following Rules
Your job
(should you choose to accept it)
is to find that location!
(This is not Mission Impossible).