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MLP Conference 2013. Spark Spectrometry for Determination of Carbon Equivalent. Presented by: Ian Cleary, Acuren. Minneapolis, MN April 24-25, 2013. ABSTRACT.

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mlp conference 2013

MLP Conference 2013

Spark Spectrometry for Determination of Carbon Equivalent

Presented by:

Ian Cleary, Acuren

Minneapolis, MN

April 24-25, 2013

abstract
ABSTRACT
  • As pipeline maintenance and repair activities proceed at a faster and faster pace, the quality control of those repairs must keep pace
  • Laboratory testing of steel chemistry is a major bottleneck in the process of welding to active pipelines
  • Spark optical emission spectroscopy offers a fast and reliable way to get accurate chemistry results in the field
some history
SOME HISTORY
  • Strome, Alberta (February 19, 1985 – 8:00 pm)
  • Workers caught in the unplanned ignition of leaking LNG from a pipeline they were working on
  • Fireball 40m across
cold cracking
COLD CRACKING
  • The leak was caused by cold cracking at a weld in the pipe
  • Typically occurs at the toe of the weld, in the HAZ (Heat Affected Zone)
  • Metal in HAZ cools rapidly after welding, which tends to harden the steel and make it more susceptible to hydrogen induced cold cracking.
cold cracking1
COLD CRACKING
  • How hard the steel will become after welding is related to its chemistry
  • Several elements affect hardenability
  • Most important elements: carbon and carbon-equivalent (manganese, silicon, nickel, chromium)
carbon equivalent ce
CARBON EQUIVALENT (CE)
  • Low carbon = less likely to harden excessively
  • High carbon = more likely to harden excessively
  • Calculating carbon equivalent CE) attempts to estimate how much each element is “worth” in terms of resultant hardenability
carbon equivalent
CARBON EQUIVALENT
  • In early days, pipeline industry had few regulations around steel chemistry.
  • Carbon content guidelines were in place, but other elements were often ignored
  • Steel chemistry results not stored for future generations
carbon equivalent1
CARBON EQUIVALENT
  • Welding on these pipes presents potential for serious hazard, if not handled correctly
  • Regulations now require that carbon equivalent of the existing pipe be known before welding can occur
testing carbon equivalent
TESTING CARBON EQUIVALENT
  • Currently, one way CE can be determined is by testing pipeline shavings in the laboratory.
  • Small amount of metal shavings are collected from a pipe where welding will happen.
testing carbon equivalent2
TESTING CARBON EQUIVALENT
  • Shavings sent back to Acuren laboratory where they are analyzed
  • Problem: Process takes time (transport + testing + backlog)
  • With hundreds of samples coming in from hundreds of locations, chemical analysis is a major bottleneck in the pipeline maintenance process
testing carbon equivalent3
TESTING CARBON EQUIVALENT
  • Acuren intends to introduce a new method for quickly determining carbon equivalent in the field.
portable testing
PORTABLE TESTING
  • A few portable material identification technologies exist, but most have serious limitations.
  • For example: Positive Material Identification (PMI) is unable to detect carbon
portable testing1
PORTABLE TESTING
  • Our solution: Spark Optical Emission Spectrometry (Spark OES)
  • Acuren plans to mobilize spark OES to eliminate the testing bottleneck
spark oes
SPARK OES
  • Each element has a characteristic emission line
  • Spark OES measures chemical composition of metal by igniting a tiny portion of it with a high voltage electric spark
  • Machine detects emission lines with two sensors: a light optic and an ultraviolet (UV) optic.
spark oes1
SPARK OES
  • Wavelengths mapped to characteristic emission lines of each element
  • Machine compares intensity of each emission to a standard, determining the concentration of each element within the sample
site preparation
SITE PREPARATION
  • First step (most important): surface preparation
  • Surface must be clean and flat
  • Spark OES is highly sensitive – any amount of grease, dust, or contamination will cause incorrect results
site preparation1
SITE PREPARATION
  • Acuren’s operators trained in proper surface prep procedures:1) Surface buffed down with grinding wheel2) Grinding wheel replace with fresh one3) Surface polished to ensure no contaminants remain
  • Aluminum oxide or zirconium oxide disks must be used instead of silicon carbide to prevent carbon contamination.
testing
TESTING
  • Head of probe has a detachable adapter that is the working end of the spark machine
  • To take a reading, adapter is held against the surface of the sample
  • Operator presses the trigger
  • Spark is emitted from an electrode within the adapter
testing1
TESTING
  • Spark penetrates a few hundred μm into the surface and ignites the metal
  • Surface must be flat so that plasma is contained within the adapter
testing2
TESTING
  • UV spectrum detected in head of probe
  • Ordinary light spectrum transmitted by fiber optic through probe cable and into main housing of the spark unit
  • Longest fiber optic cable that can be used is eight meters (past that the light signal becomes degraded with loss of results)
  • Intensities of the wavelengths are detected and results analyzed by a proprietary algorithm
analysis calibration
ANALYSIS & CALIBRATION
  • Analysis algorithm relies on an automated calibration procedure: “iCalization” or “iCal”
  • “iCal” works by testing an iCal reference standard – a piece of metal of precisely known composition – at the beginning of a shift, after transportation, or after cleaning
analysis calibration1
ANALYSIS & CALIBRATION
  • iCal builds up a library of readings of this standard material that allows machine to compensate for changes in temperature and humidity, vibrating during transport, and minute differences in component placement after cleaning
  • Adapter thoroughly cleaned after 50 uses
  • Argon gas is used to flush the machine of water vapor and oxygen before each test.
analysis calibration2
ANALYSIS & CALIBRATION
  • To ensure accuracy of readings, a second metal of known composition (the control standard) is tested every time the machine is set up
  • Unlike iCal the control standard was chosen because composition is very similar to the pipeline that will be analyzed
  • Second calibration allows operator to determine if spark testing unit is reading accurately in range of interest
pipeline testing
PIPELINE TESTING
  • Acuren has dedicated three of its four TXC03 spark testing units to carbon equivalent evaluation of pipelines digs.
  • These three machines have been fine tuned to give the most accurate possible results in the expected composition ranges of existing pipes
expected compositions1
EXPECTED COMPOSITIONS
  • Therefore the dedicated spark testing units will yield high accuracy results on any existing line, with special attention to the old pipe.
on site testing
ON SITE TESTING
  • Size and weight of the spark machines is a limitation
    • Each machine has dedicated truck and crew
    • Each unit mounted on hand truck secured to back of crew cab vehicle
    • Deploying unit is two-person job, rolling the truck down a ramp onto the ground with the help of a winch
    • Once on ground, machine can be wheeled to edge of excavation ditch
on site testing1
ON SITE TESTING
  • Eight meter cable often allows main housing of machine to remain outside ditch
  • Once powered up the machine is tested on the control standards to verify proper operation and calibration
  • If test fails the machine is recalibrated with iCal
  • If iCal fails repeatedly, machine is taken back to shop for examination
on site testing2
ON SITE TESTING
  • Each spark test crew consists of an operator and experienced non-destructive examination (NDE) technician who know the client’s procedures and requirements
  • NDE technician performs magnetic particle inspection and ultrasonic testing of proposed test area to ensure polishing is done according to client regulations
on site testing3
ON SITE TESTING
  • Polishing is performed with 120 grit and will go no deeper than 5-8% of nominal wall thickness
  • When appropriate test area is located, operator prepares surfaces and performs test
  • Single spark test consists of at least three readings in same small area
on site testing5
ON SITE TESTING
  • Operator checks burn marks left by machine as well as consistency of readings to determine if burns were good
  • Good = black with small white spot at center
  • Bad = grey or white
environmental variables
ENVIRONMENTAL VARIABLES
  • Optics must have operating temp. of 36°C
    • Unit has built in heating system
    • Extreme cold weather can increase time taken for instrument warming
    • Acuren’s spark testing machines will be contained within insulated boxes with electric heating pads
environmental variables1
ENVIRONMENTAL VARIABLES
  • Primary screen
    • Stops working in extreme cold conditions
    • Machine will need a tent to keep warm and dry while shielding the screen from glare
    • TX03 comes with app for iPad that allows operator to see results in real time without leaving ditch.
conclusions
CONCLUSIONS
  • Spark spectrometry can give fast, accurate results in the field
  • No longer need to send samples back to lab
  • Report is printed in PDF format at site.
conclusions1
CONCLUSIONS
  • Our lab tests show that spark spectrometry can give very consistent readings from one measurement to the next.
  • With proper calibration and surface preparation, spark spectrometers are a portable way to get results:
    • Repeatable
    • Precise
    • Accurate
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