MLP Conference 2013
Spark Spectrometry
for Determination of
Carbon Equivalent
Presented by:
Ian Cleary,
Acuren
Minneapolis, MN
April 24-25, 2013
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
2
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
3
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.
4
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)
5
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
6
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
7
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
8
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.
9
TESTING CARBON EQUIVALENT
10
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
11
TESTING CARBON EQUIVALENT
• Acuren intends to introduce a new method
for quickly determining carbon equivalent
in the field.
12
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
13
PORTABLE TESTING
• Our solution: Spark
Optical Emission
Spectrometry
(Spark OES)
• Acuren plans to
mobilize spark OES
to eliminate the
testing bottleneck
14
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.
15
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
16
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
17
SITE PREPARATION
• Acuren’s operators trained in proper
surface prep procedures:
1) Surface buffed down with grinding
wheel
2) Grinding wheel replace with fresh one
3) Surface polished to ensure no
contaminants remain
• Aluminum oxide or zirconium oxide disks
must be used instead of silicon carbide to
prevent carbon contamination.
18
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
19
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
20
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
21
proprietary algorithm
TESTING
22
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
23
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.
24
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
25
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
26
PIPELINE TESTING
27
EXPECTED COMPOSITIONS
Overall
C
Mn
Si
Cu
Ni
Cr
Mo
V
Nb
B
Min
0.10
0.60
0.05
0.01
0.01
0.01
0.01
0.005 0.005 0.001
Max
0.30
1.60
0.40
0.40
0.20
0.25
0.25
0.050 0.070 0.001
28
EXPECTED COMPOSITIONS
• Therefore the dedicated spark testing
units will yield high accuracy results on
any existing line, with special attention to
the old pipe.
29
TX03 ACCURACY (IDEAL
CONDITIONS)
C
Conc.
Level
(ppm)
C (air)
Si
Mn
P
S
10
20
10
10
10
20
10
Precision
50
100
10
500
20
20
10
10
20
30
1000
50
50
20
10
50
20
3000
100
100
40
20
5000
120
120
70
60
10000
150
150
120
120
20000
440
440
150
200
300
30
TC03 ACCURACY (IDEAL
CONDITIONS)
Cr
Conc.
Level
(ppm)
Mo
Ni
Cu
Nb
V
W
B
Precision
50
10
3
10
2
4
100
20
10
10
10
20
10
500
20
10
10
20
20
20
50
1000
20
20
10
20
20
20
80
3000
30
20
40
40
30
50
5000
50
50
40
60
60
50
80
10000
70
120
40
100
100
100
180
20000
80
160
250
120
120
200
300
31
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
32
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
33
back to shop for examination
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
34
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
35
ON SITE TESTING
36
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
37
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
38
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.
39
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.
40
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
41
SPARK SPECTROMETRY FOR DETERMINATION OF CARBON
EQUIVALENTS
Presented by Ian Cleary, Acuren
MLP CONFERENCE 2013
42