Carbon steels with low-Si (< 0.10 %) content can corrode at an accelerated rate when exposed to sulfidation corrosion conditions. Detecting silicon content in carbon steel via X-ray fluorescence (XRF) and optical emission spectroscopy (OES) has been performed in recent years, though typically during downtime under ambient temperatures. Recent advancements in handheld X-ray Fluorescence (XRF) to quantify levels of silicon (Si) in carbon steel as it pertains to API RP 939-C’s avoiding sulfidation corrosion failures in oil refineries will be discussed. The utility of handheld XRF is explained in practical terms that apply directly to industrial material testing and specifically the surface and environmental variables that affect in situ trace Si testing in high temperatures. Recent developments are identified and their impact as related directly to this application. Dramatically improved hardware and software bring a new level of speed, improved accuracy and precision to the detection of silicon at concentrations below 0.10 wt % in carbon steel process piping systems and components up to 900F. Specifically, better detector/signal processing (1.5X higher count rate, resolution <145 eV) produces improved sensitivity and allows reduced test times in high temperature environments. Additionally the heat sink, standoff and fan design of current instruments mitigate the effects of heat on the instrument.

1. XRF Advancements Improve Detection of Trace Silicon
in Carbon Steel in On-Line, High-Temperature Process
Piping and Components
Olympus | Michael W. Hull, Alex Thurston, Dianne Hillhouse
ASNT | Long Beach, CA | 27 October 2016

2. Advances in low-Si testing
Importance of low-Si testing
Challenges of low-Si testing

3. Importance of low-Si testing

4. Why positive material identification (PMI)?
“Final Investigation Report: Chevron Richmond Refinery Pipe Rupture and Fire” U.S. Chemical Safety and Hazard
Investigation Board. Report No. 2012-03-I-CA. January 2015
“Positive Material Verification: Prevent Errors During Alloy Steel Systems Maintenance” Safety Bulletin, U.S. Chemical
Safety and Hazard Investigation Board. Report No. 2005-04-B. October 2006

5. Why positive material identification (PMI)?

6. Sulfidic corrosion
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Scale formation Internal diffusion

7. Factors affecting sulfidic corrosion
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Temperature
Source: NCSS Statistical Software, https://www.ncss.com/software/ncss/ncss-plots-and-graphs/
SH
S
S
S
SH2
CO2H
S
R
CO2H H2
[ ]n [ ]n
[ ]n [ ]n
[ ]n

8. Alloy effects
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Chromium Silicon
a
l
l
o
y
I
n
g
c
o
n
t
e
n
t
FeCr2S4

9. Corrosion Rate vs Silicon Content
0.0
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8.0
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18.0
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Silicon Content (Weight %)
CorrosionRate(mpy)
Alloy effects
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Source: American Petroleum Institute Recommended Practice 939-C: Guidelines for Avoiding Sulfidation (Sulfidic)
Corrosion Failures in Oil Refineries, 2nd Ed, Annex C

10. 1940 1950 1960 1970 1980 1990 2000 2010 2020
Time • Knowledge • Risk
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1940 1950 1960 1970 1980 1990 2000 2010 2020
Construction
Understanding

11. History and variation in steel specifications
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C
(max)
Si
(min)
P
(max)
S
(min)
Ti
(max)
V
(max)
Cr
(max)
Mn
(max) Fe
Ni
(max)
Cu
(max)
Mo
(max)
A53B 0.30* --- 0.05 0.045 --- 0.08 0.4 1.20* bal. 0.4 0.4 0.15
API 5L 0.28* --- 0.08* 0.03 0.06 --- --- 1.85* bal. --- --- ---
A105 0.35* 0.1 0.035 0.04 --- 0.08 0.3 1.05* bal. 0.4 0.4 0.12
A106 0.35* 0.1 0.035 0.035 --- 0.08 0.4 1.06* bal. 0.4 0.4 0.15
A181 0.35* 0.1 0.05 0.05 --- --- --- 1.10 bal. --- --- ---
A234 0.35* 0.1 0.05 0.058 --- 0.08 0.04 1.06* bal. 0.04 0.04 0.15

12. OLYMPUS Scientific Solutions
API Recommended Practice 939-C
- Guidelines for Avoiding Sulfidic Corrosion Failures in Oil Refineries
§ Result of naturally occurring sulfur compounds found in crude oil.
§ Causes accelerated corrosion in steel fittings, piping, heater tubes, and
pressure vessels when the oil is heated for separation.
§ A significant cause of leaks and failures of piping systems within the refining
industry.
§ Process streams with hydrogen free, sulfurous material may exhibit corrosion in
carbon steel piping with less than 0.1% Si (McConomy Curves)
– Increasing Cr content of the alloy can provide increasing resistance to this
form of corrosion
§ Streams with a combination of hydrogen and sulfur-containing materials at
elevated temperature can corrode steels with Cr levels below 12% (i.e. non-
stainless alloys, Couper-Gorman curves)
– Recommended to use 18Cr-8Ni stainless steel to avoid corrosion

13. Importance of low-Si testing
Challenges of low-Si testing

14. Challenges to trace silicon testing
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Challenging
Environmental
variables
Contaminations Low
concentrations

15. Surface preparation
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Prepare & verify
Coatings, platings Residual paint Corrosion, scale, oxide
layer
Sand-blasting
(Residual Si)
Shot-blasting
(residual from
iron pellets)
Metallic dust

16. Environmental variables
Source: U.S. Energy Information Administration, U.S. Energy Mapping System, http://www.eia.gov/state/maps.cfm
Source: Climate.gov
https://www.climate.gov/maps-data/data-snapshots/averagetemp-monthly-cmb-2015-10-00?theme=Temperature

17. Low concentration
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0
0.1
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0.4
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0.9
1
0 20 40 60 80 100
FluorescenceYield
Atomic Number
Fluorescence yield of elements
K Series
L Series
M Series
Mass attenuation
coefficient (Fe)
Si 2457.94
Cr 110.97
Mn 87.85

18. Low concentration
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High
absorbance
Low
emittance

19. Advances in low-Si testing
Importance of low-Si testing
Challenges of low-Si testing

20. Vanta™ handheld XRF analyzer engineering
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Temperature control

21. Vanta analyzer engineering
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Temperature control

22. Vanta analyzer engineering
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Temperature control

23. 0
10
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60
70
11:30 AM 12:00 PM 12:30 PM 1:00 PM 1:30 PM 2:00 PM 2:30 PM 3:00 PM 3:30 PM
Instrument Temperature
Spot 1 Spot 2
Vanta analyzer engineering
OLYMPUS Scientific Solutions
Temperature control

24. OLYMPUS Scientific Solutions
Vanta analyzer engineering
Temperature control
0
10
20
30
40
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60
70
11:30 AM 12:00 PM 12:30 PM 1:00 PM 1:30 PM 2:00 PM 2:30 PM 3:00 PM 3:30 PM
Instrument Temperature
Spot 1 Spot 2

25. Instrument Stability
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0
5
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25
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6.390
6.395
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6.425
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6.445
6.450
0 100 200 300 400 500 600 700 800 900 1000
Temperature(°C)
Voltage(KeV)
Stability with Temperature Cycling
Manganese Peak Temperature
Less than 0.002 KeV variance

26. Instrument Stability
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0.00
1.00
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0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000
316 SS Measurement with Temperature Cycling
Cr Mn Ni Mo

27. OLYMPUS Scientific Solutions
0
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0 10 20 30 40 50 60
InstrumentTemperature(°C)
Sequential Test Number
Instrument temperature during hot testing
400 F 500 F 600 F

28. OLYMPUS Scientific Solutions
0.00
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0.90
1.00
1.10
1.20
0 5 10 15 20 25 30 35 40 45 50 55 60 65
Concentration(%)
Sequential Test Number
Mn/Mo concentration values during hot testing
Mn 400 F
Mo 400 F
Mn 500 F
Mo 500 F
Mn 600 F
Mo 600 F
400 °F 500 °F 600 °F
Mn Mo Mn Mo Mn Mo
Certified Value 0.86 0.493 0.86 0.493 0.86 0.493
Average (Vanta) 0.88 0.502 0.88 0.504 0.88 0.504
Minimum 0.83 0.486 0.83 0.488 0.83 0.490
Maximum 0.94 0.518 0.92 0.525 0.94 0.527
RSD 6.17% 3.19% 4.95% 3.65% 6.11% 3.72%

29. Window for high temperature testing
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Before After

30. OLYMPUS Scientific Solutions
y = 1.0737x - 0.0123
R² = 0.9949
0.00
0.05
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0.15
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0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
VantaMeasurement
Certified Assay
Si performance on low alloys
Silicon concentration
Alloy grade
CS 1117 CS 1144 CS 1050 CS 1018 CS 4140 C ½ Mo
Assay value 0.05 0.18 0.211 0.252 0.28 0.331
Vanta measurement 0.04 0.18 0.219 0.264 0.27 0.348
Standard deviation 0.008 0.012 0.0140 0.0146 0.018 0.0116
Accuracy
Bias
Precision

31. OLYMPUS Scientific Solutions
0.00
0.03
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0.13
0.15
0.18
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0.23
0.25
0.28
0.30
0.33
0.35
0.38
0.40
0 5 10 15 20 25
Concentration(%)
Sequential Test Number
Repeatability of Si measurements
CS 1018 CS 4140 CS 1144 CS 1050 C 1/2 Mo

32. Future Endeavors
§ Certified samples of lower concentration
§ High temperature calibration for light elements
§ Industrial partners for field testing