Pmi

T R E N D S
THE MAGAZINE FOR MATERIALS INSPECTION AND TESTING PERSONNEL
JANUARY 2005 — WINTER • VOLUME 8 • NUMBER 1
Portable PMI Instruments
Inspecting Pressure Vessels
Ultrasonic Testing of Welds
Portable PMI Instruments
Inspecting Pressure Vessels
Ultrasonic Testing of Welds
221212.qxd 3/9/05 3:46 PM Page 1
P
ositive material identification (PMI) is a powerful method-
ology for assuring that manufacturing companies operate
with greater profit, more efficiency, and the highest possible
levels of safety. The requirement for PMI of alloy materials in
refinery systems and petrochemical plant operations has grown
dramatically from the late 1970s when it was a rarity, to nearly
100% PMI in today’s risk-based QC environment. The conse-
quences of using the wrong material in a process plant can range
from costly to disastrous, and may involve loss of plant property,
loss of production capacity, and loss of life. Compared to 1990 vin-
tage PMI tools, the latest hand-held, battery-operated, field
portable X-ray fluorescence (FP-XRF) analyzers (Fig. 1) are about
five times smaller, five times faster, and half the price, and are
equivalent to lab-based XRF in terms of performance. A recently
introduced model has all but eliminated routine maintenance
costs as well.
The Need for PMI
As an example of the critical need for PMI, the inadvertent
substitution of a carbon steel elbow in a 5Cr-
1
⁄2Mo alloy steel pip-
ing system resulted in a premature rupture due to hot sulfide cor-
rosion, which led to a major fire at a Louisiana refinery in 1993
(Ref. 1). These types of incidents are more prevalent than gener-
ally assumed and have led to the adoption of FP-XRF for PMI of
incoming plant replacement parts such as pipes, valves, fittings,
pressure vessels, and welding materials. In high-risk services,
100% inspection of materials is generally required. Until recently,
replacement parts could only be tested at ambient or room tem-
perature. Now, however, the capability to test materials at elevat-
ed temperatures up to 1000°F (543°C) is possible. With this new
capability, parts in service can be tested during plant operation.
This form of testing is referred to as retrospective positive mate-
rials identification or RPMI. The key advantage of RPMI is that
incorrect parts can be detected and the correct parts ordered for
replacement during the next plant shutdown. This provides sav-
ings to facility operation by reducing the time required for “turn-
arounds,” and has the potential for saving many months of opera-
tion under potentially catastrophic conditions.
As a result, most every petrochemical process plant in devel-
oped countries has established a mandate to perform PMI. The
PMI cycle extends to such diverse requirements as analysis of
supplier materials of construction (at the supplier’s facility),
incoming materials, in-stock materials, in-process materials at the
operating plant itself, and, finally, to the salvage of used material
for recycling — Fig. 2.
Guidelines for the implementation of a positive material identifica-
tion program have been published by several organizations, including
the Pipe Fabrication Institute (Ref. 2), the American Petroleum Institute
(Ref. 3), and the American Society for Testing and Materials (Ref. 4).
JAMES R. PASMORE ([email protected]) is Vice President, International Sales, and TOM ANDERSON is
Director of Marketing, NITON LLC, Bend, Ore. JONATHAN J. SHEIN is Executive Vice President, Sales and
Marketing, NITON LLC, Billerica, Mass.
Portable Tools Pack Plenty of
Analyzing Power
BY JAMES R. PASMORE, TOM ANDERSON, AND JONATHAN J. SHEIN
Fig. 1 — Modern PMI tools.
Miniaturized field portable X-ray fluorescence analyzers are powerful tools for
positive material identification
221212.qxd 3/9/05 3:46 PM Page 13
Field Portable XRF
Field portable X-ray fluorescence (FP-XRF) is a technique for
quickly determining, often in-situ, that the correct alloy has been
used for the intended application. Over the past decade, PMI test-
ing tools have been miniaturized, field hardened, and improved in
performance to the point where they are now comparable, for
PMI purposes, to taking the laboratory to the field. These tools
can be effectively used to accurately evaluate alloy grades based
on their elemental composition. The technology will assist in
determining whether a given component or part is in accordance
with drawings and specifications, or whether it should be flagged
as “out of spec.” Today, FP-XRF is widely used to identify incor-
rect materials during PMI of incoming fabricated components, as
well as in-service and in-stock materials.
Positive material identification may be performed in the plant
or in the field under a wide range of operating environments,
including ambient temperatures ranging from 20° to 120°F (–7°
to 49°C), rain, dust, magnetic fields, acoustical noise, surface
vibration, and extreme sample surface temperatures, up to
1000°F (543°C) — Fig. 3.
How FP-XRF Works
When the FP-XRF tool is placed on an alloy component and a mea-
surement initiated, the process of analyzing the alloy composition and
determining the alloy grade is accomplished as follows:
The trigger is activated, moving aside an internal radiation
shield — allowing a low-energy beam of X rays to illuminate the
alloy sample surface. Electrons of elements in the alloys are
exposed to the X-ray beam and are temporarily raised to an excit-
ed state. In the process of nearly instantaneous de-
excitation, these atoms emit characteristic fluorescent X rays —
Fig. 4A. Each of the X rays emitted by the alloy sample’s atoms
possess a well-defined energy — a “characteristic X-ray energy”
— that is unique for each element present. The corresponding
intensity of these characteristic X rays is proportional to the con-
centration of a given element in the sample — Fig. 4B. Therefore,
by measuring both the energy and intensity of the characteristic
X-rays from a sample, both the element and its percentage con-
centration can be determined.
XRF Is Both Qualitative and Quantitative
A FP-XRF instrument can provide both qualitative (what ele-
ments are present) and quantitative (percent composition of
these elements) analysis. In the past, FP-XRF analyzers tradition-
ally employed up to three radioisotopes contained in small cap-
sules; these isotopes were used as primary radiation sources for
excitation of a sample.
X-ray Excitation Source Options
Today, the newest FP-XRF analyzers come with two different
source excitation options. The first uses a single isotope for X-ray
excitation and the other uses an electronic tube. The configura-
tion with only one isotope uses a specially packaged
241
Am to
excite the full range of elements that previously required three
isotopes. This single-isotope version simplifies the design,
improves reliability, reduces the measurements required from
three to one, eliminates periodic source replacements due to
short half-life considerations (
241
Am has a 433 year half-life), and
eliminates source decay as an operational consideration since
measurements never slow down in compensation for weakening
source output. Another added advantage is that the source never
needs replacement, which eliminates routine maintenance costs.
The second configuration of FP-XRF analyzers uses a tube-
excited X-ray source. This configuration shares the advantage of
the isotope-excited X-ray source in that only a single measure-
ment is required. It is also usually subject to fewer regulatory
considerations than isotope-based instruments. The only disad-
vantage of the tube-excitation approach is the cost of eventual
replacement of the tube, which has a finite lifetime of service.
The Detector
A semiconductor detector receives the fluoresced X rays and
converts them to electronic signals. This information is then
passed to the electronics and microprocessor, which analyzes and
displays the alloy composition and grade identification data to the
operator — Fig. 5.
The Complete System
The following provides an overview of the operation of the
complete system based on the step-by-step description — Fig. 6.
1. Primary radiation released and directed at sample.
2. Primary X ray causes ejection of electron from atom in sample.
3. Characteristic X-ray energy released as outer shell electron
fills void.
4. X-ray detector in instrument converts characteristic X ray to
electrical pulse.
5. Signal from detector is amplified and sent to microprocessor
for counting and processing.
6. Element intensity data are processed into element composi-
tion data, and resulting values are used to determine alloy grade
from internal grade library.
7. Alloy composition data and grade identification are dis-
played on screen for user.
Fig. 2 — The PMI cycle.
Fig. 3 — An FP-XRF unit with a high-temperature accessory and
wireless PDA display (in a field-hardened case) for in-service test-
ing at 1000°F.
221212.qxd 3/9/05 3:46 PM Page 14
8. Measurement data are stored in instrument memory for
later recall or download to PC.
Typically, analyzers will quantify a suite of elements including
titanium, vanadium, chromium, manganese, iron, cobalt, nickel,
copper, zinc, zirconium, selenium, niobium, molybdenum, palla-
dium, silver, tin, hafnium, tantalum, tungsten, rhenium, bismuth,
and lead.
Alloy Analysis by XRF
Alloys of primary use in refinery and petrochemical opera-
tions are chromium-molybdenum steels, stainless steels, and
some nickel-based alloys such as the Hastelloys™ and Inconels™.
Carbon steels are less resistant to corrosion, but are less costly
and have good utility in low-corrosion operating environments.
Carbon steels are applicable to portable XRF by generic category
only, e.g., 1010, 1020, 1030, etc.; all carbon steel grades will be
classified generically as “C-Steel.” Often, only 20–25 alloy grades
comprise the entire need in a typical refinery or related-type
process plant.
Note that FP-XRF is not universally applicable to all alloys and
all alloying elements. Figure 7 is an example of alloys used in a
typical petrochemical operation. Of the 22 alloys shown in Fig. 7,
20 are possible to positively identify with the FP-XRF analyzer.
Note that the 304 vs. 304L and 316 vs. 316L differ only in carbon
content. These L-grade alloys cannot be separated with any
portable XRF analyzer, and so will be identified simply as either
304 or 316.
Compensation for Detector, Electronic, and
Other Sources of Drift
All XRF analyzers offer software for the analysis of the X-ray
spectrum obtained by the instrument’s detector. Some instru-
ments require an empirical calibration or frequent standardiza-
tion due to detector instabilities, electronic drift, or isotope decay.
Others with more robust programming eliminate these (often-
neglected) chores by automatically compensating for any source
of drift.
Compensation for Alloy Sizes, Shapes, and
Access
Additional software features include the ability to analyze
small, irregular objects such as small-diameter pipes and tubes,
welding rods, small bolts, flanges, and complex shaped valves.
Some analyzers provide optional attachments for analysis of hot
surfaces. Some have a geometry that lends them to testing in
tight spaces (including corner or fillet welds) — Fig. 8.
Fig. 4 — X-ray production. A — Atomic level; B — macro level.
Fig. 6 — Diagram of the complete system operation of a modern
FP-XRF.
Fig. 5 — Diagram of Si PIN detector.
A B
221212.qxd 3/9/05 3:46 PM Page 15
Testing Time
Typical testing times may run from a few seconds to 20 sec-
onds, depending on several factors including the particular ana-
lyzer in use, the excitation source, the alloy sample itself (both
composition and size), and the standard operating procedure
(SOP) in use by the instrument operator. Some providers of PMI
tools provide a generic SOP for PMI at petrochemical operations.
These procedures can be easily adapted to each operation with
generally only minor changes.
The Testing Process
To initiate a test, the operator places the instrument (or instru-
ment probe) on the surface to be analyzed and either pulls a trig-
ger or pushes a button to open a safety shutter. This process also
activates the electronics and the system begins acquiring spectral
data. Results are displayed on an LCD screen, and generally
include both the chemical composition and the common trade
name of the identified alloy grade. This information is stored for
subsequent download to a PC, and includes any additional identify-
ing criteria input by the operator including: sample name, operator
name, lot number, vendor name, etc. The time and date of each test
are also contained in the downloaded information. Some analyzers
can also display and download the full X-ray energy spectra for doc-
umentation purposes — Fig. 9.
XRF Is Nondestructive
X-ray fluorescence analysis is completely nondestructive to
the component being tested, with little or no sample preparation
required. Analyzers come equipped with a preprogrammed alloy
library of the few hundred most commonly used alloy grades for
identification, which may then be modified or supplemented by
the end user.
Modes of Operation
The most advanced instruments provide at least three differ-
ent analysis modes. The alloy mode performs an analysis for a
variable period of time dependent upon the user depressing the
instrument trigger (the longer the test, the greater the precision).
As the instrument receives X rays from the sample, it performs
the necessary calculations, and displays both the percent con-
centrations of alloying elements and the grade ID of the alloy.
A second available mode of operation is the spectral match
mode, sometimes referred to as “fingerprint” mode. In this mode,
the operator first builds a library of alloys in the instrument mem-
ory by collecting (measuring) X-ray spectra of known standards,
and storing each spectral fingerprint into the instrument along with
its grade name. The instrument can then be used to test the
unknown samples against the library of stored fingerprints for
rapid “match” determinations. In this mode, an unknown alloy can
be identified in as little as in two to three seconds, allowing a large
number of parts to be rapidly sorted in a short period of time.
A third mode is a type standardization mode, or as one popu-
lar provider terms it, a “SuperChem” mode. In this mode, the
unknown alloy is first identified then compared to a stored set of
data for the specific grade. Based on the stored intensity data, the
exact chemistry can be determined, including compensation for
light-element content not directly detectable with the FP-XRF.
This mode provides the most accurate and comprehensive results
when particularly rigorous testing is required.
PMI Reduces Cost
Even routine plant operating costs can be reduced by per-
forming “in-service” inspection. This gives needed alloy compo-
sition information necessary to prioritize and schedule replace-
ment prior to temporary plant shutdown, and allows any
required replacement components to be prefabricated.
Turnaround surprises are subsequently reduced. Field portable
XRF is also used to verify material on new construction sites. As
Fig. 7 — Table of typical alloys used in a refinery with compositions and color codes.
Fig. 8 — Example of access to fillet weld.
221212.qxd 3/9/05 3:46 PM Page 16
a result, petrochemical companies
have developed rigorous PMI pro-
grams, and FP-XRF analyzers have
become the PMI tools of choice. If a
potential failure or reduction in perfor-
mance can be predicted early enough,
there are direct savings in plant and
equipment costs as well as avoidance
of harm to personnel. In addition,
there is potentially a much greater sav-
ings through reducing production
losses due to piping and component
failures.
A study conducted by Marsh and
McLennan (property protection and
risk consultants) reported on the dis-
tribution of large property losses. They
were ranked according to the following
categories and percentages (Fig. 10):
It has been noted that based upon
this study, newspaper reports and indus-
try experiences, piping integrity/relia-
bility has been an area where industry is
making huge improvements. Industry
conferences and meetings attest to the
fact that most operators are in the
process of improving their piping
inspection programs (Ref. 5).
Regulatory Impact
The evolving international climate
in regulations and codes, along with
changes in OSHA PSM (Process Safety
Management) citations related to
mechanical piping integrity, are driving
the increased use of FP-XRF for PMI in
the chemical and petrochemical indus-
tries. It can be expected that ever more
detailed monitoring, testing, and
reporting of process conditions will be
further mandated. However, irrespective of government regula-
tions, it seems likely that society will expect safer operations from
refineries with fewer major incidents such as explosions, fires,
and spills.
OSHA has published Compliance Guidelines and
Recommendations for Process Safety Management (nonmandatory)
— 1910.119, Appendix C, for standard criteria for external (alloy)
inspections. This standard covers piping and vessels, and gives
codes and methodologies for internal and external inspections
and an in-service frequency formula derived from specific alloy
corrosion rates. Companies need to develop testing procedures to
ensure that inspections are conducted effectively and that prod-
uct consistency is maintained throughout the manufacturing
process (Ref. 6).
PMI Inspectors and Managers: 21st Century
Skill Set
Along with evolving procedures and more stringent SOPs for
accomplishing PMI, there has been a marked increase in the skill
requirements of inspectors and maintenance personnel. This evo-
lution in PMI skills tends to bring favor to individuals and testing
companies who have learned to leverage technology tools to
solve problems faster, better, and cheaper. The best practitioners
will use the latest PMI technology and information to inspect the
process and to anticipate problem areas. This has placed a pre-
mium on a new set of competencies — the ability to anticipate or
visualize the process impact based on test data gathered. Much
more of the PMI manager’s job will depend on getting the right
alloy testing information at the right time and applying it with
insight into the potential process system impact.
Conclusions
The 21st century will see dramatic changes in risk-based inspec-
tion practices. Price and performance are no longer a concern; the
latest PMI tools are currently half the price of the most popular
models from only several years ago and performance now rivals lab-
based XRF analyzers for PMI use. These latest tools for PMI incor-
porate the critical advantage of field hardening for use in harsh envi-
ronments of heat, cold, rain, dust, and extreme sample surface tem-
peratures up to 1000°F. Convenience and ease of use have been so
thoroughly addressed in some of the cutting edge models that oper-
ators’ productivity and effectiveness are all but assurred. Today’s
PMI tools are smaller, faster, easier, and more affordable than ever
before. Given the cost savings and avoidance of incidents that these
tools provide, there is no reason why every refinery and petro-
chemical plant should not be using this “refined” technology. ❖
References
1. Reynolds, J. T. 1995. Positive materials identification
(PMI). Inspectioneering Journal, Sept./Oct., p. 4.
2. PFI Standard ES-42.
3. API Recommended Practice 578.
4. ASTM Standard E1476-97.
5. Second International Symposium on the Mechanical
Integrity of Process Piping. 1996. Edited by J. R. Sims et al.
Houston, Tex.: MTI Publication No. 48.
6. Shein, J. J., and Kinney, A. Alloy Analysis: Methods and
Implementation. NITON Corp.
Fig. 9 — Test results. A — X-ray energy spectra; B — display readout.
Fig. 10 — Equipment type and percentage of large losses.
B A
Reprinted with permission from Inspection Trends, January 2005.
© INSPECTION TRENDS. All Rights Reserved. On the Web at www.inspectiontrends.com.
221212.qxd 3/9/05 3:46 PM Page 17