which range from microbes, poor water
chemistry control and underinsulation to
flow-accelerated corrosion and cathodic
protection failure in buried piping. This
corrosion can manifest itself as either
systemwide or highly localized issues –
all with varying degrees of detectability.
Another damage mechanism, cyclic thermal stress, can initiate localized fatigue
cracking. An as-built stress analysis of
the piping system can identify areas to
inspect for this.
Identifying the risk potential that
these damage mechanisms hold for a
piping system requires a failure analysis
program and recordkeeping methodology
that feeds and refines the inspection
program. Risk ratings for failure mechanisms can be based on a number of
factors such as consequences of failure,
ease of detectability, rate of progression
or probability of occurrence. These factors can be considered individually or
combined with multiple factors to achieve
a relative risk rating for each affected
piping component.
Once risk factors have been identified and rated, they need to be applied
to individual piping components so an
overall ranking for each component can
be achieved. Routine walkdowns of the
piping system with as-built drawings
will help identify new exceptions such
as unreported, broken or missing hangers and supports, incorrectly specified
piping components or previously unreported hazards. NDEs are then planned
to inspect the highest-risk components.
Results are evaluated, documented and
fed back into component rankings to
continue to refine a system’s fitness for
service (fig. 1).
Inspections alone will not eliminate
or mitigate all potential risks. Components
that have reached their end of life will
need capital investment to maintain
system integrity and safety. For exam-
ple, a pipe elbow that has corroded
past its minimum safe wall thickness
will need replacement instead of addi-
tional inspections. Human error is
another risk factor that cannot be
eliminated by inspections; it is best
handled instead by operational or
managerial procedures. But a proactive
program of boiler and piping inspec-
tions will reduce the risk of forced out-
ages, increase equipment availability,
increase the safety of personnel, help
eliminate service disruptions to cus-
tomers and provide knowledge for
making informed decisions.
Joe Maciejczyk, PE, is an asso-
ciate with Structural Integrity
Associates in the firm’s Annapolis,
Md., office. A registered profes-
sional engineer, Maciejczyk has
more than 25 years of experience
in the design, fabrication, inspection, testing and
operation of boilers, pressure vessels and piping
systems. His experience spans multiple industries
including utility power plants, district heating
and chilled-water facilities, as well as cogenera-
tion and industrial chemical processing facilities.
Maciejczyk holds a bachelor of science degree
in mechanical engineering from Louisiana State
University and a master of business administra-
tion degree from the University of Pittsburgh. He
can be contacted at jmaciejczyk@structint.com.
All Expansion Joints Are Not Created Equal
The potential for expansion joint failure is one of
the risk factors to be considered in planning piping system
inspections. Although expansion joints are designed to
last 12 years or more in service, premature failures occur;
and when they do, a systematic program approach to
replacing them is needed.
Start treating your expansion joints like an engineered
asset versus a commodity. Make sure you have a data
sheet for each joint containing all its design and fabrication information; the Expansion Joint Manufacturer’s
Association (EJMA), which publishes expansion joint
standards, has such data sheets available for your use in
documenting the parameters under which your expansion
joints are operating. Then review each joint failure and
make sure your findings are captured on the data sheet.
Procure replacement joints from an EJMA member,
which will ensure they adhere to industry quality and
engineering requirements. New joint designs are
continually introduced into the marketplace. If you
are looking to adapt a new design, make sure the
supplier of the new joint design can meet or exceed
the data sheet requirements. If there is any doubt,
utilize the services of the vendor and a mechanical
engineer to properly advise you on the purchase.
