POWER April 2016 - 22

3. Nondestructive testing. The inspectors shown in this photo are looking for trouble
on Grade 91 piping welds using linear phased array ultrasonic testing techniques. Courtesy:
Tetra Engineering Group
steps are addressed in the event a field
anomaly is present (Figure 1). Repairs
and alterations to hangers are not required
to be performed by an " R-stamp "
holder and often are performed by
knowledgeable plant maintenance personnel.
Hanger adjustments are made in
the cold condition while the settings are
confirmed in the hot condition. A record
of activities is to be kept in field reports
and/or in computer software (Figure 2).
Field inspection intervals are to be performed
by a piping engineer every three
years in addition to annual walkdowns
by plant personnel.
Grade 91 and creep evaluations have
become an integral part of power piping
scope. A great deal of industry attention
has been placed on issues related to degraded
and failed Grade 91 piping components
at combined cycle plants (Figure 3).
Special issues arise when Grade 91 steel
components are welded to dissimilar materials,
such as in the case of P91 to P22
or P91 to stainless steel.
Problems also appear when the weld4.
Thermal shock. The failure shown here was found on a plant's desuperheater attemperator
piping. Courtesy: Tetra Engineering Group
ing and heat treatment process is inadequate.
In such cases, the desired
microstructure is not obtained and the
strength and creep-resistant properties
are usually characterized as being significantly
worse than P22. An efficient
inspection plan should detail the procedure
and specific instructions for hardness
testing equipment, technique, data
requirements, and reporting.
FAC inspection plans are designed to
target key locations commonly affected
by flow velocity, temperature, component
shape, water chemistry, fluid quality,
and pipe material. An effective FAC
inspection plan integrates the initial
audit, an assessment of all high-risk
areas, a water chemistry review and
consultation for reducing risk, periodic
inspections for FAC-susceptible piping
and equipment, and repairs of defective/deteriorated
components. The time
interval for these inspections is between
three and five years.
FAC is commonly known to erode carbon
radation mechanisms that affect piping, and
overall framework for managing reliability.
The technical side covers hanger inspections,
Grade 91 and creep evaluations, FAC
inspections, thermal shock/impingement assessments,
and water/steam hammer.
The administrative scope includes management
responsibilities, program plan,
inspections, fitness for service (using API
22
579-1/ASME FFS-1-Fitness-for-Service),
corrective actions, and alterations. This
article focuses on the technical part of
the program.
Hanger inspections evaluate the overall
state of piping hangers. From visual
inspection to recordkeeping, this plan
determines hanger condition during operation
(hot) and offline (cold). Action
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steel components carrying single-phase
water or two-phase water and steam. Normally,
it does not occur in single-phase
steam. The rate of wear is greatest at temperatures
close to 300F, with low pH and
oxygen concentrations. Geometry changes
and other flow perturbations also have a
significant effect.
Thermal shock (Figure 4) and impingement
assessments include piping that
is at risk of dynamic loading, such as
quench cooling. In combined cycle power
POWER | April 2016

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POWER April 2016

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