In-Place Pipe Support Load Testing and Hanger Surveys_Part of a Best in Class FFS Program
1. In-Place Pipe Support Load Testing & Hanger Surveys
Part of a Best in Class Fitness-For-Service Program
Lange Kimball, Joe Frey, P.E., Britt Bettell
INTRODUCTION
Unless the plant engineer knows what he has, how can
he be assured that his critical piping systems aren’t
imposing potentially damaging loads and stresses on
his equipment if not on the piping itself? Piping Codes
provide guidance for the operation and maintenance of
piping systems and pipe hangers and supports. But is
it enough? This article introduces portions of a “Best-
In-Class” Fitness-for-Service (FFS) program that in-
cludes the performance of regular visual inspections
of pipe supports and hangers, coupled with in-situ load
testing of suspect supports. Such a program will help
give the plant engineer the knowledge he needs to
make sound operational and maintenance decisions.
A best in class FFS program for piping systems has 5
major steps. They include:
(1) Collect and review design, operating, main
tenanceandinspectionhistoryofthepipingsystem;
(2) System walk down in both the hot
and cold condition, and design verification;
(3) As-Found pipe linear elastic stress analysis;
(4) Creep stress analysis; and
(5) Appropriate inspections and testing. With this
information at hand, the plant engineer has veri-
fiable information that will help him maintain his
piping as safely and reliably as possible.
The first two steps described above involve perform-
ing regular pipe support surveys aimed at document-
ing the visual condition of the pipe and supports. If
pipe supports are in distress, it generally means that
the associated piping is in distress. However, not all
pipe supports that appear to be operating normally
are. Spring hangers may be aged or internally fouled
and rigid rod hangers located in critical locations may
not be carrying the design loads. Without this actual
operating data, the analyses may provide erroneous
results. In-situ pipe support load testing allows the
operator to physically determine the load and oper-
ability of the hanger without uncoupling the support
from the pipe. The testing can even be done online.
PIPE SUPPORT MAINTENANCE
ASME B31.1 Power Piping Code provide require-
ments and guidance for the design, fabrication, in-
stallation, operation, and maintenance of piping
systems and pipe supports. The maintenance require-
ments and guidance is provided in B31.1 Mandato-
ry Chapter VII on the Operation and Maintenance of
Covered Pipe Systems (CPS) and B31.1 Non-Man-
datory Appendix V on the Recommended Practice
for Operation, Maintenance and Modification of Oth-
er Piping Systems. ASME B31.3 Process Piping
Code provides requirements for visually inspecting
pipe supports during installation and initial startup in
Chapter VI Inspection, Examination and Testing.
For in-service inspection of pipe hangers, the
American Petroleum Institute (API) has published
API-570 and API-574, aimed at helping identify
pipe support and piping damage mechanisms.
It is up to each facility’s engineering staff to set up
a program to systematically and periodically identify
anything that could jeopardize the safety and reliability
of the plant piping.
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Unless the plant engineer knows
what he has, how can he be assured
that his critical piping systems aren’t
imposingpotentiallydamagingloadsand
stresses on his equipment if not on the
piping itself?
2. WHAT IS A PIPE SUPPORT?
A “Pipe Support” can include anything that:
• Supports a pipe’s deadweight
• Restrains a pipe’s movement due to thermal
expansion, shock load, vibration, etc.
• Protects a pipe from structural interferences
Pipe Supports can range from simple supports, like
wooden rail road ties, to complex engineered products.
TYPES OF PIPE HANGERS
There are two main categories of pipe supports: (1)
deadweight supports and (2) restraining supports.
Deadweight supports include pipe shoes, rod hang-
ers, and spring supports (including any device that
supports a pipe while allowing normal movement). Re-
straining supports include things like anchors, guides,
stops, vibration controls, and shock absorbers.
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Examples of Types of Pipe Supports and Hangers are:
Figure 1. Pipe Shoe from Anvil Catalog PH-2006
Figure 2. Rod Hanger from Anvil Catalog PH-2006
Figure 3. Variable Spring Hanger from Anvil Catalog PH 2006
Figure 4. ELCEN style Constant Support Hanger
Figure 5. Anvil Style Constant Support Hanger
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Figure 6. Lisega style Constant Support Hanger
Figure 8. Shock Absorber - Snubbers
Figure 7. Vibration Control devices from Anvil Catalog PH-2006
Figure 9. Pipe Hanger Isometric
ConstantLoadSpringHangerscomeinavarietyofcon-
figurations, but essentially do the same thing, uplift the
pipe with a constant force.Shock absorbers and snub-
bers are designed to allow the pipe to move normally
(such as by thermal expansion), but lock up when the
pipeacceleratessuddenly(suchasbyadynamicevent).
WHICH PIPING SYSTEMS ARE COVERED
For Power Plants, the B31.1 Code, Chapter VII, re-
quires a maintenance program for piping systems that
are designated as “covered piping systems (CPS). The
“covered” means that these are the systems covered
under the requirement, not that the piping is insulat-
ed. These are defined in B31.1 as 4” and larger main
steam, hot reheat, cold reheat, and boiler feed pip-
ing. It also includes piping systems that operate above
750F or above 1,025 psi. The operating company may
add other piping systems. Additionally, a pipe support
maintenance program is required for piping systems
that operate in the creep regime. This would include the
Main Steam and Hot Reheat piping (critical lines sup-
plying steam to the turbine-generator from the boiler).
The B31.3 Process Piping Code does not specif-
ically require a pipe support program.
PIPE HANGER INSPECTION PROGRAM
Setting up a pipe hanger inspection program should
include:
1. Gathering as much Design, Fabrication, Instal
lation and Inspection information as possible,
2. Using or creating “As Built” Isometric sketches
with hangers located, and
3. Interviewing any plant personnel (or construc
tionpersonnel)inordertoidentifyareasofconcern.
4. REPORTING THE RESULTS
At a minimum, pipe support inspection reports should
include the following:
• Pipe Isometric sketches (to help locate the
hangers),
• Punch Lists of problems found with recommen-
dations, and
• Documenting photographs.
Figure 10. Hanger Punch List
PIPE SUPPORT LOAD TESTING
Suspect spring hangers and rigid rod hangers
should be adjusted only after an analysis of the
load distribution is completed. The problem is that
the actual load on the hanger or uplifted by the
hanger is not known, except for what is given on
the hanger’s nameplate. For older spring hangers
or spring hangers exposed to severe service, the
load can actually change. These changes may be
due to loss of spring performance due to age, dam-
age to the coil, or in the case of constant support
hangers, damage to the internal pivot points. Nor-
mally, in order to load test a hanger, the support
must be de-coupled from the piping and some sort
of load cell inserted. This can be difficult, especially
if the piping is online. It also requires that the local
piping be temporarily supported during the testing.
ROD LOAD MEASUREMENT (RLM) TECHNOLOGY
Rod Load Measurement (RLM) technology (Figure
11) addresses the problem of uncoupling hangers
for load testing by being “in-situ” or in-place tooling.
RLM is based on the use of hydraulic tools to un-
load the lower portion of the hanger rod.
The hydraulic portion of the equipment is installed
on the rod just beneath the spring (Figure 12).
All-thread with appropriate nuts and eyes ex-
tend from the hydraulic cylinders and engage
the load bolt or pin at the pipe clamp. The
cylinders are actuated until liftoff is achieved
at the load pin. At this point, the hanger rod
between the RLM clamp and pipe attachment
is unloaded. All force is being transferred
through the RLM rods and hydraulic cylinders.
The actual load indicates whether the spring is
functioning properly (i.e. internal corrosion or
fractured spring coils would produce significant-
ly higher or lower loads than expected). Re-
tests are as simple as bleeding off the hydraulic
pressure and then testing again. This is useful
if spring adjustments are required as you can
confirm the new setting immediately.
Figure 11. Typical Rod Load Measurement (RML) set up
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5. Figure 11. Detail showing RLM connection to hanger clamp load
bolt.
RLM is an “in-place” or “in-situ” test. That means
that the piping can still be online during the tests.
A big advantage is that the more critical hot load
is measured. Also, because the tools can be bro-
ken down onsite, the testing can be performed
using rope access, further reducing project costs.
CONCLUSION
Pipe hangers are crucial to the safe and reliable
operation of the piping systems. Various Codes
& Standards recognize the importance of this
and, in some instances, require a program that
at least includes systems exposed to creep. The
current industry trend is to utilize more advanced
analysis techniques that address the material
degradation mechanism of creep. Knowing the
actual pipe support loads greatly increases the
accuracy of the creep stress analysis. Creep
stress analysis results can then be used to identi-
fy pipe inspection locations and set re-inspection
intervals.
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