Technical Bulletin # P-03
Identifying Potential Pipe
Weakness
Without Cutting Out Pipe
THE PROBLEM:
Following a failure or some operating
condition which indicates potential problems within a given piping system, many
building operators will make the decision to cut out one or more representative
sections of pipe for metallurgical analysis.
Generally, this operation requires
extended planning in order to completely drain and shutdown the system for
sufficient duration to both cut out a sample and replace it with new stock.
Added to the labor cost for steam fitters are general maintenance and material
costs, as well as charges for metallurgical testing. For pipe systems above 12
inches in diameter, removing even the smallest pipe section for testing
requires an extensive effort. And even then, the information derived can only
be assumed relative to that general area. For critical 24 x 7 computer
sensitive operations, a drain down for exploratory purposes is a virtual
impossibility.
THE SOLUTION:
By taking six to nine hundred ultrasonic
wall thickness measurements over a small localized section of pipe, we can
accurately plot the results to form a representative and detailed three
dimensional graph of the pipe interior. Such work can be completed during
regular hours - requiring no shutdown, cutting, or welding.
While the information derived from this
method of nondestructive analysis will not provide the degree of detail gained
from a full metallurgical investigation, it will confirm or refute a potential
problem location, and document its severity. Due to the quick results, lack of
preparation, and low cost of ultrasonic testing, many individual sites can be
tested for far less than the cost of one full metallurgical analysis.
A full metallurgical investigation can
then be scheduled for only those locations which definitely warrant such
work.
This method of pipe analysis is
particularly useful in locating suspected areas of pitting, and erosion
profiles. A typical graph resulting from our intensive ultrasonic measurement
shows not only the condition of the interior pipe surface, but the relative
thickness of each point as well, since it is plotted to scale. Identifying the
cause of the wall loss, however, is unlikely by this procedure.
For illustration, a 3-D graph of a
3” by 4” section of an actual 10 in. Schedule 80 condenser water pipe
is presented below. Shown is an elevated side view of the pipe with detail of
its interior surface profile. The perspective for the viewer is looking through
the inside wall toward the outside of the pipe. Areas of pitting are indicated
by surface indentations and variances in color and shape; showing a clear line
of deterioration through the center portion of the test area.
In this ultrasonic analysis, ECI
confirmed the presence of pitting at this and at other suspect areas. Such
findings led to a recommendation to further test the pipe by full metallurgical
examination in order to determine the precise extent of the pitting and the
possible cause of such a condition.
Multiple wall thickness readings plotted
in three dimensions is essentially the basis of our tank testing program, and
provides similar diagnostic information. In the illustration below, 1,400 wall
thickness readings taken around the entire circumference of a 2,400 gal.
domestic hot water tank reveals a noticeable groove or channel of corrosion
along the entire horizontal center of the tank at and slightly above the water
line.
For this New York City client, our
testing identified a corrosion condition which was previously unknown.
Remaining thickness values at the lowest areas allowed us to estimate 9 years
of remaining service life. Our recommendation to raise the water level 12 in.
above the zone of corrosion in order to greatly extend the life of the tank was
accepted as an easy fix to a silent problem.
A far more detailed explanation of our
testing and reporting procedures for tanks and vessels can be found under the
heading Testing Services -
Tank Testing at the Testing Services menu.
Testing
Services