Starting from Scratch
As this was to be the first
ever use of HDPE in a safety-related water pipe system at a nuclear
plant in North America, the team at Callaway had to create a
material specification and related procedures from scratch. In the
process, they underwent a change in mindset from focusing on what
was available to specifying what was really needed. Most
importantly, Callaway engineers began to work closely with members
of the HDPE pipe value chain. These players included The Dow
Chemical Co. (Dow) as the HDPE supplier, WL Plastics Corp. as the pipe
manufacturer, and Independent Pipe Products Inc. for the manufacture
of special pipe fittings. The consultant, Frank Schaaf, Jr. of
Sterling Refrigeration Corp., was also instrumental in the work
necessary to gain approvals from the NRC (Figure 3).
Plastic replaces steel. HPDE pipe and joint fittings
were required to be tested to confirm that they met the quality and
safety specifications of ASME Class 3 nuclear service piping
systems. AmerenUE submitted a special Relief Request to the NRC in
2008 demonstrating that HPDE pipe could be used instead of carbon
steel pipe. Courtesy: Dow Chemical Co.
After an evaluation of available options, and based on the service
condition and stringent requirements for HDPE pipe performance, the
Callaway team selected CONTINUUM DGDA-2492 Bimodal Polyethylene Resin
from Dow as the raw material for its new ESW secondary water pipe
system. Given the groundbreaking nature of the application for HDPE
pipe, no American Society of Mechanical Engineers (ASME) code and
standard is available. Callaway needed to obtain approval from the NRC
through a Relief Request. In order to be approved for use by the NRC,
water pipes manufactured from HDPE had to demonstrate that they could
match the quality and safety specifications of ASME Class 3 nuclear
service piping systems. AmerenUE submitted a special Relief Request to
the NRC in 2008 with documentary evidence proving that the specified
HDPE pipe could be used in lieu of carbon steel Class 3 pipe.
The Relief Request asked for NRC approval for using HDPE pipe
based on the specified CONTINUUM DGDA-2492 resin. Callaway engineers
knew that the HDPE pipe would need to meet water pressures of 161
psig at 95F and 45 psig at 176F. CONTINUUM DGDA-2492 has a 2.5-year
pressure listing by the Plastic Pipe Institute, exceeding the
application of a three-month requirement, at 176F.
Initially, the NRC had a concern regarding the effect of increased
stress intensity on the slow crack growth (SCG) resistance of the
proposed 36-inch pipe. This concern was mitigated because CONTINUUM
DGDA-2492 resin has >10,000h PENT, more than 20 times better than
the most stringent ASTM SCG requirement for PE4710 (a higher
performance standard for HDPE pipe); it meets and exceeds the
requirement at the adjusted higher stress intensity. In addition, the
NRC requested that Callaway conduct extensive testing on the joint to
ensure the integrity of the pipeline. As a result, a total of 168
pieces of fusion joint samples were tested using NRC-recommended test
methods. All joints passed the test without a single failure. The
request was officially approved by the NRC on October 31, 2008.
Place the Pipe
AmerenUE anticipated such a result, and its engineering firm,
Sargent & Lundy LLC, together with its primary construction
contractor, Corrigan Mechanical, moved quickly to make the piping
replacement at Callaway.
Installation of the HDPE ESW pipe project was completed by
December 9, 2008. Approximately 1,800 feet of 36-inch HDPE pipe
(with 4-inch wall thickness) was installed underground at the site.
A number of special HDPE joint fittings at 45-degree and 22.5-degree
angles were also successfully fused to the main pipe components.
The new HDPE ESW system was started up on December 10, 2008, and
immediately demonstrated its value. Callaway engineers noted no
vibrations in the HDPE sections of the system, though some steel
pipe sections in the pump house did vibrate due to a static issue.
In addition, due to the lower friction, the new HDPE pipe was found
to allow about 150 gallons more water flow-through per minute than
the previous steel pipe it replaced, even with a smaller inside
According to the team at Callaway, this installation
is a first important step toward HDPE becoming a preferred material
for safety-related water pipe systems at nuclear power stations.
AmerenUE is already planning to replace other buried piping with
HDPE in other systems in 2009.
— Contributed by Jimmy Zhou (firstname.lastname@example.org), a senior
development specialist for the Dow Chemical Co., and Frank Schaaf
(email@example.com), an energy industry consultant for the Sterling