Windpower 2009 Poster Presentation

1. WIND TURBINE FOUNDATION SYSTEMS SUPPLY CHAIN CHALLENGES AND
MATERIALS SELECTION
Introduction
The highest grade of anchor bolts currently specified in a wind
turbine foundation is made from ASTM A722 steel of 150 ksi
Ultimate Tensile Strength. The ASTM A722 high strength steel
is manufactured by only one steel mill in North America and the
other option from Europe is considerably more expensive. The
single steel mill in North America that provides this material has
only finite capacity. Further adding to this supply problem is the
use of ASTM A722 threaded rods for Ground Anchor systems
and Segmental Bridge construction. Creating additional capacity
takes time and investment – time that the industry may not have
as its growth proceeds at such a rapid pace. There may be
some Engineering reasons for this material to be the sole option
typically specified in a wind turbine foundation design when the
loading requires it. However, there are other materials that can
be used in place of ASTM A722 on most, if not all, projects that
provide all the necessary mechanical properties required. More
must be done to encourage use of alternate materials in wind
turbine foundation designs. The wind energy industry is one of
the more innovative and it should continue this through all areas
of a project so as to avoid any future growth impediments.
As the wind energy industry continues to grow at a geometric
rate in the United States and Canada, supply chain issues are
becoming more prevalent. The recent passage of the three (3)
year Renewable Energy PTC extension will foster continued
rapid installation of wind energy in the United States. As wind
energy becomes an even more vital part of securing America’s
energy future it is important to eliminate obstacles which could
hinder those efforts. As a point of focus, products for securing
wind turbines to their foundations have a limited number of
suppliers in the market. Of these products, typically referred to
as anchor bolts, there is one particular grade (ASTM A722) that
will cause a supply constraint in the wind industry and impede
successful growth if no additional options are considered for
specification into wind projects. The purpose of this presentation
is to address this constraint and provide options to overcome it.
ASTM A722 Wind Industry Usage (Tons)
0
2000
4000
6000
8000
10000
12000
2008 2009 (est) 2010 (est) 2011 (est) 2012 (est)
A722 150ksi A615 Grade 75
Figure 1
Figure 2
1 – 20% Wind Energy by 2030: Increasing Wind Energy's Contribution to U.S. Electricity Supply, prepared by the
U.S. Department of Energy
Imran Khan – Dayton Superior Corporation – Product Manager – 7777 Washington Village Dr, Suite 130, Dayton, OH 45459
imrankhan@daytonsuperior.com – www.daytonsuperior.com
Wind Energy Growth
As you can see by the chart in Figure 1, the growth in wind
energy installations has been at a geometric pace. This rate of
installations is expected to continue its increase due to the three
(3) year extension of the Production Tax Credit (PTC) passed
late last year and an overwhelming need for alternative energy
solutions. The AWEA and other industry groups have set out to
aid in reaching a goal of having 20% of US energy production
using wind power by the year 2030. This ambitious goal
requires an increase in the number of wind installations up to
16,000 MW per year starting in 2018 and carrying through
2030.1
With the current environment and demand for alternative
energy options fostering its growth wind energy has a strong
advantage over other existing and currently more prolific forms
of energy production. An additional source of influence is the
desire for the United States to develop energy production
alternatives to reduce or eliminate the need for purchasing
energy production materials – such as oil – from other nations.
Wind Power Growth Effects on Supply Chain
It would be expected that such sustained growth in wind installations
would also create stresses on the capacity of the supply chain for
components and manufacturing of all materials needed to install a wind
turbine. The anchor bolts are high strength steel threaded rods used with
heavy hex nuts and washers to secure the massive wind turbine towers to
their foundations. There is a limited number of manufacturers of these
anchor bolt products and an even more limited supply of sources for the
raw steel used in manufacturing the anchor bolts. The most specific area
of constriction in the supply chain relates to ASTM A722 150 ksi steel.
This particular steel product is manufactured by a special method whereas
a hot rolled bar of steel is stretched to 80% of its Ultimate Tensile Strength
and then stress relieved to achieve the high strength properties required in
post-tensioned applications such as those in the wind industry. Due to
limitations in the availability of equipment there is only one steel mill in
North America that is capable of producing ASTM A722 steel. Currently
the relative usage of ASTM A722 steel in anchor bolts compared to the
other steels used is approximately 34% or just under 4000 tons for
approximately 1700 out of 4900 total foundations. As the size of the wind
turbine nacelles increases due to the need for larger MW capacity wind
turbines, this further compounds the constraint.
Other Industries’ Effects on Steel Availability
There are other industries that use ASTM A722 and this usage is not expected to
decrease, but rather increase as with the wind industry. Ground anchor
applications are typically governed by the suggested requirements listed in the
Post-Tensioning Institute’s (PTI) Recommendations for Prestressed Rock and Soil
Anchors. Ground anchors used in construction projects are four (4) to seven (7)
times longer than those used to anchor wind projects. There is also a
considerable amount of ASTM A722 used in segmental bridge construction which
is also an application that continues to grow. The growth in these applications is
expected to be further accelerated in the near term due in part to the most recent
infrastructure spending that is part if the economic stimulus package. Additionally
this growth can be expected to continue well beyond any effects created by the
stimulus package due to the significant improvements required in the highway and
bridge sectors in their current deteriorating state. Finally, there are many projects
in the wind industry that require ground anchors to secure foundations due to the
soil conditions of the project installation sites. These ground anchors are the very
same as those referenced in the PTI Recommendations. Growth in the usage of
ground anchors and segmental bridge construction are thus expected to have a
significant impact on the availability of ASTM A722 for use in wind turbine anchor
bolts.
Currently Used Alternate Materials
The most often used substitute for ASTM A722 steel is 4140 Quench and
Tempered (Q&T) steel. This particular steel is not processed per the
requirements of ASTM A722, but rather meets the Yield and Tensile strength
properties call out by the specification. 4140 Q&T has been used as a substitute
for ASTM A722 steel for a number of years mostly in ground anchors of sizes
above 1-1/2” diameter because ASTM A722 is not domestically available in sizes
larger than 1-1/2” diameter. The availability of this material is also limited due to
limitations in the size of heat treat ovens at most steel mills. There is only one
mill in North America that is capable of producing a 4140 Q&T steel bar over 24
feet in length. Currently this steel mill has reached its maximum output capacity
and thus there is a constriction in supply of 4140 Q&T to the ground anchors
market. This affects the wind industry because a large number of foundations
requiring ground anchors utilize sizes above 1-1/2” diameter and, as mentioned,
those sizes are only available to be manufactured using 4140 Q&T.
Need for a Solution
The issues addressed in this presentation are provided to give focus to a
potential supply chain shortcoming that will affect the ability of the wind energy
industry to continue its opportunity to secure America’s energy future. As we
move forward in the growth of wind energy supply we face an often
overlooked portion of the supply chain which provides, literally, the foundation
for the industry’s success and is one of the biggest threats to impeding its
growth. It is imperative that the Engineering and Development community in
the wind industry take a closer look to identify and allow acceptance of
additional suitable steels used to manufacture anchor bolts for securing wind
turbines to their foundations. If this need is not addressed now our success in
reaching the ambitious goals that are needed for our energy independence will
be jeopardized.