1.0
i
Notice and Disclaimer Concerning Liability
e Propane Education and Research Council (PERC) is a non-profi t 501(c)6 trade
organiz
ation authorized by
the
Propane Education and Research Act of 1996 (PERA),
P
ublic Law 104-284.
PERC was created “to enhance consumer and employee safety
and
training,
to
provide for research and development of clean and effi
cient propane
utiliz
ation equipment,
and
to inform and educate the public about safety and other issues
associated
with the use of propane.”
PERC
is
governed by
a
twenty-one member Board
of
Directors appointed by
the
National Propane Gas Association (NPGA) and the Gas
P
rocessors Association (GPA).
PERC program benefi
ciaries include propane retail
mar
keters,
pr
oducers,
transpor
ters and agricultural cooperatives,
as
well as representatives
of
allied service and supply industries (industry members).
e voluntary guidelines as recommended in this document were
de
veloped by
independent
consultants retained by
P
ERC.
While PERC
administers
the process
of obtaining the information, it does not independently test of verify the accuracy of
the
information or methods used to collect the data that supports the conclusions or
r
ecommendations refl
ected in this document.
P
ERC,
NPGA, GP
A and the industry members disclaim any liability for any personal
injur
y,
pr
operty
damage
,
business
losses or other damages of any nature whatsoever,
whether
special,
indir
ect,
consequential
or compensatory,
dir
ectly or indirectly resulting
for
the publication,
use
,
or
reliance on this document,
or
any information,
apparatus,
method, pr
ocess,
or
similar item disclosed in this document.
is disclaimer of liability
shall
apply even if such loss or damage results,
in
whole or in part,
f
rom any acts or
omissions
of or by
any
negligence on the part of PERC,
NPGA, GP
A or industry
members
or any persons who contributed to the development of the information
contained
in this document.
PERC,
NPGA, GP
A and industry members make no
warranty or guaranty as to the accuracy or completeness of any information published in
this
document.
Users of this document should consult the law of their individual jurisdictions for codes,
standar
ds and legal requirements applicable to them.
is document is not intended nor
should
it be construed to (1) set forth policies or procedures which are the general custom
or
practice in the propane industry;
(2)
to establish the legal standards or care
ow
ed by
pr
opane distributors to their customers;
or
(3) to prevent the user from using diff
er
ent
methods
to implement applicable codes,
standar
ds or legal requirements.
By
disseminating or publishing this document,
P
ERC
is
not undertaking to render any
pr
ofessional or other service to or on behalf of any person or entity.
PERC,
NPGA, GP
A
and
the industry members are not undertaking to perform any duty owed by
any
person
or
entity to any third party.
Anyone reading or using this document should rely
on
his or
her
own judgment or,
as
appropriate,
should
seek the advice of a competent professional
in
determining the exercise of reasonable care
in
any and all circumstances.
1.0
ii
About The Program
Cathodic Protection is a program of training material intended for propane technicians
who
install residential and small commercial underground ASME tanks and piping.
e
pr
ogram provides basic knowledge and requirements for the technician to properly
and
effi
ciently provide cathodic protection for underground steel ASME tanks and piping
f
rom corrosion.
e program is conveniently divided into fi
v
e
sections.
1. An
Introduction covering the basics of corrosion,
the
principles of cathodic
pr
otection,and the methods to achieve
pr
otection.
2. Gal
vanic Protection including anodes,
pr
e-installation procedures,
installation
pr
ocedures,
electr
ical isolation,
testing
equipment,
tank-to-soil
potential tests,
tr
oubleshooting and retrofi
tting
.
3. Impr
essed Current Overview which briefl
y covers installation and maintenance.
4. A
48 question fi
ll-in-the-blank quiz with answer key.
5. A
Skills Evaluation form.
e following training tools are available:
1. An
instructional manual (either on CD or in paper format).
2. A companion DVD to be used as a visual aid.
1.0
iii
Acknowledgements
e Propane Education and Research Council (PERC) gratefully acknowledges the
members
of the Safety & Training Advisory Committee (STAC) who served as Subject
Matter
Experts (SME’s) and reviewers.
Without their help,
the
program could not have
been
produced.
L
yndon Rickards
,
Task Force Chairman,
East
ern Propane Gas,
Inc.
Er
ic Leskinen,
Griffi
th Energy,
Inc.
Jer
ry Lucas,
Heritage Propane Partners
Sam
McTier,
Propane Technologies,
LLC
Ken
Mueller,
N
ationwide Agribusiness
omas
Petru,
Railroad Commission of
Texas
Car
lton Revere,
Rev
ere Gas and Appliance
Jeff
Shaff
er
, Shaff
er’s
Bottled
Gas Corp.
Mike Walters, Amerigas
Ross
Warnell,
Ferrellgas
In addition, PERC acknowledges the following individuals and organizations for
pr
oviding staff
,
equipment, technic
al assistance and management support during
pr
oduction of this program.
Hans
Schmoldt
,
A
node Systems,
Inc., Grand
Junction,
C
O.
J
im Reuscher
,
Count
ry
Gas
Co./Inergy LP
, Cr
ystal Lake and Wasco,
I
L.
T
om Aikens
,
T
rinity Industries,
Inc., Dallas,
TX.
S
tuart Flatow
,
VP
,
S
afety & Training,
P
ERC
, W
ashington DC
iv
1.0
v
CATHODIC PROTECTION
Table of Contents
1.0 Introduction
1.1 Basics of Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 e Principles of Cathodic Protection. . . . . . . . . . . . . . . . . . . . 2
2.0 Galvanic Protection
2.1 Galvanic Protection and Anodes. . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Pre-Installation Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Installation Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Electrical Isolation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5 Testing Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6 Tank-to-Soil Potential Tests . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.7 Troubleshooting and Retrofi tting . . . . . . . . . . . . . . . . . . . . . . 20
2.8 Gas Piping Protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.0 Impressed Current
3.1 An Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Vocabulary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Quiz. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Answer Key . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Skills Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Certifi cate of Training. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
1.3 Methods to Achieve Cathodic Protection . . . . . . . . . . . . . . . . . 3
Introduction
1.0
1.1
1
Cathodic
Protection
-
Introduction
1.1 Basics of Corrosion
Corrosion is an aggressive form of rusting…
and
rust to a steel propane tank and metallic
piping
can be fatal.
Heavy
steel propane tanks and metallic piping
may
seem indestructible.
But
as steel ages,
it
begins to show its age as
r
ust.
S
ome rust is superfi
cial and does not
c
ause serious concern.
How
ever,
if
the steel is
in
a bad environment such as wet ground that
contains
natural or man-made chemicals,
the
r
usting process accelerates.
is is what we
c
all
corr
osion.
O
ver time,
the
corrosion causes structural
pr
oblems,
cr
eating pits or holes in the steel.
L
eft
alone
and ignored,
these
holes may
leak, releasing propane into the ground.
e concern is that the leaking propane can
migrate
into a crawl space or basement of a
building
.
Corr
osion can virtually destroy a
pr
opane tank or piping,
and
leaking propane is
potentiall
y dangerous.
1.2
2
Cathodic
Protection
-
Introduction
1.2 The Principles of Cathodic Protection
To live a long and productive existence,
pr
opane tanks and metallic piping also
need
protection .
. . Cathodic
Protection.
In
general
terms,
Cathodic
Protection can be
used
to protect ASME (American Society
of
Mechanical Engineers) underground steel
pr
opane tanks and piping from corrosion.
is is done by
making
the tank a cathode.
Cathodes
will be discussed further in the
manual.
Corr
osion can be defi
ned as a disease of
steel. Coating
the steel tank like many of the
manufacturers do in the factory is the fi rst line
of
defense against corrosion.
Cathodic protection is the second line of
defense
.
It
will make a steel propane tank and
its
piping immune to the disease of corrosion.
1.3
3
Cathodic
Protection
-
Introduction
1.3 Methods to Achieve Cathodic Protection
Underground propane tanks and metal piping
c
an be cathodically
pr
otected in two ways.
e most common way is with magnesium
anodes.
Another
is with impressed current using
pow
er from the local electric utility company.
Although
the two methods diff
er
greatly,
what
’s important to remember,
is
that
c
athodic protection can extend the life of
an
underground tank by helping to prevent
corr
osion and rust.
Impr
essed current systems
will
be covered later in the manual.
Galvanic Protection
2.0
7
Cathodic
Protection
-
Galvanic Protection
2.1
2.1. Galvanic Protection and Anodes
Galvanic Protection uses anodes. Although
ther
e are dozens of diff
erent types of anodes,
the
three most commonly used in the propane
industr
y include high potential magnesium,
(AZ-63
or H-1) magnesium alloy and zinc.
T
ypical installations use one or more anodes
based
on container manufacturer’s
instr
uctions,
geographic
location,
advice
from cathodic
pr
otection experts,
and
company procedures
and
policies.
High
potential anodes may be used in dry or
sandy
areas where it’s
impor
tant for greater
voltage, and therefore more current. ese
anodes
produce a minimum of minus 1.75
v
olts,
v
ersus 1.5 volts for standard anodes.
Z
inc anodes can be used to protect
undergr
ound propane tanks and piping in
coastal
areas where groundwater may be
brac
kish or salty.
8
Cathodic
Protection
-
Galvanic Protection
However, standard minus 1.5 volt magnesium
anodes
are more generally
used
in the propane
industr
y because they work
best
in the
major
ity of underground conditions found in
the
United States.
e purpose of the magnesium anode is to
pr
otect the tank and connected steel piping by
pr
oviding current and electrons to the entire
sur
face area of both.
In
doing this,
the
anode acts like a light bulb,
lighting
up the surface of the steel tank.
is happens because electrons fl
ow from the
external magnesium anode along a wire to the
steel
tank…the cathode.
At
the same time,
a
small
electric current measured in milliamps
fl
ows through the earth from the magnesium
anode
to the steel cathode.
By
using natural
laws
and processes where electric current fl
ows
f
rom a high voltage source to a lower voltage
r
eceiver,
man-made
anodes of higher voltage
metal
such as magnesium will artifi
ciall
y
pr
event lower voltage metal like steel from
decomposing. e electrons actually prevent
the
iron atoms in the steel from oxidizing into
r
ust.
And
if enough electrons fl
ow from an
anode
to the tank,
it
will not corrode,
bec
ause
the
voltage of the tank will change.
2.1
9
Cathodic
Protection
-
Galvanic Protection
is voltage can be measured with a voltmeter
and
a copper sulfate electrode.
Although
diff
erent metals have diff
er
ent
v
oltage readings,
the
voltage reading of steel is
naturall
y
ar
ound minus 0.50 volts.
A
voltage of minus 0.50 volts on a propane
tank
would indicate that the tank is
unpr
otected and is susceptible to corrosion.
2.1
10
Cathodic
Protection
-
Galvanic Protection
To avoid corrosion, the electrons must shift
the
voltage of the steel to a minimum of minus
0.85
volts or more.
e rule is the higher the
v
oltage,
the
better.
How
ever,
the
electrons
should
not shift the voltage above a minus
2.00
volts.
W
hen a tank is totally protected from
corr
osion,
it
means that the entire tank
has
become a cathode.
e length of the
pr
otection measured in years is dependent
on
the severity
of
the environment in which
the tank is installed. If the tank is installed
in
non-corrosive dry sandy soil,
it
may be
r
elatively free of corrosion and the anode will
last
a lifetime.
How
ever,
if
the tank is installed
in
wet,
fer
tilized and sticky clay like under a
lawn
or fl
owerbed,
the
anode could possibly be
consumed
in less time.
2.1
11
Cathodic
Protection
-
Galvanic Protection
2.2 Pre-Installation Preparation
But remember, before you do any digging, fi rst
r
efer to your company’s policy,
or
call the national
hotline
(811) or your local one-call system to
pr
event damage to underground structures.
Although
there are several locations where an
anode
can be placed,
one
way is to dig a hole
so
that the anode can be placed below the
bedding
of the tank.
If
two anodes are being
used, y
ou’ll dig two holes.
Another
way is to place the anode beside the tank.
Again, if
two anodes are being used,
one
can be
placed
on each side or each end of the tank.
W
hen installing two anodes,
they
can also be
placed
diagonally
f
rom each other at the ends
of the tank.
2.2
12
Cathodic
Protection
-
Galvanic Protection
2.3 Installation Procedures
e fi rst thing is to remove the outer box or
plastic
bag from the anode.
e anode should
be
wetted.
One
good way to wet the anode is
to
place it in a bucket brought to the jobsite
and
then fi
ll the bucket with water.
e
idea
is
to let the anode soak up the water.
It
will
do
this because the anode is packaged in a
bag
of gypsum,
sodium
sulfate and bentonite
c
lay.
After a couple of minutes,
turn
the anode
upside
down in the bucket so it soaks up the
remaining water. Another way to wet the anode
is
to pour water over it from the container.
Just
make
sure you get it good and wet and that the
water
soaks in.
is procedure ensures moisture
r
etention and good soil contact.
at way the
anode
will work
mor
e evenly.
Once
the anode is placed in the hole,
unwind
the
wire and temporarily anchor it to the top
of
the hole with a dirt clog or rock.
en
cover
the
anode with dirt from the hole.
2.3
13
Cathodic
Protection
-
Galvanic Protection
Run the anode wire to the connecting lug or
tank
lead wire and make the connection with a
silicon
fi
lled underground wire connector.
is
is
where the manufacturers have made the job
easier
.
ere are no more
ermite welds that
former
ly
needed
to be performed.
e integrity of the tank coating is one factor
in
the success of the Cathodic Protection
sy
stem Once the tank has been set,
make
sure
y
ou’ve touched up any damaged areas on the
tank
that happened while loading,
in
transit,
or unloading at the job site. Tank fabricators
and
coating manufacturers supply touch-up
kits
that are easy to use.
U
se a piece of coarse
sandpaper
to rough up the area around the
ding
.
Wipe the area clean with a dry cloth
and
then apply the coating per manufacturer’s
instr
uctions.
Doing
this puts less of a drain on
the
anode.
In
desert or semi-dry parts of the country,
and
after the tank has been set,
anodes
should
stay
wet so that you get acceptable results on
the tank-to-soil test. One way to do this is to
place
a two inch diameter,
fi
ve foot long plastic
pipe
,
or
any kind of fl
exible tubing into the
hole
next to the anode.
Keep
it upright while
the
hole is being partially backfi
lled.
After
the
tank has been buried,
the
top of the pipe
should
extend a few inches above
the
ground.
In
order to keep what ground moisture there is
f
rom evaporating through the pipe,
place
a cap
on
the pipe.
2.3
14
Cathodic
Protection
-
Galvanic Protection
Once the installation is complete, you’ll want
to
document it for future reference.
Follow
y
our company’s policy and local codes,
but
r
emember,
in
snowy climates,
NFP
A 58
r
equires the tank location to be marked.
2.3
15
Cathodic
Protection
-
Galvanic Protection
2.4
2.4 Electrical Isolation
When metal pipe like steel or copper is used,
electr
ical isolation becomes critical.
All
metals
hav
e a unique voltage stored within them.
Bar
e copper lines must be isolated from the
tank
at the outlet of the regulator on the tank
to
prevent anodes from having to supply more
electr
ical current than necessary to protect
the
tank.
Car
e must be taken to isolate bare
copper
lines from metallic tank domes or the
steel
of the tank.
Blac
k
ir
on or steel lines may be protected
using
the same anode that protects the tank,
but
must be isolated from the building being
ser
ved to prevent the anode from supplying
electrical current to protect everything that’s
undergr
ound at the building that is not a
pr
opane pipe.
16
Cathodic
Protection
-
Galvanic Protection
A dielectric union may provide the necessary
isolation.
Without a dielectric union to isolate
the
tank from bare pipe,
or
insulation to
pr
event a bare copper tubing from touching
the
tank through a metal dome,
the
current
c
an collect on interconnected underground
copper
and steel pipe that connects a
customer
’s well casing or the city water system
and
the electrical grid.
is unwanted loss of
curr
ent is like having the cathodic protection
“light” illuminate all the unwanted previously
mentioned
structures.
2.4
17
Cathodic
Protection
-
Galvanic Protection
2.5 Testing Equipment
Checking your cathodic protection system is
vitall
y
impor
tant.
It
’s
easy
and takes just a few
moments.
All
you need is a voltmeter and a copper
sulfate
electrode to measure the voltage or
stor
ed energy surrounding the tank and its
piping
.
2.5
18
Cathodic
Protection
-
Galvanic Protection
2.6 Tank-to-Soil Potential Tests
First, if the ground is dry where you’re going
to
take the readings,
moisten
it with water.
Also
,
make
sure the electrode has been
pr
operly
maintained
per the manufacturer’s
instr
uctions.
N
ext,
set
the voltmeter on the 2 volt DC
or
the
20 volt DC scale.
en connect the voltmeter to the tank,
with
the
positive lead connected to the multivalve©,
and
the negative lead to the copper electrode.
Do
this at the multivalve© rather than the
dome. While many newer domes are made
f
rom a poly/plastic type of material,
e
ven
if
the dome is metal,
it
might be loose and
y
ou probably won’t get a good reading.
e
m
ultivalve© is well connected to the tank,
and
r
egardless of whether there is brass,
steel
or any
other
metal on the valve,
the
important thing is
that
it is a metal to metal connection between
the
voltmeter and the tank.
2.6
19
Cathodic
Protection
-
Galvanic Protection
en take a couple of steps to the side of the tank
opposite
the dome.
You’ll want to be just above
wher
e the side of the tank is underground.
S
tick
the
tip of the electrode into the ground where you
hav
e moistened it,
and
take your reading.
Recor
d
y
our data according to company policy.
Repeat
the
process on the opposite side of the dome,
and
then
at both ends of the tank.
It
is important to
take
four tank-to-soil potential readings around a
tank
to get a complete picture of the cathodic
protection level. It is possible to record a good
r
eading above
-0.85
volts on one end or one side
of
a tank and have a bad reading below -0.85
v
olts on the opposite end or opposite side of a
tank.
When this happens,
the
areas of the tank
that
have readings above -0.85 volts are protected
while
an area with a reading below -0.85 volts is
not
protected and could still suff
er
corrosion
damage
.
A single reading would not detect an
ar
ea of low protection .
And
remember,
y
ou’ll
want to record all four readings. is information
c
an be valuable for future reference.
e voltage reading on a healthy tank should
be
equal to or greater than minus .85 volts.
e
v
oltage of an anode should be at least minus
1.5
volts.
e voltage of an unprotected tank is
usuall
y
ar
ound minus .50 volts.
When the anode
is
connected to the tank,
the
two voltages average
some
where in between.
If
the average voltage is
high
or close to the voltage of magnesium,
-1.50
v
olts or higher,
this
indicates the tank’s coating is
good. If
the voltage is low or close to the voltage
of steel, there may be any variety of problems
with
the tank or installation.
P
erhaps the
ano
de
was
not connected to
the
tank properly
. If
the copper
anode
wire does not make good strong metal-to-
metal
contact with the tank,
the
reading could
be
low.
Another
possibility for a low reading is
that
the
elect
rode was not making good
cont
act with
the
earth
. A
dditional reasons might be the
r
ubber
b
oot was not removed from the electrode.
e
batt
ery
in
the voltmeter was dead.
e electrode and the
connection to the tank were not good. Or, the anode
has
been consumed and needs to be replaced.
2.6
20
Cathodic Protection - Galvanic Protection
2.7 Troubleshooting and Retrofi tting
When a reading at an existing installation is
zero, you’ll have to do some troubleshooting.
e following is a laundry list of things to
check when troubleshooting.
1. Start with the voltmeter. Is it on?
2. Is the battery good?
3. Have you taken off the rubber boot on the
copper sulfate electrode?
4. Have you set the voltmeter switch to the
d.c. volt scale?
5. Have you connected one lead wire to the
copper sulfate electrode?
6. Have you connected the other lead wire to
the multivalve© securely?
7. Does your copper sulfate electrode have a
blue liquid in it?
8. Have you set the electrode fi rmly on the
ground?
9. Have you poured a glass of water on the
ground if the ground is dry?
10. Are your lead wires and their connections
good?
Bad
Readings
Good
Readings
-1.80
-1.70
-0.80 -1.60
-0.70 -1.50
-0.60 -1.40
-0.50 -1.30
-0.40 -1.20
-0.30 -1.10
-0.20 -1.00
-0.10 -0.90
-0.0 -0.85
2.7
21
Cathodic Protection - Galvanic Protection
If everything you’ve checked is okay, and
the meter reading is below -0.85 volts, the
following is a second checklist. But remember,
not all of these items are going to be off mark
at the same time.
1. In the dome, is there copper tubing leading
from the regulator?
2. Is there a dielectric or insulating union
between the copper tubing and the tank?
3. Is the coating on the tank peeling off or
non-existent in the dome?
4. Is there a steel service pipe and no
dielectric union in the piping at the
building?
5. Is there electrical continuity between the
multivalve
©
and the pipe into the building?
Check this using the ohms resistance
setting and a jumper wire between the
multivalve
©
and the pipe at the building. A
reading less than 20 ohms indicates there
is continuity between the tank and the
building.
6. e anode wire may not be securely
connected to the tank.
7. e anode may have been buried still
inside its plastic bag.
8. e anode may be dry.
9. e anode may be old and have been
consumed.
10. e anode may have been too small (1 lb, 3
lb, 5 lb. anodes are too small).
11. e anode may be lying up against the
opposite side of the tank.
12. Is there a plastic liner under decorative ro
2.7
If everything you’ve checked is okay, and the meter reading is below -0.85 volts, the
following is a second checklist. But remember, not all of these items are going to be off
mark at the same time.
1. In the dome, is there copper tubing leading from the regulator?
2. Is there a dielectric or insulating union between the copper tubing and the tank?
3. Is the coating on the tank peeling off or non-existent in the dome?
4. Is there a steel service pipe and no dielectric union in the piping at the building?
5. Is there electrical continuity between the multivalve
©
and the pipe into the building?
Check this using the ohms resistance setting and a jumper wire between the multivalve
©
and the pipe at the building. A reading less than 20 ohms indicates there is continuity
between the tank and the building.
6. e anode wire may not be securely connected to the tank.
7. e anode may have been buried still inside its plastic bag.
8. e anode may be dry.
9. e anode may be old and have been consumed.
10. e anode may have been too small (1 lb, 3 lb, 5 lb. anodes are too small).
11. e anode may be lying up against the opposite side of the tank.
12. Is there a plastic liner under decorative rock or bark between the electrode and the
tank? If so, punch a small hole with a pencil and pour water at the hole before taking
the reading again.
13. Are you connected to a metal dome and not the multivalve
©
?
22
Cathodic
Protection
-
Galvanic Protection
If everything checks out that you can see, the
gr
ound is moist and your readings are still
below
-0.85 volts,
tr
y this.
T
ake an anode out of its protective plastic bag
or
box,
lay
it on the ground next to the tank,
pour
water on the anode and let the water fl
ow
onto
the ground.
U
sing a 12”
jumper
wire with alligator clips on
each
end,
connect
one end to the multivalve©
and
the other end to an anode wire.
e
v
oltage readings on the tank should start
to
increase in the direction of -0.85 volts.
If the voltage readings do not change, you
could
disconnect a copper service line at the
fi
rst stage regulator inside the dome.
If
the
tank-to-soil
voltage readings immediately
jump
above
-0.85
volts,
y
ou need to install a
dielectr
ic union inside the dome.
If
the voltage
slowl
y increases,
y
ou can now think about
r
etrofi
tting the tank by
adding
a new anode.
If
you need to retrofi
t an existing tank,
befor
e
y
ou do any digging,
r
efer to your company’s
polic
y,
or
call the national hotline (811) or
y
our local one-call system to prevent damage
to underground structures.
2.7
23
Cathodic
Protection
-
Galvanic Protection
First, verify there are no sprinkler lines, low
v
oltage electric wires,
the
propane service line
or
other owner installed bulbs or wires where
y
ou plan to dig.
Cut
out a plug of grass fi
ve
feet
to the side of
the
dome with the shovel and set it aside.
Dig
a vertical hole at least 3 ft.
deep
.
If
this
isn
’t
possible
,
y
ou may have to lay the anode
down
horizontally.
In
dry environments,
the
anode
may work
better
if it is laid horizontally
in
a ditch 18 in.
deep
where sprinkler or rain
water
will wet the anode.
As
stated earlier,
if
the tank is in a desert environment, set a PVC
pipe
in the hole with the anode so that water
c
an be poured into the pipe to wet the anode.
2.7
24
Cathodic
Protection
-
Galvanic Protection
Place the anode in the hole and pour water on it.
T
ouch the anode wire to the multivalve©
while
taking a tank potential reading.
e
r
eading should be above -0.85 volts.
If
so,
continue
with the installation.
If
the reading is
still
not good,
r
efer to the troubleshooting list
on
page 21.
W
ith the shovel,
w
edge the grass apart from
the
anode to the dome,
and
push the wire
down
below the grass into the dirt.
2.7
25
Cathodic
Protection
-
Galvanic Protection
With a portable electric drill, drill a hole
thr
ough the dome…
…and
insert a rubber grommet in the hole.
en,
push
the wire through the hole into the
dome
.
Connect
the wire to the tank at the stud
under
the multivalve©,
or
to the riser pipe
using
a band clamp.
Any
water proofed secure
connection
between the anode wire and the
r
iser pipe or multivalve© will cause the tank
potential
readings to shift to the protected
level of -0.85 volts or greater.
2.7
26
Cathodic
Protection
-
Galvanic Protection
Fill the anode hole with the dirt removed
dur
ing digging and use the shovel handle to
tamp
the dirt around and on top of the anode.
is
fi
lls in the voids between the anode and
the
hole you dug.
If
you don’t do this,
ther
e
will
be a gap between the anode and the hole
that
the current can not fl
ow
across.
is
will
r
educe the amount of current your anode
cr
eates,
and
cause the readings to be lower
than
what is possible.
Replace
the plug of
grass on top of the anode hole and push the
separated
grass back together where the anode
wir
e was run.
Once
you’ve completed these steps,
one
last
major
thing to do is to take a tank to soil
potential
test.
is was covered on pages
18-19
of the manual.
Remember though to
take
four readings,
one
on each side of the
tank
and one on each end,
with
a healthy
r
eading being any voltage equal to or greater
than
minus .85 volts.
But in the unlikely
e
vent that one anode does not increase the
readings to a protected level of -0.85 volts or
gr
eater all around the tank,
install
a second
anode
on the opposite side of the tank.
And…just
like the original installation,
once
done
,
y
ou’ll want to document your work
for
future reference.
Follow your company’s
polic
y and local codes.
If
after following all these procedures and
y
our reading still does not increase to -0.85
volts or greater, it is possible the container is
too
corroded and may need to be removed
f
rom service.
Check with your supervisor for
company
policy regarding these guidelines.
2.7
27
Cathodic
Protection
-
Galvanic Protection
2.8 Gas Piping Protection
e following are general recommendations
for
protecting lines connecting underground
t
anks to buildings or gas utilization equipment
such
as generators.
ese recommendations are
based
on commonly accepted
instal
lation codes
and
good operating practice.
Any deviations
should
be with the recommendation of a
corr
osion specialist and approval of the
author
ity having jurisdiction.
Coated
Steel or Black
I
ron Pipe
–
e
anodes
installed
to protect the tank will also protect
coated
steel or black
ir
on gas lines where a
dielectric union is installed at the building or
gas
utilization equipment.
Coated Copper Tubing – e anodes installed
to
protect the tank will also protect coated
copper
gas lines where a dielectric union is
installed
at the building or gas utilization
equipment.
Uncoated
Steel or Black
I
ron Pipe
-
Uncoated
steel or black
ir
on piping is not
r
ecommended.
NFP
A 58 and good installation
practices
requires black
ir
on or steel pipe to be
coated.
Uncoated
Copper Tubing
-
Because
uncoated
copper tubing does not present
corr
osion problems in most soils that can
r
esult in reduced anode performance and
life, this material must be isolated from
the
underground tank being cathodically
pr
otected.
Use of uncoated copper tubing
is
dependent on local soil conditions and
appr
oval of the authority having jurisdiction.
2.8
28
Cathodic
Protection
-
Galvanic Protection
Coated Steel or Black Iron Pipe With
Uncoated
Fittings
-
Uncoated fi
ttings
should
never be used with coated black
ir
on or
steel
piping.
All
pipe fi
ttings must be coated
and
wrapped before burial.
S
ince coatings,
pipe
sizes,
composition
and
lengths
vary from one job to another,
the
-0.85
volt criterion will determine whether
one
anode or multiple anodes are needed to
achie
ve protection.
Multiple
readings over and
along
a pipe may be needed to confi
rm
that
a
single anode is protecting the gas line from
the tank to the building.
2.8
Impressed Current Overview
3.0
31
Cathodic
Protection
-
Impressed Current Overview
3.1 Impressed Current . . . An Overview
Earlier in the manual, we said there were two
way
s
to
protect underground steel tanks and
metal
piping from corrosion,
with
the most
common
being galvanic protection using
magnesium
anodes.
e second way is with impressed current.
But
ther
e’s a major diff
erence in how the two work
and
where you use one versus the other.
W
hereas galvanic protection works well with
small
tanks usually
meant
for residential and
small
commercial applications,
impr
essed
curr
ent is meant for large bulk storage tanks.
And
know that a company specializing in
cathodic protection should design systems for
installations
larger than 4,000 gallons.
3.1
32
Cathodic
Protection
-
Impressed Current Overview
Earlier, we discussed the current from an
anode
as light from a light bulb.
Curr
ent from an impressed current anode
is
similar to light from a bank of stadium
lights.
erefore,
one
or two impressed
curr
ent anodes is enough to bathe in light
. . . or
protect the entire surface of any size
commer
cial tank .
. . its
liquid lines,
vapor
lines
and
anything else nearby.
How
does this work?
e impressed current
anode
gets its power from a rectifi
er which is
like
a transformer and is as small as a shoebox.
is rectifi er turns a.c. voltage into d.c. voltage
like
a battery charger.
3.1
33
Cathodic
Protection
-
Impressed Current Overview
Whereas a magnesium anode has the power
of
a 1 volt battery,
a
rectifi
er and its anode or
anodes
have the voltage of a car battery and
mor
e! With more voltage,
y
ou get more current,
or
as in our example here .
. . mor
e light.
If
there is resistance in the ground,
that
r
esistance will block the current from an
anode
like smoke blocks light.
But
the impressed current rectifi
er has the
pow
er to force the current through the resistant
ear
th like a searchlight through smoke.
3.1
34
Cathodic
Protection
-
Impressed Current Overview
Although we simplifi ed it, what we’ve just
discussed
are a few of the major diff
er
ences
betw
een galvanic protection and impressed
curr
ent protection.
Of
course there are a lot of
other
diff
er
ences.
Impr
essed current anodes are made of a special
allo
y of cast iron,
silicon
and chromium.
Unlike
magnesium
anodes which are covered with
dir
t from the hole that was dug,
impr
essed
curr
ent anodes are fi
rst encased in coke breeze
bac
kfi
ll,
a
good electrical conductor,
and
then
cov
ered with dirt from the excavation.
Also
,
if
the coating on the tank disintegrates as it gets
old, the
additional current from the impressed
curr
ent anode can compensate for the lack of
coating
.
F
inally,
as
alluded to earlier,
if
there are
electr
ically
gr
ounded structures to the tank,
or
a
long run of underground steel liquid or vapor
lines, the
rectifi
er system can also protect them
for
many years.
3.1
35
Cathodic
Protection
-
Impressed Current Overview
Installation
When it comes to installation, know that
high
voltage is very
danger
ous! Impressed
curr
ent can also,
on
occasion,
harm
unrelated
bur
ied structures around a commercial tank
sy
stem.
Impr
essed current systems need to be
designed
and installed by
people
trained in
the
science of cathodic protection .
. . people
who
are qualifi
ed and know exactly what they
ar
e doing.
Talk with your supervisor before
attempting
to work with impressed current.
3.2
36
Cathodic
Protection
-
Impressed Current Overview
3.3
Maintenance
An impressed current system requires
maintenance
to be certain it is on,
and
that
r
equired current is always
fl
owing to the
anodes.
Rectifi
ers have amp meters that show how
m
uch current is fl
owing to the anodes.
As
long
as
there is an amp meter in the rectifi
er
that
shows
some amperage fl
owing into the anodes,
the
system is on.
A
person should write the
amperage
output down,
date
it and initial the
r
eading for future reference.
If
there is ever any doubt that the rectifi
er
is
on, you should check the output voltage with
a
voltmeter across the + and - terminals of the
r
ectifi
er,
just
as you would across the “+”
and
“-” terminals
of a car battery.
Bec
ause this manual has been designed around
c
athodic protection for residential systems,
w
e
just
wanted to give you a brief overview
of
impressed current.
F
or further information
and
training,
talk
with your supervisor and
see
what your company off
ers.
Just
remember,
impr
essed current systems must be inspected
and maintained by persons or companies
specializing
in cathodic protection systems.
Vocabulary List
39
Cathodic
Protection
-
Vocabulary List
Vocabulary List
A
Anode
Metal
that is oxidized and consumed as it corrodes while giving up its electrons to a
c
athode.
In
usage,
a
bar,
r
od or ingot of magnesium or zinc connected to a steel tank or pipe to
pr
ovide protection from corrosion.
Anodes produce an electrical current and in doing so
graduall
y waste away (see Sacrifi
cial
Anode).
-
Standard (H-1) magnesium anodes are used in average to corrosive soils.
-
High purity magnesium anodes are used in dry,
sandy
soils.
-
Zinc anodes are used where groundwater is salty or brackish.
Impr
essed current (rectifi
er) systems work
b
y
using
current from the electric utility and
use
silicon iron anodes.
ASME
Amer
ican Society of Mechanical Engineers.
e ASME publishes standards for the
fabr
ication of propane tanks.
B
Backfi ll
e white powder inside a bagged anode that surrounds the metal ingot.
Bac
kfi
ll
consists
of
75% gypsum,
20%
bentonite and 5% sodium sulfate.
In
usage,
bac
kfi
ll is designed to
low
er electrical resistance between the anode and surrounding soil and extend anode life.
Bag
ged Anode
A
zinc or magnesium anode encased in a cloth bag and surrounded by
bac
kfi
ll
consisting
of
gypsum,
bentonite
clay and sodium sulfate.
Bentonite
V
olcanic clay used as an absorbent to absorb water in an anode.
40
Cathodic
Protection
-
Vocabulary List
C
Cathode
e engineering term given to any metal to be protected by an anode.
Mor
e specifi
cally,
metal
that is “reduced”
(not
oxidized) and receives electrons from an
anode
in a corrosion cell reaction.
Cathodic
Protection
A
procedure used to protect buried steel from corrosion by
using
anodes.
Cathodic
Protection Specialist
A
person certifi
ed by
the
National Association of Corrosion Engineers (N.A.C.E.) as
qualifi
ed to solve
corr
osion problems using cathodic protection principles.
Coatings
T
ough,
chemic
ally
iner
t materials designed to protect metal from contact with soil.
Coatings
must prevent penetration by
water
,
o
xygen,
chemic
als (including fertilizer),
mild
acids,
and
resist mechanical abrasion from rocks,
ear
th movements,
and
tree roots.
Coatings must resist biological organisms that may feed on asphalt compounds.
Coke
Breeze
Black granular carbon from coal or petroleum that is placed around an anode in
impr
essed current (rectifi
er) systems.
It
is designed to lower the resistance between the
anode
and the earth.
Connecting
Lug
A
bolt welded to a propane tank by
the
tank fabricator used to connect the anode wire to
the
tank.
Copper
Sulfate
e blue crystals dissolved in the distilled water solution in a copper sulfate electrode
(half-cell).
Copper
Sulfate Electrode
A
copper rod enclosed in a plastic tube fi
lled with distilled water and copper sulfate
cr
ystals.
In
usage,
it
has an electrical connection on one end and a porous ceramic tip on
the
other,
and
is used in conjunction with a voltmeter to measure the stored voltage of a
metal
in contact with earth,
water
or other electrolyte in a tank-to-soil potential test.
Cor
rosion
e electrochemical reaction that occurs when metal is buried or exposed to an electrolyte.
41
Cathodic
Protection
-
Vocabulary List
Corrosion cell
e components required for corrosion to occur form
a
“corrosion cell.”
A corrosion cell
consists
of three components:
A
metallic path for electric current.
•
An
electrolyte
•
An
electrical potential between two metallic objects.
•
Corr
osion cells can exist between two diff
erent metals (such as steel and copper),
betw
een
tw
o diff
erent types of the same metal (such as between the head and the shell of a tank)
or
between two stress areas of the same metal (such as between the welded and non-
w
elded areas of a tank).
Installing
an anode on a steel tank or line creates a corrosion cell in which the installer
c
an determine which metal will corrode (the
anode)
and which metal will not corrode
(the
tank or line).
D
Direct Current (DC)
Electr
ical current that fl
ows continuously and does not fl
uctuate between positive and
negativ
e.
Batter
ies,
r
ectifi
ers and anodes all produce direct current.
In
usage,
in
a corrosion
cell
consisting of an anode and a buried tank,
the
DC current fl
ows from the surface of
the
anode,
thr
ough the earth,
to
the surface of the tank.
Dielectr
ic Union
A
connector in a metallic pipe incorporating “O”
r
ings and rubber or plastic gaskets,
installed
to physically
pr
event one metal from touching the other.
In
usage,
these
fi
ttings
ser
ve
to
isolate the metal being protected from dissimilar metals,
electr
ical currents,
and
undergr
ound objects not requiring protection.
Dome
e rounded top to an underground propane tank that houses and protects the
m
ultivalve© on the tank.
42
Cathodic
Protection
-
Vocabulary List
E
Electrical Isolation
S
eparating underground pipes and tanks from other underground and aboveground
str
uctures.
Without electrical isolation,
anodes
may be trying to protect well casings,
cit
y
water
systems,
electr
ical grids and other underground metal.
Electrode
Most
often means “copper sulfate electrode”
or
“half-cell electrode.”
It
can be used to
descr
ibe an “anode”
or
a “cathode”
in
a corrosion cell.
Electrol
yte
S
oil or water through which DC
curr
ent fl
ows from a buried anode to a cathode such as
a
buried tank.
In
usage,
anodes
must be buried or submerged in the electrolyte in order to
pr
otect the tank or line.
Electrons
S
ub-atomic particles that create electric currents that fl
ow along the wire from an anode
to
a tank.
Exother
mic Weld:
A
convenient brazing process used to connect anode wires to tanks or
pipes.
e weld metal consists of copper oxide fl
akes and fi
nely ground aluminum starting
pow
der.
It
takes some experience to make an exothermic weld.
Anode wires must always
be
welded to a special welding pad or other non-pressure surface of an ASME tank.
Two
common brands of exothermic welding are Cadweld
®
and ermoweld
®
.
F
G
Galvanic Anode
e term given to magnesium or zinc anodes that provide galvanic protection.
Galvanic Protection
e process of using a galvanic anode metal to protect another metal from corrosion.
Galvanic Series
A
list of metals and metal alloys
arranged
according to their corrosion potential from the
metal
most likely to corrode to the metal least likely to corrode (also known as the EMF
S
eries).
e list most often has magnesium at the top of the list with gold or similar metal
at
the bottom of the list.
43
Cathodic
Protection
-
Vocabulary List
H
Half-Cell
Another
term used for the copper-sulfate electrode.
H-1 Alloy
Anodes
containing zinc and aluminum purposely added to magnesium.
S
imilar to the
AZ-63
alloy or “Grade A alloy.”
I
Impressed Current System
A
cathodic protection system using a rectifi
er that converts Alternating Current (AC)
f
rom the electric utility into Direct Current (DC).
Impr
essed current systems are typically
many
times more powerful galvanic systems.
Impressed
Current Anode
An
anode used with a rectifi
er in an impressed current cathodic protection system.
Impr
essed current anodes are typically
high
silicon cast iron buried in coke breeze
bac
kfi
ll.
Insulated
A
term used interchangeably with “isolated”
to
describe the state of being electrically
separated
from another structure.
Insulated
fl
ange
S
ee dielectric or insulated fi
tting
above.
Ion
An
electrically
charged
atom or group of atoms.
Examples
are sodium and chloride atoms
that
break apart when salt dissolves in water.
S
oil and water contain thousands of ions of
var
ying chemical compositions which all conduct electric current through soil.
J
K
L
44
Cathodic
Protection
-
Vocabulary List
M
Magnesium Anode
e most common galvanic anode used to protect buried tanks or piping.
Magnesium
anodes
are available in many shapes and sizes.
Milliamps
(Ma)
A
measurement of how much current (amperes) is fl
owing in a circuit.
A
milliamp equals
1/1000
of an ampere.
Gal
vanic anodes generate a few milliamps to 200 milliamps of
curr
ent depending on soil conditions.
Multival
ve©
e location inside the dome where a dielectric union would be installed to separate
copper
tubing from the steel tank.
Connecting
lugs are often located on the riser below
the
multivalve©.
N
N.A.C.E. (National Association of Corrosion Engineers)
A
professional association of engineers and other people involved
in
corrosion protection.
N
ACE develops and publishes standards for cathodic protection.
O
P
Protective Coating
S
ee “coating”
above
Q
45
Cathodic
Protection
-
Vocabulary List
R
Rectifi er
e power supply for an impressed current cathodic protection system.
It
converts
alternating
current (AC) power into direct current (DC) power.
Reference-Cell
Another
name for the copper-sulfate electrode.
Resistivit
y
e term used to describe how well soil,
water
or other electrolytes conduct electric
curr
ent.
Clay
and highly mineralized soils that have a low resistivity to current fl
ow
ar
e considered “high corrosion potential soils.”
D
ry desert sand has a high resistivity to
curr
ent fl
ow and is considered “a
low
corrosion potential soil.”
e unit of measure for soil,
water
or other electrolyte resistance is “ohm-centimeter.”
R
ubber Boot
e protective covering for the tip of a copper sulfate electrode.
It
keeps the tip from
dr
ying out and must be removed before taking a tank potential reading.
R
ust
e iron oxide byproduct of the corrosion process on steel.
As
a verb,
“rust”
descr
ibes the
pr
ocess of atmospheric oxidation of steel aboveground,
and
can be used to describe the
aggr
essive corrosion of steel underground.
S
Sacrifi cial Anode
Gal
vanic anodes waste away when producing electrical current to protect buried tanks
and
pipes,
ther
efore the name “sacrifi
cial”
anode
.
Sacr
ifi
cial
Protection
e process of protecting a structure using a sacrifi
cial anode as opposed to an impressed
curr
ent anode.
S
oil Resistivity
S
ee “Resistivity”
above
46
Cathodic
Protection
-
Vocabulary List
T
Tank-to-Soil Potential
e DC
v
oltage reading taken between a tank and a copper sulfate electrode using
a
voltmeter.
e reading is recorded in volts or in millivolts.
A
minus (-) sign should
pr
ecede the number because the direct current voltage is understood to be negative.
F
or
example: -1.55
volts (V) can be written minus 1550 millivolts (mV)
U
Underground Wire Connector
A
wire connector fi
lled with a silicon compound and designed to splice wires
undergr
ound or in the dome of an underground tank.
P
lain wire connectors must never
be
used when splicing anode wires.
Union
A
connecting device used to connect two separate joints of pipe together.
V
W
X
Y
Z
Zinc Anode
Z
inc anodes are commonly used to protect tanks and pipes buried in areas where the
gr
oundwater is salty or brackish.
Cathodic Protection Quiz
49
Cathodic
Protection
-
Cathodic Protection Quiz
Cathodic Protection Quiz
1.1
1. Underground propane tanks and metallic piping are subject to an aggressive form of
r
usting due to wet ground containing natural and man-made chemicals.
is
process
c
an cause pits or holes in the tank which could release propane into the ground that
could
migrate into a crawl space or basement.
What is the name of this form of rusting?
_____________________________________________________________________
1.2
2. W
hat is the term used to describe the process of protecting an underground ASME
pr
opane tank by making it a cathode?
_____________________________________________________________________
3. W
hat is the fi
rst line of defense against corrosion of a tank or pipe?
_____________________________________________________________________
1.3
4. What are two ways of cathodically protecting underground propane tanks and piping?
1. ___________________________________________________________________
2. ___________________________________________________________________
5. An
important point to remember is that Cathodic Protection can extend the life of an
underground propane tank by helping to prevent ______________________ and rust.
2.1
6. What are the three most commonly used anodes in the propane industry?
1. ___________________________________________________________________
2. ___________________________________________________________________
3. ___________________________________________________________________
50
Cathodic
Protection
-
Impressed Current Overview
7. What type of anode would work best in brackish or salty groundwater? ____________
8. W
hat type of anode would work best in dry or sandy soil where you need a driving
voltage of -1.75 volts? ___________________________________________________
9. W
hat type of anode is used in the majority of underground conditions found in the
U.S. and has a voltage of -1.5 volts? ________________________________________
10.
What is a typical voltage of unprotected steel in a propane tank? _________________
11.
What is the minimum voltage steel needs to be protected from corrosion? _________
12. ________________
fl
ows from an anode through a wire to the tank.
13. ________________
fl
ows from an anode through the earth to a tank.
14.
e voltage of an anode or tank is measured in ____________________
15. Curr
ent fl
ows from the __________________ to the _______________ in the soil.
16.
Is a tank with a voltage of -1.5 volts protected? _____________
17.
Is a tank with a voltage of 1.5 volts protected? ____________
18.
Is -1.00 volts better than -0.85 volts on a tank? _______
19. In the process of protecting a tank with an anode, what is the cathode? _________
2.2
20. Anodes should be placed ______________or ______________ a tank.
2.3
21. _____________ should be added to an anode to make it work better.
22.
e anode wire is attached to a ________________ on the tank.
23.
In desert or semi-dry areas of the country,
a
__________________ can be placed next
to
the anode so that it can be watered.
24.
After the underground propane tank is in place,
it
is important to ______________
any
defect to the tank coating per manufacturer’s
instr
uctions to avoid an unnecessary
drain on the anode.
51
Cathodic
Protection
-
Impressed Current Overview
2.4
25. Steel tanks must be isolated from bare _____________ service lines in the dome.
26.
What is the term used to describe the separation of steel tanks and bare copper
service lines? ________________________ _________________________
27.
What is installed on the gas piping at the building regulator to isolate the metallic
service line from the building’s underground copper and steel water pipes, the electric
utilit
y ground grid or a water well casing? ________________ ________________
28. In the past, it was common to install bare copper or coated steel service lines to a
house
.
Without dielectric isolation in the dome,
a
tank anode will try to protect both
the
________________ and the _______________which will consume the anode
sooner
.
29.
Tank anodes can also protect coated metallic service lines to a house by
shif
ting
the
steel tank’s
potential
from -0.50 volts to a minimum -0.85 volts.
Uncoated
bare
__________
gas tubing is diffi
cult to protect because the anodes have to shift the
v
oltage from -0.20 volts to a minimum -0.85 volts.
2.5
30. What two components are used to test the cathodic protection on a tank or its
metallic
piping?
1.
_________________________________
2.
_________________________________
2.6
31. When taking a tank-to-soil potential test, you can get a good stable reading by adding
_____________wher
e the copper sulfate electrode is placed on the ground.
32. To read a tank-to-soil potential, you must have the voltmeter set on the 2 volt or the
_______
D.C.
v
olt scale.
33. When taking a reading, one wire is connected to the _____________ and the other
wir
e must connect to the _______________.
34.
How many readings should you take around a residential underground tank? _______
35.
What is the typical voltage of a magnesium anode? _______
52
Cathodic
Protection
-
Impressed Current Overview
36. What is the typical voltage of a copper service line? _______
37.
What is the minimum voltage needed on a tank or metal pipe? _______
38.
When taking a tank to soil potential test on a cathodically protected underground
pr
opane tank and you get a low reading,
list
fi
ve
things
that may be the result of the
low
reading.
1.
______________________________________________________
2.
______________________________________________________
3.
______________________________________________________
4.
______________________________________________________
5.
______________________________________________________
2.7
39. How many reasons can you list for a voltage reading to be zero?
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
40.
What would cause a tank potential reading to be -0.20 volts? ______________
41.
What method can be used to attach a new anode to an old underground propane
tank?
______________________________________________________________
3.1
42. Galvanic magnesium anodes are used on residential tanks. What type of system might
be
used on a large commercial tank larger than 4,000 gallons? _______________
_______________.
43.
If you could see the current from a magnesium anode,
it
would illuminate a tank like
the
light from an ordinary light bulb.
Which anodes illuminate a large tank like a
bank
of stadium lights? _____________________ ____________________
53
Cathodic
Protection
-
Impressed Current Overview
44. A magnesium anode has the power of a 1 volt battery. Where does the power come
f
rom with an impressed current anode? _______________________
45. Resistance in the ground such as dry soil is like smoke that blocks the current
(“
light”) from an anode.
is causes the tank potential to be low.
List
two options to
getting
more current to fl
ow through the high resistance soil (“smoke”) to a tank.
1. ____________________________________
2.
____________________________________
3.2
46. Impressed current rectifi ers convert alternating current to direct current, and the input
and
output voltage can be _________________________ to your health.
47. Can a magnesium anode harm a tank, pipe or unrelated structure? _____
3.3
48. To verify if a rectifi er is on, you should check the output voltage with a
___________________.
Answer Key
57
Cathodic
Protection
-
Answer
Key
Answer Key
1.1
1. Underground propane tanks and metallic piping are subject to an aggressive form of
r
usting due to wet ground containing natural and man-made chemicals.
is
process
c
an cause pits or holes in the tank which could release propane into the ground that
could
migrate into a crawl space or basement.
What is the name of this form of
r
usting?
Corrosion
1.2
2. W
hat is the term used to describe the process of protecting an underground ASME
pr
opane tank by making it a cathode?
Cathodic Protection
3. What is the fi rst line of defense against corrosion of a tank or pipe? Coatings
1.3
4. What are two ways of cathodically protecting underground propane tanks and piping?
1. Sacrifi cial Anodes
2. Impressed Current
5. An important point to remember is that Cathodic Protection can extend the life of an
undergr
ound propane tank by helping to prevent
corrosion and rust.
2.1
6. What are the three most commonly used anodes in the propane industry?
1. High Potential Magnesium
2. Magnesium Alloy
3. Zinc
7. What type of anode would work best in brackish or salty groundwater? Zinc
58
Cathodic
Protection
-
Answer Key
8. What type of anode would work best in dry or sandy soil where you need a driving
v
oltage of -1.75 volts?
High Potential Magnesium
9. W
hat type of anode is used in the majority of underground conditions found in the
U
.S.
and
has a voltage of -1.5 volts?
Magnesium Alloy
10. What is a typical voltage of unprotected steel in a propane tank? -0.50 volts
11.
What is the minimum voltage steel needs to be protected from corrosion?
-0.85 volts
12. Electrons fl ows from an anode through a wire to the tank.
13.
Direct Current fl ows from an anode through the earth to a tank.
14.
e voltage of an anode or tank is measured in
DC Volts.
15. Curr
ent fl
ows from the
anode to the tank in the soil.
16.
Is a tank with a voltage of -1.5 volts protected?
Yes
17. Is a tank with a voltage of 1.5 volts protected? Yes
18. Is -1.00 volts better than -0.85 volts on a tank? Yes
19. In the process of protecting a tank with an anode, what is the cathode? The Tank
2.2
20. Anodes should be placed under or beside a tank.
2.3
21. Water should be added to an anode to make it work better.
22.
e anode wire is attached to a
threaded bolt or pigtail wire on the tank.
23.
In desert or semi-dry areas of the country,
a
watering pipe can be placed next to the
anode
so that it can be watered.
24. After the underground propane tank is in place, it is important to touch-up any
defect
to the tank coating per manufacturer’s
instr
uctions to avoid an unnecessary
drain
on the anode.
59
Cathodic
Protection
-
Answer
Key
2.4
25. Steel tanks must be isolated from bare metal service lines in the dome.
26.
What is the term used to describe the separation of steel tanks and bare copper
service lines? Dielectric Isolation
27.
What is installed on the gas piping at the building regulator to isolate the metallic
ser
vice line from the building’s
undergr
ound copper and steel water pipes,
the
electric
utilit
y ground grid or a water well casing? Dielectric Union
28. In the past, it was common to install bare copper or coated steel service lines to a
building
.
Without dielectric isolation in the dome,
a
tank anode will try to protect
both
the
tank and the pipe which will consume the anode sooner.
29.
Tank anodes can also protect coated metallic service lines to a building by
shif
ting
the
steel tank’s
potential
from -0.50 volts to a minimum -0.85 volts.
Uncoated
bare
copper gas tubing is diffi cult to protect because the anodes have to shift the voltage
f
rom -0.20 volts to a minimum -0.85 volts.
2.5
30. What two components are used to test the cathodic protection on a tank or its
metallic
piping?
1.
Volt Meter
2. Copper Sulfate Electrode
2.6
31. When taking a tank-to-soil potential test, you can get a good stable reading by adding
water where the copper sulfate electrode is placed on the ground.
32.
To
r
ead a tank-to-soil potential,
y
ou must have the voltmeter set on the 2 volt or the
20 D.C. volt scale.
33.
When taking a reading,
one
wire is connected to the
Copper Sulfate Electrode and
the
other wire must connect to the
Multivalve.
34.
How many readings should you take around a residential underground tank?
4
60
Cathodic
Protection
-
Answer Key
35. What is the typical voltage of a magnesium anode? 1.5 Volts
36. What is the typical voltage of a copper service line? -0.20 Volts
37. What is the minimum voltage needed on a tank or metal pipe? -0.85 Volts
38. When taking a tank to soil potential test on a cathodically protected underground
pr
opane tank and you get a low reading,
list
fi
ve
things
that may be the result of the
low
reading.
1.
In the dome, is there copper tubing leading from the regulator?
2. Is there a dielectric or insulating union between the copper tubing and the tank?
3. Is the coating on the tank peeling off or non-existent in the dome?
4. Is there a steel service pipe and no dielectric union in the piping at the building?
5. Is there electrical continuity between the multivalve© and the pipe into the
building?
Additional Answers
6. The anode wire may not be securely connected to the tank.
7. The anode may have been buried still inside its plastic bag.
8. The anode may be dry.
9. The anode may be old and have been consumed.
10. The anode may have been too small (1 lb, 3 lb, 5 lb. anodes are too small).
11. The anode may be lying up against the opposite side of the tank.
12. Is there a plastic liner under decorative rock or bark between the electrode
and
the tank? If so, punch a small hole with a pencil and pour water at the
hole
before taking the reading again.
13. Are you connected to a metal dome and not the multivalve©?
61
Cathodic
Protection
-
Answer
Key
2.7
39 How many reasons can you list for a voltage reading to be zero?
1. Start with the voltmeter. Is it on?
2. Is the battery good?
3. Have you taken off the rubber boot on the copper sulfate electrode?
4. Have you set the voltmeter switch to the d.c. volt scale?
5. Have you connected one lead wire to the copper sulfate electrode?
6. Have you connected the other lead wire to the multivalve© securely?
7. Does your copper sulfate electrode have a blue liquid in it?
8. Have you set the electrode fi rmly on the ground?
9. Have you poured a glass of water on the ground if the ground is dry?
10. Are your lead wires and their connections good?
40. What would cause a tank potential reading to be -0.20 volts?
Copper service line not isolated from the tank
41.
What method can be used to attach a new anode to an old underground propane
tank?
Band clamp on the steel riser
3.0
42. Galvanic magnesium anodes are used on residential tanks. What type of system might
be
used on a large commercial tank larger than 4,000 gallons?
Impressed Current
43. If you could see the current from a magnesium anode, it would illuminate a tank like
the
light from an ordinary light bulb.
Which anodes illuminate a large tank like a
bank
of stadium lights?
Impressed Current
44. A magnesium anode has the power of a 1 volt battery. Where does the power come
f
rom with an impressed current anode?
Electric Utility
62
Cathodic
Protection
-
Answer Key
45. Resistance in the ground such as dry soil is like smoke that blocks the current
(“
light”) from an anode.
is causes the tank potential to be low.
List
two options to
getting
more current to fl
ow through the high resistance soil (“smoke”) to a tank.
1.
Add water to the anode
2. Add more anodes
3.2
46. Impressed current rectifi ers convert alternating current to direct current, and the input
and
output voltage can be
dangerous to your health.
47.
Can a magnesium anode harm a tank,
pipe
or unrelated structure?
No
3.3
48. To verify if a rectifi er is on, you should check the output voltage with a voltmeter.
Skills Evaluation Cathodic Protection
(Galvanic Protection Only)
o
Student explained the basics of corrosion – what leads to the corrosion of an
unpr
otected tank or metallic piping.
(
What is corrosion and how does it happen?)
o
Student explained the principles of how galvanic protection protects underground
tanks
and metallic piping.
(
What is galvanic protection and how does it work?)
o
Student followed proper safety procedures while installing cathodic protection by
compl
ying with company policy.
o
Student performed pre-installation preparation, including referring to company
polic
y,
c
alling the national hotline (811) or the local one-call system.
o
Student properly selected and installed a sacrifi cial anode on an underground ASME
pr
opane tank.
o
Student properly isolated piping and above ground system from an underground
ASME
propane tank.
o
Student demonstrated how to correctly activate a sacrifi cial anode.
o
Student demonstrated how to determine if test equipment is working properly and
pr
operly tested:
o
An unprotected tank
o
A tank not adequately protected
o
A properly protected tank
o
Student demonstrated how to troubleshoot when getting improper voltage readings
while
testing an anode.
o
Student demonstrated how to properly retrofi t an unprotected underground ASME
pr
opane tank with a new anode.
__________________________________
__________________________________
S
kill Evaluator (print)
S
kill Evaluator (signature)
__________________________________
__________________________________
S
tudent Name (print)
S
tudent Signature
__________________________________
Date
CERTIFICATE OF INSTRUCTION
CATHODIC PROTECTION
Company providing training: _________________________________________
Company receiving training: _________________________________________
is is to certify that ________________________________________________
has successfully completed the Cathodic Protection
Quiz and
Skills Evaluation
e training was conducted at: _______________________________________
________________________________________________________________
On ________________________________
Full Name of Person Receiving Training
Name
City State Zip
Month Day Year
o
o
DVD
e DVD video on Cathodic Protection is designed to allow you to watch exactly
what you want, when you want to watch it.
To begin, there is a “Welcome” from Stuart Flatow of the Propane Education &
Research Council that will play automatically as soon as you insert the DVD in
your DVD player on your computer. However, note your computer must be set to
“automatic play” for this to happen. is enclosed DVD is also formatted to play
in your television’s DVD player.
At the completion of the “Welcome,” is the main menu. From this menu you can
choose to watch the entire Cathodic Protection program from beginning to end
without a pause, or you can choose to watch any of the fi fteen program
segments that are found in Sections 1, 2, and 3, in any order you choose.
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WWWPROPANESAFETYCOM
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