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 NORM in the Petroleum Industry

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عدد المساهمات : 7
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تاريخ التسجيل : 08/12/2010
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مُساهمةموضوع: NORM in the Petroleum Industry   الإثنين 12 نوفمبر - 23:55

NORM in the Petroleum Industry: An Introduction to General Understanding of Naturally Occurring Radioactive Materials (NORM).



Introduction

Objectives
After completing this module, you should be able to:


  • Define radiation and radioactivity.
  • Describe the occurrence and characteristics of NORM in the petroleum industry.
  • Identify radium and radon hazard areas in petroleum facilities.
  • List NORM safety procedures.
  • Explain the proper handling and disposal of NORM waste.




Radiation Fundamentals

Overview
To help understand NORM, some of the fundamentals of radiation are reviewed. Simple depictions of atoms and radioactive processes are used throughout the module for illustrative purposes only.


Atoms
All material is composed of atoms. Atoms are made up of protons, neutrons, and electrons. Electrons, which appear here in red, have a negative charge and orbit about the nucleus. The nucleus is a positively charged mass at the center of the atom. It is composed of protons and neutrons. Neutrons,
shown here as blinking white spheres, are the neutral component of the
nucleus. That is, a neutron has no electrical charge. Protons
are positively charged particles which, together with neutrons, make up
the nucleus of an atom. The protons are shown in blue on the screen. Protons and neutrons are about the same size. Protons and neutrons are 1800 times larger than electrons. This comparison of relative size shows that an atom is extremely small. The relative size of an atom compared to an orange is about the same as the relative size of an orange compared to the earth.


Radioactive Decay
Although most
atoms are stable and do not change with time, some atoms are unstable
and undergo radioactive decay with the emission of radiation. For
example, radium, a solid material, undergoes radioactive decay with the
emission of alpha particles and changes into radon gas. This graph shows the decay rate of radioactive material as it changes to its daughter product. The vertical axis indicates the amount of radioactive material remaining in the original sample. The horizontal axis is time.


Half-Life
The decay rate of radioactive material is discussed in terms of 'half-life'. For
example, if 100 grams of a radioactive element has a half-life of one
year, then after a one year period, half the amount, or 50 grams, will
remain. At the end of the following year, 25 grams will remain, and so on. Each radioactive element has its own decay rate, measured in half-life. To see the broad range of decay rates, the decay profiles of three elements, uranium, radium-226, and radon, are presented. Pay particular attention to the time scale used on the horizontal axis. Click each button to see the decay profiles.


Types of Radiation
When radioactive material undergoes decay, radiation is emitted. Three types of radiation will be discussed:


  1. alpha,
  2. beta,
  3. and gamma.
Alpha radiation is composed of two neutrons and two protons. The protons give the alpha particles a positive charge. Alpha radiation is stopped by a sheet of paper, or by the surface of human skin. Beta particles are electrons, very small negatively charged particles. They are stopped by a thin layer of aluminum foil. Unlike alpha and beta radiation, which are particles, gamma radiation is an electromagnetic energy ray. Gamma radiation is capable of passing through a variety of material, such as quarter-inch steel.


Origin of NORM

Definition of NORM
This section defines NORM and explains how NORM contamination forms in the petroleum industry. Most people think of radioactive materials in the context of nuclear power generation. However,
this is not the material we call NORM, which stands for 'naturally
occurring radioactive material' and is present as a contaminant in the
petroleum industry. Naturally occurring radioactive elements are radioactive materials that are found in the Earth's crust. They include such elements as uranium, thorium, potassium, radium, and radon. Click each button to see the amount of material present in a 3-foot layer of dirt.


Radiation in Reservoir Water
Thorium and uranium are generally insoluble in reservoir fluids, and remain in the reservoir during production. Radium,
a radioactive decay product of uranium and thorium, can dissolve in
formation waters and can be carried into the production system. A thorium atom decays by emitting an alpha particle. This creates a radium atom, which may dissolve in the formation water and be carried with the produced fluids.
A serious problem in the petroleum industry is the formation of radioactive scales in production piping. Radium co-precipitates with barium sulfate, which is commonly deposited as scale in oil fields throughout the world. This
photograph shows a cross-section of heavily scaled production piping
from the North Sea. This scale was found to be radioactive with radium
from the reservoir.


Radiation in Reservoir Gas
In a gas
reservoir, radon gas, which is a decay product of radium, is produced
with the natural gas and contaminates the gas handling system. Radon is a by-product of both thorium and uranium. As in liquid producing reservoirs, thorium and uranium are immobile in the reservoir.


Occurrence and Characteristics

Overview
Gas handling facilities can become contaminated with NORM in the form of radon and radon decay products. Production piping and vessels in water handling surface facilities can become contaminated with radium NORM.


Water Handling System
NORM scale and sludge is a potential hazard at all water handling facilities. It occurs in production tubing, wellheads, flow lines, manifolds, pressure vessels, pipelines, and settling ponds. Used pipes and equipment in storage may have been contaminated with NORM scale and sludge. Any
scale found around pipe racks and the inside or outside of pipes should
be considered contaminated with NORM unless surveys prove otherwise. Scale
and sediments in active or inactive sludge pits may be contaminated
with NORM. A survey should be conducted to determine the extent of
contamination. The soil in the vicinity of pipe reaming areas should be evaluated for NORM contamination. Waste piles or sludge in used vessels should also be checked.


Gas Handling System
Radon, which is
preferentially soluble in propane and ethane, concentrates in the
propane and ethane product streams leaving natural gas processing
plants. Radon itself is not a
serious health hazard, but decays in about 30 days to long-life
radioactive products that can contaminate natural gas handling
facilities for a long time. The
decay products of radon range from short-life metals, decaying in three
to four hours, to long-life metals, which are a hazard for hundreds of
years. Equipment that has been used
in natural gas processing plants may be highly contaminated with
long-life decay products of radon and should be checked.
Radon decay
products are solid materials that can either plate out on or impregnate
the interior surfaces of piping and equipment, particularly where there
is a change in the flow stream direction. The
decay product of radon that is of most concern to the industry is a
form of lead which is a solid material that settles out of fluid forming
radioactive films on pipe walls. These materials can also migrate into the metal.


NORM Surveys

Overview
NORM
contamination in petroleum facilities is found by surveying with the
appropriate radiation detection equipment and procedure. Most NORM contamination can be found with the use of survey meters. The author is shown in these photos making a survey in a gas liquids plant. Maintaining good records is very important in a NORM control program.


External Surveys
Radium contamination is found by surveying piping and equipment with either a scintillation counter or a geiger counter. The more contamination, the higher the meter reading. External surveys of equipment will detect radium contamination. However, internal radon and radon decay product contamination cannot be detected by external surveys.


Internal Surveys
In the interior
of piping, vessels, and other equipment, contamination with radon and
radon decay products can only be located with internal NORM surveys. The survey meter must be held immediately adjacent to the expected contamination. Samples of loose material, scale, and sludge should be taken and sent to the laboratory for NORM content analysis.


Radioactivity Measurement
The two most
important parameters in characterizing the quantity of NORM are the
radioactivity, measured in picocuries, and the radioactive dose,
measured in microrems. Radioactivity is measured in terms of picocuries. A picocurie is a very small unit corresponding to 2.2 radioactive disintegrations per minute. NORM contamination found in the petroleum industry can contain levels as high as hundreds of thousands of picocuries per gram. More typical contaminations, however, are less than 1000 picocuries per gram.


Radioactivity Dose Measurement
The radiation absorbed by the human body is measured in REMs, which stands for Radiation Equivalent Man. We are constantly being exposed to radiation in everyday life, from sources in the atmosphere and in the ground. Radiation sources from the atmosphere include cosmic rays, x-rays, and high-energy protons and electrons from space. Radiation sources from the ground include uranium, thorium, radium, and potassium.
Some radiation is actually generated from radioactive materials present in living things, including the human body. Cigarettes
contain significant quantities of radioactive materials. Tobacco
plants concentrate radioactivity from the soil into their leaves. When
the leaves are made into cigarettes, the radioactivity is inhaled into
the body. An individual smoking one pack of cigarettes per day can
receive a considerable radiation exposure. Radiation
exposure due to medical and dental diagnostic procedures such as x-rays
contribute significantly to the body's annual radiation exposure. Human
bodies contain significant quantities of natural radioactivity
including uranium, thorium, radium, carbon-14, and a form of potassium.


Regulations
Low levels of NORM are exempt from regulation controls because they present no health hazard to the public. The exemption level for radium is generally 5 to 30 picocuries per gram of material. The natural background level in soil is usually 1 to 2 picocuries per gram, but in some areas exceeds 5.
As of January 1st, 1994, regulations for NORM control are being developed as shown on this map. Four states in the USA have regulations in effect. Several other states and three Canadian provinces are currently developing regulations and standards. Several European countries have regulations, as well. In two to five years the entirety of the USA, Canada and Europe will probably have regulations.


Scope of the NORM Hazard

NORM Damage to the Body
This section identifies the extent of the NORM hazard in the oil industry. NORM is a health hazard to the human body when it is ingested or inhaled. It is a relatively insignificant hazard to humans as long as it is external to the body. Although
gamma rays are very penetrating, NORM-generated gamma rays, whether
from external or internal sources, cause relatively minor damage to the
body.
The alpha particles from the radioactive decay of NORM external to the body will not penetrate the skin. Alpha
particles from NORM ingested or inhaled into the body, however, can
cause very significant damage to the lining of the lungs or to bone
cells. When NORM-contaminated dust particles or aerosols are inhaled, the NORM can attach itself to the sensitive linings of the lungs. The
subsequent emission of alpha particles during radioactive decay can
cause significant localized damage, potentially resulting in malignancy. NORM
ingested into the stomach can be carried by the bloodstream to various
organs, particularly the bone tissue, where the alpha emission can cause
considerable damage and be the source of leukemia or bone cancer.


Mode of Radiation Damage
NORM within the
body can emit alpha particles in close proximity to cells. These cells
can be damaged or destroyed by the alpha emission from the NORM. Radium can cause malignancies in the bones and lungs. Radon and radon decay products can also cause lung cancer if inhaled. Possible malignancies are caused by alpha particles disrupting the genetic material in cells. Here, a DNA strand is fragmented by an alpha particle.


Comparative Risk Factors
The health risk from NORM is small when compared to exposure from other health risks. This graph shows, for example, that smoking 20 cigarettes per day reduces life expectancy by 2370 days, or about 6-1/2 years, whereas exposure to 150 millirems per year for 30 years in a typical pipe yard reduces life expectancy by only 4.5 days.
The human body
is exposed to many sources of radiation. This graph shows that NORM
exposure is relatively low when compared to other sources. For
example, the safe exposure level for radiation workers is 5000
millirems per year, yet the typical oilfield worker is exposed to only
150 millirems per year of NORM radiation. If
a pipe yard worker receives 1 millirem of radiation per hour of NORM
waste for 10 hours per week, what is his annual radiation dose assuming
he takes two weeks of vacation?


Working with NORM

NORM Supervision
Every facility with a potential for NORM should have a specially trained Safety Radiation Officer, or SRO, appointed. The SRO conducts monitoring surveys which are a key element in keeping NORM contamination under control. The SRO implements the necessary industrial hygiene program for working safely with NORM.
The safety radiation officer is responsible for monitoring the removal, storage, and disposal of NORM waste. Keeping and maintaining records of NORM exposure, contamination, and disposal are an important responsibility of the SRO.


NORM Industrial Hygiene
A good industrial hygiene program is required in order to work safely with NORM.


  • The use of respirators is the most important industrial hygiene procedure to be used when working around NORM. Respirators will ensure that NORM is not inhaled into the body.
  • Self-contained air packs may be necessary when working with high levels of radon contamination.
  • Gloves should be worn at all times when working with NORM to prevent contamination of the hands.
  • Any open cuts or wounds should be bandaged to prevent NORM from entering the body.
  • Eating and drinking are not allowed when working around NORM contamination.
  • A shower may be required before leaving work if the work area is particularly dusty.
  • Clothing worn when working with NORM
    contamination, particularly in dusty areas, should be changed before
    leaving the work area. Special disposable clothing may be required.
  • There can be no smoking when working near NORM contamination.
Radiation exposure is minimized by time, distance, and shielding. The shorter the time spent in an area contaminated with NORM, the less the exposure. Also, the further one is away from the NORM contamination, the less the exposure. Any material between personnel and sources of NORM acts as shielding and reduces exposure.


Equipment Opening Procedures
Specific procedures should be followed when opening vessels and equipment which may be contaminated with NORM. The vessels or equipment should be vented to remove any radon or NORM dust which may be present. Take precautions to prevent fire and avoid breathing the vented gases. After
venting, the hatches can be opened, but the vessels or equipment should
not be entered immediately. Personnel should stand back from the
opened hatches. A delay of three
hours before entering the vessels or equipment is suggested to allow
decay of the short-life decay products of radon. A radiation survey should be made with a survey meter to determine the extent of NORM contamination. Suppress dust if necessary. When opening vessels and equipment which may be contaminated with NORM, observe the NORM safety vows:


  1. ventilation,
  2. open,
  3. wait,
  4. survey,
  5. and suppress.




Mechanical Removal
The removal of
NORM contamination requires that specific industrial hygiene practices
be followed. This may require specially trained personnel. The
removal of NORM contamination should be supervised by the safety
radiation officer who will ensure that the work is done safely and will
make radiation surveys of the project. If possible, avoid using methods such as sandblasting, which will add to the volume of NORM waste that must be disposed. Dust-raising operations should be minimized. Use wet grinding in a completely enclosed system if possible. Any water used in NORM cleaning must be collected and handled as NORM waste.
Since water
used for cleaning may be contaminated with NORM, it may be necessary to
filter the water to remove the NORM before disposal. Any material used in the mechanical removal of the NORM, such as rags, must be collected and handled as NORM waste. Industrial hygiene practices must be followed to insure working safely with NORM.


Leaving NORM in Place
NORM
contamination does not necessarily have to be removed. It is relatively
safe to personnel as long as it is inside vessels and tubing. Scale in tubular goods need not be removed unless it restricts flow. NORM can generally be left in tubulars and vessels unless they are to be released for unrestricted use.


NORM Waste Handling

Containment
NORM waste must be properly contained. Waste materials removed from vessels and equipment should be kept in sealed barrels. Vessels and equipment contaminated with NORM should be kept sealed. NORM waste must not be put on the ground. The ends of piping should be capped. External scale on tubular goods should be wrapped to prevent contamination of the environment.

Storage
NORM wastes should be kept in a controlled-access area that is surveyed regularly, and a good paper record maintained. Warnings should be posted that radioactive material is stored in the area.

Transport
Most NORM wastes will not require US Department of Transportation permitting. However, when transporting such items as contaminated tubular goods, the pipe should be capped at the ends. It may also be necessary to wrap the pipe to prevent contaminating trucks or roadways. NORM-contaminated soil may be transported in covered trucks or railroad cars.

Disposal
There is no good approved option for NORM disposal yet. Three
methods are currently in use that puts NORM back near the area from
which it originated. These probably offer the best protection to the
environment. There are two
regulated and licensed landfills for the disposal of NORM in the U.S.
One is in Utah and the other is in Washington state. Disposal in landfills is very expensive, costing more than 500 dollars per barrel.
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NORM in the Petroleum Industry
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