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GP 16-19-01 Electrical - Electrical Heat Tracing July 2004

Electrical - Electrical Heat TracingGP 16-19-01

Scope

This Global Practice (GP) covers basic requirements for the design, layout, and installation of heat tracing

equipment and auxiliary facilities for powering and alarming to be installed in petroleum handling andprocessing plants and in petrochemical plants.

Upstream For ExxonMobil Use Only Version 3.0.0

Page 1 of 29 ExxonMobil Development Company

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Table of Contents

1. Required References...................................................................................................6

1.1. GPExxonMobil Engineering Practices...........................................................6

1.2. ExxonMobil Data Sheets..................................................................................6

1.3. IECInternational Electrotechnical Commission..............................................6

1.4. IEEEInstitute of Electrical and Electronics Engineers....................................6

1.5. NFPANational Fire Protection Association.....................................................6

2. General and Design Conditions.................................................................................7

2.1. Use...................................................................................................................7

2.2. Heat Tracing Types..........................................................................................7

a) It withstands high temperature and corrosive atmospheres. ............................7

b) It has good physical strength but shall not be used in an area where it will bebent away from the heated equipment in order to access that equipment... .7

3. Design Requirements................................................................................................10

3.1. General Design Requirements.......................................................................10

c) Heat up times shall be as follows:.....................................................................11

1. Instruments and associated lines in all services: 46 hours............................11

2. Onsite, 2 in. and smaller process lines in critical service: 810 hours.............11

3. Onsite, 3 in. and larger process lines and equipment in critical service

equipped with low temperature alarms wired to a control room: 1824hours.............................................................................................................11

4. Non-critical onsite lines and equipment............................................................11

d) A critical electrical heat tracing service is a service where a freeze-up couldcreate an unsafe condition or cause a unit upset/shutdown........................11

e) In general, onsite piping is considered non-critical, and the 1824 hour heat-uptime is acceptable.........................................................................................11

f) On large lines, long lines, or similar high capacity electrical requirements forheat-up, the heat-up time may be lengthened in conjunction with a lowtemperature alarm to reduce the size of the electrical tracing system

required. This heat-up may be lengthened to what is reasonable andpractical for application.................................................................................11

3.2. Design Requirements.....................................................................................11

3.3. Complete Design Requirements....................................................................12

g) One drawing for each circuit.............................................................................12

UPST For ExxonMobil Use Only Version 3.0.0


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bb) Main breaker...................................................................................................16

cc) Temperature controller....................................................................................16

dd) Over-temperature controller............................................................................16

ee) Contactors.......................................................................................................16

ff) Open circuit detection and alarm......................................................................16gg) Short circuit detection and alarm.....................................................................16

hh) If specified, an over current and/or over voltage contact(s) (must be providedand have ground fault protection where the controller does not provide it). 16

5. Control, Distribution, and Alarm..............................................................................17

5.1. Control............................................................................................................17

5.2. Distribution......................................................................................................18

5.3. Alarms.............................................................................................................19

a) Loss of voltage at the end of line, or undercurrent on line, for every circuit.Circuits shall not alarm when tracing is not on.............................................19

b) Failure of temperature sensing unit or controller..............................................19

i) This is required for every temperature control device in the system.................19

2. Thermostat systems require separate thermostat............................................19

3. Thermocouple or RTD systems can use one sensor as long as open or shortcircuit alarms are included in controller........................................................19

4. A separate thermostat is required if the controller does not alarm in failedmode.............................................................................................................19

c) Ground fault trip.................................................................................................19

d) Total loss of voltage to the system....................................................................19

e) High temperature...............................................................................................19

f) Low temperature................................................................................................19

g) If specified, over current and/or over voltage....................................................19

6. Installation..................................................................................................................19

6.1. General...........................................................................................................19

6.2. Identification...................................................................................................21

6.3. Skin Effect Heat Tracing Installation..............................................................21

7. Testing........................................................................................................................22

a) When reeled cables are received at the job site...............................................22

b) After installation prior to insulation being installed............................................22

c) After installation prior to energizing for the first time.........................................22



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8. Data Sheet..................................................................................................................22

Appendix: Completion of Data Sheet........................................................................23

Scope.............................................................................................................................23

A1. Page 1...................................................................................................................23

A2. Page 2...................................................................................................................23

A2.1. Sizing Information: Lines 1 through 16...................................................23

A2.2. Details of Heat Tracing after Sizing: Lines 12 through 31......................24

a) Enter T- for thermostat......................................................................................24

b) Enter TO- thermostat on overall ambient..........................................................24

c) Enter C- for controller........................................................................................24

d) Enter A- for always on.......................................................................................24

Record of Change.........................................................................................................25

Attachment: Purpose Codes Definitions...................................................................29



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1. Required References

This Section lists Practices and Standards that are generically referenced and assumed to be a part of this

document. Unless otherwise specified herein, use the latest edition.

1.1. GPExxonMobil Engineering Practices

GP 03-19-02 Upstream Piping Fabrication, Erection, Inspection, and Testing

GP 16-13-01 Field Installation and Testing of Electrical Equipment

GP 50-01-02 Winterizing and Heat Tracing

1.2. ExxonMobil Data Sheets

ExxonMobil DataSheets Data Sheet Home Page

T161901C01 Electrical - Electrical Heat Tracing - Pipelines - Customary Units

T161901M01 Electrical - Electrical Heat Tracing - Pipelines - Metric Units

1.3. IECInternational Electrotechnical Commission

IEC TR 61423 Heating Cables for Industrial Applications

IEC 62086 Electrical Apparatus for Explosive Gas Atmospheres - Electrical

Resistance Trace Heating

1.4. IEEEInstitute of Electrical and Electronics Engineers

IEEE 515 Standard for the Testing, Design, Installation, and Maintenance of

Electrical Resistance Heat Tracing for Industrial Applications

IEEE 622B Recommended Practice for Testing and Startup Procedures for Electric

Heat Tracing Systems for Power Generating Stations

IEEE 844 Recommended Practice for Electrical Impedance, Induction, and Skin

Effect Heating of Pipelines and Vessels

1.5. NFPANational Fire Protection Association

NFPA 70 National Electrical Code


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2. General and Design Conditions

The design, layout, and installation of heat tracing equipment and auxiliary facilities for powering and

alarming to be installed in petroleum handling and processing plants and in petrochemical plants shall be

in accordance with the requirements of this GP, unless superceded by more stringent local regulations.

2.1. Use

Electric heat tracing (EHT) or other kind of warming equipment shall be used to maintain the minimum

temperature of fluid contents in process equipment and piping subject to freezing, congealing, separation,

excessive increases in viscosity or forming water by condensation. If product heat-up is required or over-

temperature can degrade a product, it shall be noted on the ExxonMobil Data Sheets for this GP.

2.2. Heat Tracing Types

2.2.1. Steam Tracing

Steam tracing is covered inGP 50-01-02. Before choosing a type of heat tracing, the benefit andliabilities of both electrical heat tracing and steam tracing shall be considered. The following statements

are some things that should be considered in regards to steam tracing.

1) Steam is typically easier to fix, commonly requires less initial design, and frequently has a lower

installed cost than that of electrical heat tracing.

2) Steam shall not be considered for nonmetallic pipe or products that will be degraded at the

temperature of the steam.

3) Steam tracing is often, but not always, the better choice for areas requiring temperatures above 100F

and locations where warmed equipment needs to be accessible for maintenance.

4) Steam tracing is cost-effective where high sheath temperatures of EHT and low auto-ignition

temperatures are required due to area classification.

2.2.2. MI/SI Cable

Mineral Insulated (MI) cable will be considered for all areas.

1) MI cable has long life characteristics.

a) It withstands high temperature and corrosive atmospheres.

b) It has good physical strength but shall not be used in an area where it will be bent away from the

heated equipment in order to access that equipment.

2) Initial installed cost of MI cable is high and it requires detailed initial design information to purchase.

3) Silicone Insulated (SI) heater cable is not a preferred product of ExxonMobil and may be consideredonly if the cable(s) being investigated meet the requirements contained in IEEE 515 and with

ExxonMobil approval.

2.2.2.1. Components

This constant wattage type system shall consist of a solid metal sheath containing one or two conductors

separated by mineral (or silicon, if approved) insulation. This mineral insulation shall be magnesium


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oxide. The conductors will be resistance type heating elements with operating voltages up to 600 V.

Thermostatic control shall be used with this system.

2.2.2.2. Sheath Types

The cable outer sheathing material shall be capable of operating under high temperature and highly

corrosive conditions. The sheath shall be stainless steel or Inconel (Alloy) 825. Owner's strong

preference is for Inconel 825. However, if a stainless steel sheath is used, it shall be limited to a sheathtemperature of 427C (800F) and a process maintain temperature no higher than 260C (500F).

2.2.3. Constant Wattage Parallel Bus

Constant Wattage Parallel Bus cable uses two buses with spiraled resistance wire connected between

them at intervals along the cable.

1) If the EHT system is engineered properly and this cable is installed correctly, this product has a

reliable life.

2) Cable sections can burn out if they are crossed over one another (doubled up) or they are handled

roughly.

3) Do not use on small-bore pipe that could freeze if a 2-ft section were to lose heat. The failure of[multiple] heating "zones" is hard to detect with this cable. The result of this loss of heater capacity

results in "cold spots."

2.2.4. Constant Wattage Series Cable (excluding MI and Skin Effect Type)

Constant Wattage Series cable, like MI, uses series resistance buses and must be closely designed for theapplication.

1) It is a cost-effective method to heat long existing lines and has good reliability.

2) It is typically not cost-effective for lengths less than 500 ft.

3) Whenever practical, the cable shall be installed with three wires and connected three-phase.

2.2.5. Self Regulating Polymer Cable

Self-regulating polymer cable is the least installation-sensitive of all the electric types and requires the

least initial design.

1) It performs well in complex piping arrangements, such as instrument level columns.

2) This type cable has an average installed cost, can be cut to length at site, and has a low energy usage.

3) A disadvantage is that, if not specified and installed properly, it has the shortest life of all the different

cable designs. However, if done properly, it will last at least 10 to 15 years before replacement is

required.

2.2.6. Power Limiting Parallel Bus CablePower Limiting Parallel Bus is a parallel heating cable formed by a coiled resistor alloy heating element

wrapped around two parallel bus wires. It is called power limiting because it reduces power output as

ambient temperature increases.



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1) This heater cable is a high output power cable that is rated for high maintain and exposure

temperatures (not as high as MI, however). This product can also be cut to length at the job site,

making installation simpler.

2) This product must be specified with a metal braid covered by an outer polymer base jacket for

corrosion resistance.

3) This product is fairly new and therefore requires the approval of an ExxonMobil Electrical Engineerbefore use.

2.2.7. Skin Effect Heat Tracing

1) The Skin Effect Heat Tracing system is a constant wattage system consisting of a ferromagnetic,

small diameter, carbon steel pipe or heat tube. This tube is connected to the process pipe being heat

traced by means of straps, heat transfer cement, skip welding, or continuous fillet weld (on both sides

of pipe interface). An insulated copper cable is contained inside the heat tube and is bonded to the

pipe at the end. The "inner wall" of the heat tube becomes the return path of the circuit. The current

flowing in the heat tube causes it to become the heating element. There is no current or voltage on

the "outer wall" of the heat tube due to the "proximity effect" of the current caused by the internal

wire's magnetic field.2) Skin effect heating is physically similar to a single conductor in rigid steel conduit. While current

flows in the inner surface envelope, the outer surface of the heating tube is at ground potential and

there is no shock hazard (per NFPA 70 and ANSI/IEEE 844). However, where voltages higher than

600 V are used, high voltage warning signs shall be provided at all pull and junction boxes and at

intervals along the line.

3) This system may be installed both below ground and above ground and may be grounded without

affecting cathodic protection systems.

4) The Skin Effect system is suitable for pipelines, long rundown lines, and transfer lines (600 m [2000

ft] or longer) where very few valves and flanges are present.

5) When welding the heat tube to piping, care shall be taken to avoid locations where moisture cancollect in the piping and cause corrosion. Welding to high-strength, low-alloy piping shall be done

only with prior ExxonMobil approval. All welding shall conform to GP 03-19-02.

6) Installed cost is very high on existing pipe, but can be cost-effective on new installations with limited

turns and valving. It may also be cost-effective on some existing installations such as long transfer

lines. This is due to the need for fewer power connections, limiting the associated conduit and

wiring, and being able to cut down on the needed control points.

2.2.8. Blanket Electric Heaters

Steam is the preferred way to heat a vessel or tank. However, small tanks, nonmetallic, or units

containing sensitive materials that will degrade if heated to available steam temperatures are candidates

for blanket electric heaters.

2.2.9. In-Line Heating

In-line heating of gas and liquids shall be done with circulation type MI heating elements. These types ofheaters shall often be used when small streams of gas need to be reheated after expansion and a steam

exchanger cannot be justified.


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3. Design Requirements

3.1. General Design Requirements

3.1.1. Areas of Use

Electrical heat tracing is recommended under the following circumstances:

1) Where nonmetallic pipe requires heat tracing.

2) Where steam tracing temperatures may degrade the product or corrode the line.

3) Where pour point protection or dew point protection is specified.

4) Where precise temperature control of the line is required.

3.1.2. Approval

1) Electrical heat tracing cable and all ancillary materials shall be approved and listed for use in Class 1,Division/Zone 2 locations as a minimum, even though the location may be unclassified.

2) Electrical heat tracing cable and ancillary materials shall be approved for the purpose and area

classification by Factory Mutual (FM), Underwriters Laboratories (UL), or other recognized testing

agency.

3) The heat tracing cable shall not exceed 80 percent of the ignition temperature of the gas or vapor that

could be present (using degrees Celsius). The cable shall have a certified maximum temperature class

(T rating).

4) Class 1, Division/Zone 1 rated heater cables and components are higher cost (materials and labor)

than their lesser rated counterparts. Equipment manufacturer approval of all Division/Zone 1

applications is required prior to installation.

3.1.3. Instruments

1) All instruments, taps, gauges, and piping associated with the same process line may be traced with a

common circuit if appropriate. When more than one instrument is connected to a common circuit,

each instrument shall have a local disconnecting means.

2) Instruments that are connected to associated process lines with process sensing lines not exceeding

one process line diameter in length may be heat traced with the heat tracing cable used for the process

line. Consideration shall be given to making all process instruments a separate circuit with separate

temperature control (i.e., RTD).

3.1.4. Capacity

1) Heat tracing circuits shall be designed for 125 percent of heat loss at worst ambient conditions with90 percent of rated voltage. For piping less than 3 in. (760 mm) in diameter, the heat tracing circuits

shall be designed for 135 percent of heat loss. However, the 135 percent figure can be relaxed with

Owner's permission if over heating of the liquid is a potential safety problem (i.e., safety shower).

2) Special consideration shall be given to heat tracing requirements for pumps. Pumps generally

represent a large heat sink. The heat loss for pumps in critical service shall be determined by finite



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element analysis and consultation with the heat tracing system manufacturer. The minimum heating

capacity requirement shall be 200 percent of the heat loss determined by standard calculation methods

or 125 percent of the heat loss determined by finite element analysis.

3) Spiral wrapping of heat tracing cable in EHT applications is not allowed; instead, higher wattage

cable or multiple runs shall be used.

4) The heat tracing cable output under the most severe conditions shall not result in a systemtemperature that exceeds the maximum allowed by the process. Controllers with a high temperature

cutout may be employed if needed.

5) High heat loss at pipe flanges, valves, dead legs, support shoes, and other appurtenances shall be

compensated by use of additional lengths of heat tracing in accordance with the manufacturer's

instructions.

6) The heat-up times must be given special attention.

c) Heat up times shall be as follows:

1. Instruments and associated lines in all services: 46 hours

2. Onsite, 2 in. and smaller process lines in critical service: 810 hours

3. Onsite, 3 in. and larger process lines and equipment in critical service equipped with low

temperature alarms wired to a control room: 1824 hours

4. Non-critical onsite lines and equipment

d) A critical electrical heat tracing service is a service where a freeze-up could create an unsafe

condition or cause a unit upset/shutdown

e) In general, onsite piping is considered non-critical, and the 1824 hour heat-up time is acceptable.

f) On large lines, long lines, or similar high capacity electrical requirements for heat-up, the heat-up

time may be lengthened in conjunction with a low temperature alarm to reduce the size of the

electrical tracing system required. This heat-up may be lengthened to what is reasonable and

practical for application.

3.1.5. Moisture prevention

The following minimum requirements shall be met to maximize the design life and integrity of the

installation.

1) In offshore environments, non-hygroscopic insulation shall be used.

2) Heat trace penetrations shall be via dedicated bushings or conduits.

3) All heat trace penetrations shall be sealed to avoid moisture ingress.

3.2. Design Requirements

Before detailed design begin, an ExxonMobil Electrical Engineer shall review:

1) Insulation "K" factors and thicknesses to be used.

2) Local conditions used in heat loss formulas such as ambient temperature variations, startuptemperature, and wind speed.

3) Sheath/surface temperatures for Division/Zone 1 and 2 areas.



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4) Temperature maintain requirements, product heat-up time if required, and location of dead legs

requiring individual temperature control.

5) Any over-temperature condition that may degrade the product, be a safety concern, or lead to

excessive corrosion.

6) Control and alarm philosophy.

7) Tracing types to be considered.

8) Voltage level used (120 VAC and 230/240 VAC grounded system is only approved method for all

except Skin Effect EHT; others shall be approved).

9) Design deliverables per Section 3.3.

3.3. Complete Design Requirements

1) Piping isometrics showing complete tracing. (With approval of an ExxonMobil Electrical Engineer,

this may not be needed, or the requirement may be reduced for some types of tracing.) Full

isometrics shall show, as a minimum, the following:

g) One drawing for each circuit.h) Location of temperature sensor, cold junctions, power connection, splice, and terminations.

i) All flanges, valves, pipe supports, tap lines, drains, pumps, vessels, nozzles, and instruments.

j) Length of cable on pipe and any extra for above items.

k) Circuit information and current requirements at minimum ambient startup and design

temperature.

l) Operation design conditions including area classification.

m) Maximum heat trace length that can be protected by the nominated circuit protection.

2) Complete the ExxonMobil Data Sheets for this GP or approved vendor sizing program for all tracing,including the maximum sheath temperature for hazardous conditions, tracing type, amount used at all

valves, shoes, flanges. For a detailed explanation of requirements, see Section 8 and the ExxonMobilData Sheets for this GP.

3) Heat tracing panel schedule listing equipment to be traced.

4) Connection diagram.

5) Junction box and thermostat/control sensor location drawing.

6) Alarm system wiring diagrams.

7) Installation details for the heat tracing system.

8) Commissioning Data Sheet for startup.

9) Bill of Material (BOM) of EHT materials required.

3.4. Special Design Requirements for Arctic Climates

1) Special consideration shall be given to maintenance of heat trace systems in these climates. When

operators need to work on this equipment they are often dressed in apparel that is not conducive to

working on small parts and in tiny spaces. It may also be advisable to procure special maintenance



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products such as portable maintenance sheds/tents (perhaps with heaters) which will allow operators

to warm up the immediate environment surrounding whatever device they are working on.

2) When equipment, signs, and maintenance access ways are designed, particular attention shall be paid

to the large amounts of snow falls and snow drifts that can be expected in these regions. In areas

where snow is going to be allowed to accumulate, signs shall be posted both at a height higher than

the highest snow level expected and also on the equipment itself.3) Inrush currents in most heater cable in cold temperatures are much higher than at warmer

temperatures. This fact must be accounted for when choosing the heater cable and associated

protective devices/settings.

4) The effects of large quantities of ice must be considered. Two particular problems are its weight and

the problem of falling ice.

4. Specifications

4.1. General Vendor Requirements

Specifications for the installation and testing of electrical heat tracing systems shall be prepared by theVendor and submitted for ExxonMobil approval.

4.2. MI/SI Cable

1) Cable shall be resistance wire surrounded by compressed mineral insulation (or silicon dioxide if

approved) with a metallic sheath of stainless steel or Inconel 825 (Inconel 825 is preferred).

2) Cold sections/leads shall be 3 ft to 7 ft long and shall have a stainless steel or Inconel sheath. The

line side of the cold section shall have a factory applied moisture-proof connection with 1/2 in. or3/4

in. male conduit connector and a minimum 9 in. power leads.

3) Maximum cable lengths shall be 150 ft within process areas and 250 ft once outside of [crowded]

process areas. All cable shall be factory fabricated and shipped complete for installation. Factory hot

and cold splices shall be brazed or silver soldered.

4) Each cable shall be shipped in an individual package with a stainless steel cable tag which includes

the catalog number, circuit voltage, length and wattage.

5) The entire cable shall be rated for 600 V.

6) Each cable shall be capable of field bending to an inside radius of six times the cable diameter

without damage.

4.3. Constant Wattage and Power Limiting Parallel Bus Cable

1) Heating cable shall have nickel plated copper bus wires insulated with a fluoropolymer. The bus

wires shall be able to provide service up to 250 ft at designated application voltage without any loss

of cable output wattage due to voltage drop. Maximum lengths shall be reviewed by an ExxonMobil

Electrical Engineer.

2) A protective braid of plated copper shall be applied with an overall fluoropolymer jacket.



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3) Termination, splice, and power connection kits shall be part of the system and approved for the area

classification. All kits shall be designed for access above the final insulation.

4) A full description of the cable construction and installation requirements shall be provided with the

Vendor's bid.

5) The heating cable shall be supplied on reels and cut to length at the job site. Minimum reel length

shall be specified on the purchase order.

6) Cable insulation shall be rated for exposure temperatures of 204C (400F) while off and continuous

121C (250F) while on. Insulation shall also be rated for 600 V.

7) All systems shall be approved for installation in Class 1, Division/Zone 2 atmospheres.

4.4. Self-Regulating Polymer Cable

1) Heating cable shall consist of an extruded conductive polymer core or a nonconductive core with

wrapped polymer fiber elements between two copper bus wires and covered with a fluoropolymer

jacket. A nickel or tin-plated copper braid shall be installed above this jacket with another overall

fluoropolymer jacket.

2) The bus wires and cable in general shall be capable of being used up to a length of 240 ft at the

designated application voltage without falling under rated cable output wattage due to voltage drop

(i.e., published unit wattage's verses temperature curve values).


temperatures of 121C (250F) while on. Insulation shall also be rated for 600 V. Exposure to high

temperature shall not cause a loss of more than 10 percent of rated output during cable life.

4) "Low temperature" self-regulating cable (maintain temperatures of 150F and exposure temperatures

of 185F) shall only be used with approval of ExxonMobil Electrical engineer. This is because it

inevitably gets mistakenly installed on pipes that require steam clean out.

5) Termination, splice, and power connection kits shall be part of the system and approved for the areaclassification. All kits shall be designed with proper access through the final piping insulation and

have proper external nameplates such that operations personnel can easily locate the devices in spite

of insulation.

6) A full description of the cable construction and installation requirements shall be provided with theVendor's bid.

7) The heating cable shall be supplied on reels and cut to length at the job site. Minimum reel lengthshall be specified on the purchase order.

8) All systems shall be approved for installation in Class 1, Division/Zone 2 areas as a minimum.

4.5. Constant Wattage Series Cable1) Cable shall consist of multiple resistance cables with fluoropolymer insulation, plated copper jackets,

and overall fluoropolymer jackets.


temperatures of 121C (250F) while on. Insulation shall also be rated for 600 V.



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3) Cable shall come cut to length with factory installed end terminals and 5 ft non-heated lead

connection. Lead connections shall have stainless armor with 1/2 or3/4 in. conduit connections on end

and an additional 9 in. of lead wire.

4) Each cable shall be shipped in an individual package with a stainless steel cable tag which includes

the catalog number, circuit voltage, length and wattage.

5) Cable system shall include all hardware required and be approved for Class 1, Division/Zone 2 areas.

4.6. Skin Effect Heat Tracing

1) The Vendor shall provide all design documentation and hardware required which shall include but

not be limited to:

n) System design

o) Transformers

p) Controls

q) Pull boxes

r) Copper cable with high temperature insulation

s) Copper plated terminals

t) Splice kits

u) Heat tube

v) Terminal boxes

w) Power feed boxes

x) Cable lugs and connecting hardware

y) Thermocouple or RTD with assembly for surface contact on heated pipe

2) The heating system may be supplied as part of an entire system including process pipe, insulation,

and heat tube.

3) The system shall be approved for installation in a Class 1, Division/Zone 2 area.

z) The heating system shall be designed to provide a balanced three-phase load.

aa) The Vendor shall provide detailed installation and test procedures for the heating system

including welding specifications for all items.

4.7. Blanket Heaters

1) Blanket heaters shall be silicone rubber with embedded metal ground grid.

2) They shall be approved for installation in Class 1, Division/Zone 2 locations and require ground fault

protection the same as other systems.

3) Maximum application temperature is 121C (250F).

4.8. In-Line Heaters

1) The heating chamber shall be, as a minimum, Schedule 40 pipe with ASME code stamp for greater

than or equal to piping classification.

2) A drain connection shall be an integral part of the body to allow draining of the chamber.



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4.8.1. Heating Bundle

1) The internal, direct contact heating bundle shall be constructed of tubular elements with at least

stainless steel sheathed heaters welded into a round steel flange. A center well shall project midway

into the center of the bundle and shall contain a thermocouple or RTD set for the bundle over-

temperature protection. The well shall comply with ExxonMobil Instrument Guides for the service.

2) The tubing type shall be specified by type, size, wall thickness, and quantity. The heater shall be

specified as electric or steam. The heating element and the tube(s) shall be cabled together to allow

for uniform thermal expansion and contraction. Electric heater and the tubes shall be continuously

wrapped by heat reflective tape (heat barrier). The bundle then shall be wrapped again with adequate

non-hygroscopic glass fiber insulation. The bundle shall then be covered by an extruded polymer

jacket.

4.8.2. Terminal Box

1) The tubular element terminals and the thermostat leads shall be brought out into a terminal box of

cast construction (other box constructions if approved) that is on the opposite side of the round

flange. The elements shall be connected together for a balanced three-phase load and labeled as T1,

T2, and T3.

2) If specified, the terminal box shall have a space heater.

4.8.3. Controls

1) Controls shall be in an enclosure located remotely, which is properly rated for its location. Minimum

enclosure types shall be NEMA 1 with gasket for climate controlled indoor locations, NEMA 12 for

non-climate controlled indoor locations, NEMA 4X for non-classified outdoor locations, NEMA 7 for

hazardous indoor locations, and explosion-proof NEMA 4X for hazardous outdoor locations.

Controls shall include:

bb) Main breaker

cc) Temperature controllerdd) Over-temperature controller

ee) Contactors

ff) Open circuit detection and alarm

gg) Short circuit detection and alarm

hh) If specified, an over current and/or over voltage contact(s) (must be provided and have ground

fault protection where the controller does not provide it)

2) For units that have wide load requirements, consideration shall be given to SCR control.

4.8.4. Contactors

Contactors shall not be loaded to more than 80 percent of their amperage rating.



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5. Control, Distribution, and Alarm

5.1. Control

1) Freeze protection tracing shall be turned on and off with an ambient sensing thermostat set at 7C

(45F).

2) Process temperature shall be maintained with controllers. Pipe temperature shall be measured with

RTD or thermocouple. Alarms shall be initiated by the controller on low temperature. In instances

where installing a controller is not practical, dual thermostats shall be allowed (with approval), one

for control, one for alarm (however, thermostats should not generally initiate alarms).

3) Each instrument shall have an individual thermostat; however, instruments may be heated using pipe

heat tracing line. Calculations shall be presented to ExxonMobil Engineer showing minimum and

maximum temperatures of instrument equipment using this method. Instruments shall be insulated

with a preformed flexible cover. If a ridged insulating box is used, then a cast heater with thermostat

that does not interfere with accessibility of the instrument shall be installed.4) A heating system that has dual heating range requirements shall be designed so that the heating range

can be selected on a two-position switch.

5) Special attention shall be paid in order not to over-heat piping, especially where safety related items

like eye washes and safety showers are concerned. "Process control" methods such as a

thermostat/RTD sensing line temperature shall be used to limit liquid temperature where personnel

safety could be an issue.

5.1.1. Circuits

1) Either controllers or circuit breakers shall provide 30 mA ground fault protection on all circuits.

2) Circuits for lines handling different process fluids shall be supplied from separate circuits.3) Lines that may concurrently contain flowing and static fluid, or be out of service, shall be separately

controlled.

4) Generally, circuits for dead-end lines for draining, venting, flushing, and normally closed bypass shall

not be combined with the same control for circuits used for main process lines. However, circuits for

those lines not exceeding three times the main process line diameter in length may be combined withthe same control. When considering EHT circuits on process applications, all conceivable flow paths

should be independently measured and controlled (including bypasses around control valves).

5) Provisions shall be made in the circuitry to facilitate removal of pumps or valves without affecting the

heat tracing on associated equipment or process lines. Where practical, heat tracing cables for pumps

and valves shall be provided with local disconnecting means to facilitate removal without affecting

operation of heat tracing on connected process lines. When using a removable cover, install tracing

on the wall of the cover rather than attaching to pump or valve.

6) When self-limiting heat tracing cables are specified, it is possible that the criteria noted in Items 3through 5 may be waived, provided that none of the design temperature requirements are jeopardized.

7) In all cases, manufacturer's recommendations shall be strictly followed for the installation of electrictrace cable.



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8) The installed electric trace cable shall allow maintenance activities, including valve, pump, and

instrument removal, without damage to the trace integrity.

5.1.2. Thermostats

1) Thermostats shall be provided as part of the heat tracing system and shall have sufficient contacts to

energize the tracing circuit and to alarm for failures. Contacts shall be loaded at less than 80 percentof published amperage ratings.

2) All hot legs shall be opened by the thermostat or a contactor shall be used to provide the necessary

contacts.

3) The thermostat manufacturers name and temperature range shall be submitted for approval.

4) All thermostats shall be factory calibrated and tested for proper contact operation before shipment.

5) Thermostat capillary tubing shall be protected by an armor sheath.

6) For piping that is traced for water freeze protection, a main contactor and ambient sensing thermostatmay energize all of the heat tracing at once.

7) No more than six cable circuits shall be operated from one thermostat for other than ambient service.

5.2. Distribution

1) Heat tracing systems shall have designated transformers and panel boards for proper distribution.

2) The transformer shall have a three-phase 120/208 VAC secondary grounded neutral. For large

diameter pipe with high heat requirements, a three-phase 480 or 380 VAC grounded neutral system

may be used (transformer still required). Other voltage levels may be used as approved by

ExxonMobil Engineer and if new voltage level(s) is common to both the facility and the local region.

3) Smaller systems may be connected to existing panels with local site approval.

4) Transformers shall have nominal plus four 21/2 percent taps, two above and two below nominal

voltage (these taps may vary with Skin Effect Heat Tracing systems).

5.2.1. Independent Operation

The heating system shall be designed such that each pipeline heating system may be independently

operated, turned on or off, or locked out, without affecting other pipeline heating systems.

5.2.2. Location

1) Wherever possible, panels shall be located inside in a nonhazardous location.

2) All outdoor panels, junction boxes, and control enclosures shall be rated NEMA 4X as a minimum.

5.2.3. Breakers and Circuit WiresBreakers and circuit wires shall be sized in accordance with Article 427 of the NEC (NFPA 70). For

international applications, breakers and circuit conductor sizes shall comply with the appropriate local

regulations for short circuit protection and earth fault detection in the applicable hazardous area.

1) Breakers shall be sized for a maximum load of 100 percent of rated current at the minimum designambient.



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2) Normal operating load for circuits shall not exceed 80 percent of breaker rating.

3) No single circuit shall be greater than 50 amperes or the maximum allowed by the hazardous

certification for the heat tracing.

4) Where controller does not provide ground fault, breakers shall be 30 mA GFI type.

5) The system shall be designed with 25 percent spare branch breakers and 25 percent spare systemcapacity.

6) Breakers need to be selected and set to properly handle heater cable inrush currents.

5.3. Alarms

1) All heat tracing systems shall alarm to a manned location. If tracing is in a remote location where

alarming is not feasible, then a local beacon is acceptable if approved by site operations and

maintenance.

2) Summary alarms to manned locations are allowed as long as each alarm is separately annunciated at

the remote point. If the alarm is acknowledged at a remote point, it shall still indicate, but shall clear

the summary alarm for subsequent failures.3) Heat tracing requires the following alarms to be separately indicated:

a) Loss of voltage at the end of line, or undercurrent on line, for every circuit. Circuits shall not

alarm when tracing is not on.

b) Failure of temperature sensing unit or controller.

i) This is required for every temperature control device in the system.

2. Thermostat systems require separate thermostat.

3. Thermocouple or RTD systems can use one sensor as long as open or short circuit alarms are

included in controller.

4. A separate thermostat is required if the controller does not alarm in failed mode.

c) Ground fault trip.d) Total loss of voltage to the system.

e) High temperature

f) Low temperature

g) If specified, over current and/or over voltage

6. Installation

6.1. GeneralDetails not covered by this GP or local requirements shall be per the Manufacturers details. Any

conflicts shall be reported to an ExxonMobil Project Electrical Engineer.



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6.1.1. Heating Cables

1) Heating cable shall be installed to permit ease of maintenance. Flexibility, to allow heating cable to

be moved away from areas where maintenance shall be required, shall be provided by accordion type

loops in cable or separate circuits that can be totally removed before equipment is serviced. Where

bends are required in the heating cables, the minimum bending radius specified by the Manufacturer

shall not be exceeded.

2) For installations 66C (150F) or below, heating cables shall be fastened to pipes with fiberglass tape

or ty-raps. For MI cable, 1/2 in. wide stainless steel bands shall be used. Tracing is to be attached at

intervals of 2 ft or less (1 ft or less is preferred).

6.1.2. Temperature Sensor

1) Temperature sensing bulbs shall be secured to pipeline with ty-rap or Scotch 27 tape, at least 90

degrees around pipe from any heat tracing. Remove any scale at the contact point prior to

installation. The thermostat shall be installed in a location to provide maximum accessibility and

support for the capillary.

2) The bulb or any temperature sensor shall be located at least 3 ft from any heat sink.3) Thermostats and sensors shall be easily accessible for adjustment and maintenance. Thermostats

shall be mounted on stands and not attached to the process line.

4) The heating cable on pipelines or equipment shall be maintained in continuous contact insofar as

practical in order to maximize heat transfer.

5) Insulating cement shall not cover heating cables. When pumps, elbows, etc. are to be insulated using

insulating cement, the heating cable shall first be covered with aluminum tape to prevent contact

when the cement is applied.

6) When cables are installed on bolted equipment, care shall be taken to provide extra heating while

continuing to allow access to bolts.

7) Heating cables that are external to the thermal insulation shall be protected from mechanical damageby metallic channel or conduit. Particular care shall be exercised where the heating cable passes

through the insulation protection to avoid damage to the cable sheath. Similar care shall be taken at

other locations, such as at valve flanges, where the insulation cover may interfere with heating cable.

6.1.3. Miscellaneous

1) The junction of MI cable hot and cold sections shall have a strap installed on each side of the

junction. Do not bend MI cable within 3 in. of any silver soldered fitting.

2) Sample lines to analyzers shall be pre-assembled tubing bundles with approved heat tracing system.

Control, alarm, and distribution requirements are no different from other tracing systems.

3) Splices and tee connections for branches shall be used only where necessary. Where branches arerequired, the preferred method is to double-back along shortest section of piping (except where

overheating of product is possible).

4) Metallic cladding shall be earthed via dedicated earth straps to ensure earth continuity for operation

of earth fault protection. Earthing straps shall be a minimum of every 5 m.



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5) Drilling and tapping into metallic clad heat trace lines shall not be allowed due to risk of trace

damage.

6) All electric trace cable shall be mechanically protected. This shall be via the insulation and cladding,

conduit or steel angle sections.

7) All metallic components shall be earthed, such that circulating currents are not created.

8) Junction boxes shall be rigidly supported.

6.2. Identification

1) Lead wires from the panel to the pipe tracing shall be marked at the panel and any junction point per

connection drawings.

2) All boxes associated with the heat tracing (power connection, splice, and terminating) shall have a

laminated plastic label listing both the panel and the circuit to which the heat tracing is connected.

3) All panels shall have a laminated tag with the panel number, use (heat tracing), feeder number, and

panel schedule drawing number.

4) All panels shall have a typed weatherproof circuit schedule.

5) MI cable shall have stainless steel tags with catalog number, length, voltage, and wattage indicated

installed on cold section.

6) Caution signs shall be securely installed at electrical traced equipment and at 3 m (10 ft) intervals on

alternating sides of electrically traced pipelines. Caution signs shall be positioned where they arehighly visible to personnel. Electrically traced pipelines on overhead pipe racks shall have the

caution signs installed on the top and bottom.

7) Controllers and thermostats shall have laminated tags with panel number, circuit number, and line

designation.

8) Any items covered by insulation and cladding which may require period maintenance or use shall

have a plastic placard on the outside of the cladding indicating the item's location.

6.3. Skin Effect Heat Tracing Installation

1) Vendor's installation details and test procedures shall be followed.

2) The temperature sensing thermocouple for the system shall be located no more than 15 ft from main

power connection point.

3) The pipe shall be grounded at each end and, at a minimum, every 600 m in between. Ground lugs

welded to the pipe shall extend beyond the insulation jacketing for ground connection. Where a

buried pipeline is cathodically protected, special consideration shall be given to the grounding

system.

4) The Skin Effect Vendor shall approve the length and number of bends in each pull between boxes.

5) Skin Effect tube welded splices between lengths of heated pipe shall be free of weld material inside

and tube ends shall be inspected for burrs before splicing.

6) Terminals on pipes shall be coated with a rust inhibiting, conductive compound before making

connections. Belleville type washers shall be used for all terminations. All terminations shall be

inspected by ExxonMobil before closing the box and installing insulation



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7. Testing

1) For heating cable systems, each cable and each circuit shall be field tested in accordance with the

manufacturer recommendations.

2) An insulation resistance test and a resistance test shall be performed as follows:

a) When reeled cables are received at the job site

b) After installation prior to insulation being installed

c) After installation prior to energizing for the first time

3) A final system test shall require full operation of all heaters for 24 hours with the

thermostats/controllers turned up to energize tracing for the entire period. Current and ambient

readings on each circuit shall be made at beginning and every four hours.

4) Testing of transformers, wiring, and panels shall be perGP 16-13-01.

5) All testing shall be documented and witnessed.

6) All earth fault protective devices shall be tested for tripping current level and opening time prior to

energizing of the circuit.

8. Data Sheet

T161901C01 (see the ExxonMobil Data Sheets for this GP) is for piping only; equipment being traced

shall require individual attention separate from T161901C01. Refer to the instructions in the Appendix to

this GP when completing T161901C01.


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Appendix: Completion of Data Sheet

Scope

T161901C01 may be used for one installation where the page one information does not change; multiple

pages two may be attached. If the area classification, T rating, distribution panel, controller, or thermostat

type or alarm system changes, a separate data sheet shall be required.

A1. Page 1

1) General Section: Required information on area classification and T rating, and local ambient

conditions.

2) Electrical System Information: Required information on system voltage at heat tracing distribution

panel.

3) Control Information: List type of control for individual circuits; one Data Sheet may have a mix of

control methods: always on, thermostat or controllers. Be sure to list the catalog number for each

control type. This section is required for final Data Sheet information; this may be decided when heattrace sizing is performed or Vendor may specify.

4) Reference Drawings: Required for final Data Sheet.

A2. Page 2

General: Lines 1 through 16 ofT161901C01are required to get Vendor bid for heat tracing systems.

A2.1. Sizing Information: Lines 1 through 16

Line 1: The pipe ID or line number is needed to differentiate lines.

Line 2: The isometric drawing number shall be referenced and drawing attached for bid.

Line 3: Heat-up time, if heat-up or melting of process is required, needs to be indicated here.

Line 4: For heat-up or melt, specific gravity and heat are required to determine power input and shall be

indicated here.

Line 5: Minimum and maximum control temperatures of the liquid. The minimum control temperature

would be a low temperature turn-on for thermostat or controller and above actual minimum temperature

for process. Maximum would be turn-off temperature for process heating; for the thermostat, it would be

turn-on plus deadband of the thermostat. This shall be below the maximum control temperature allowed

by the process.


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Line 6: Actual minimum and maximum temperature limits that the process is not to exceed. Lines 5 and

26 shall be within this range.

Line 7: Steamout temperature is the maximum process temperature to which the heat tracing shall besubjected.

Lines 816: Details of pipe configuration. Line 14, for additional heat sinks, shall be given in equivalent

pipe lengths. The foot per item shall be supplied after tracing is sized.

A2.2. Details of Heat Tracing after Sizing: Lines 12 through 31

Lines 1215: Supply the number of feet of tracing to be installed at each heat sink.

Line 17: Calculated heat loss per foot for pipe from sizing program.

Line 18: Calculated maximum temperature for pipe on ambient or always-on systems.

Line 19: Type of tracing specified (self-limiting, MI, etc.)

Line 20: Watts per foot nominal for tracing used with a slash and number of parallel runs needed.

Example: For a pipe needing 12 watts per ft, Vendor may specify three runs of five watts per foot tracing

so entry would be 5/3.

Line 21: Catalog number for tracing used.Line 22: Maximum sheath temperature of tracing to be checked against T rating of system.

Line 23: Total length of tracing in this circuit.

Line 24: Type of control for the circuit reference page 1 catalog number:

a) Enter T- for thermostat.

b) Enter TO- thermostat on overall ambient.

c) Enter C- for controller.

d) Enter A- for always on.

Line 25: Setpoint for controller or thermostat, high and low end. For most thermostats, the high end shall

be the low setpoint plus deadband.

Line 26: Setpoint for low and high temperature alarm.

Line 27: Tag number for alarm, if one exists.

Line 28: Calculated minimum and maximum current for circuit within control parameters. If constant

wattage cable, only one value is required.

Line 29: Setpoint for low voltage or current alarm on circuit. Follow by A or V to indicate which is

being used.

Line 30: Tag number for alarm, if one exists.

Line 31: When panel schedule is developed, enter circuit number here.



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Record of Change

Version 1.0.0 Date: 07/01

Location Action Description

Initial Publish.


Section 2.2.2,

Item 1) a)

Modification a) It withstands high temperature and corrosive and Division 1 areas

atmospheres.

Section 2.2.2.1 Modification Changed the first sentence to read as follows:

The constant wattage system will shall consist of a solid metal sheath ofstainless steel or Inconel containing one or two conductors separated by

mineral or silicon insulation.

Section 2.2.7.2 Modification The first sentence has been changed to read as follows:

The benefits of SECT are as follows. Design shall be done by a given

below. A specialty company shall perform design after piping design is

finalized.

Section 3.1.5 Addition Entire section was added.

Section 3.2,

Item 8

Modification 8) Voltage level used (120V120 VAC and 230/240 VAC grounded

system is only approved method, others shall be approved).

Section 3.3,

Item 1, e) and

g)

Modification/

Addition

e) Circuit information and current requirements at minimum ambient

start up and design temperature.

g) Maximum heat trace length that can be protected by the nominated

circuit protection.

Section 3.3,

Item 2

Modification The last sentence was modified to read as follows:

See For a detailed explanation of requirements, see Section 8 and the

ExxonMobil Data Sheets for this GP for detailed explanation of

requirements.

Section 4.3,Item 2

Modification The second sentence was changed to read as follows:

The bus wires shall be capable of being used able to provide service up to

250 ft at designated application voltage without any loss of cable output

wattage due to voltage drop.

Section 4.4,

Item 7

Addition 7) All systems shall be approved for installation in Class 1, Division 2

areas as a minimum.



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Section 5.1,

Item 2

Modification First sentence changed to read as follows:

2) Process temperature maintain shall be done maintained with

controllers.

Section 5.1,

Item 3


3) Instruments Each instrument shall have their own thermostats but an

individual thermostat; however, instruments may be heated using pipe

heat tracing line.

Section 5.1.1 Addition 7) In all cases manufacturers recommendations shall be strictly followedfor the installation of electric trace cable.

8) The installed electric trace cable shall allow maintenance activities,

including valve, pump and instrument removal, without damage to the

trace integrity.

Section 5.2,

Item 2

Modification Second sentence in Item 2 changed to read as follows:

For large diameter pipe with high heat requirements, a three-phase 480 or

380 Volts AC grounded neutral system can may be used (transformer still

required).

Section 5.2.1 Modification The heating system shall be so designed such that each pipeline heating

system can may be independently operated, turned on or off, or lockedout, without affecting other pipeline heating systems.

Section 5.2.3 Modification/

Addition

Breakers and circuit wires shall be sized in accordance with Article 427

of the NEC. For international applications, breakers and circuitconductor sizes shall comply with the appropriate local regulations for

short circuit protection and earth fault detection in the applicable

hazardous area.

1) Breakers shall be sized for a maximum load of 100 percent of rated

current when turned on at 40F. the minimum design ambient.

2) Normal operating load for circuits shall not exceed 80 percent ofbreaker rating.

3) No one single circuit shall be greater than 30 amperes . Where

ground fault is not provided or the maximum allowed by controller,

breakers will be 30 mA EPD type. the hazardous certification for theheat tracing.

4) Where controller does not provide ground fault, breakers shall be 30

mA GFI type.

5) The system shall be designed with 25 percent spare branch breakers

and 25 percent spare system capacity.

Section 5.3 Addition 5) High temperature

6) Low temperature

Section 6.1.2,Item 5


5) Heating cables shall not be covered by insulating cement. Insulating

cement shall not cover heating cables.



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Section 6.1.3 Addition 4) Metallic cladding shall be earthed via dedicated earth straps to ensure

earth continuity for operation of earth fault protection. Earthing straps

shall be a minimum of every 5m.

5) Drilling and tapping into metallic clad heat trace lines shall be

avoided where possible, due to risk of trace damage.

6) All electric trace cable shall be mechanically protected. This shall bevia the insulation and cladding, conduit or steel angle sections.

7) All metallic components shall be earthed, such that circulating

currents are not created.

8) Junction boxes shall be rigidly supported.

Section 7 Modification 1) For heating cable systems, each cable and each circuit shall be fieldtested in accordance with the Manufacturer's manufacturer

recommendations.

2) An Insulation insulation resistance test and a resistance test shall be

performed on as follows:

a) When reeled cables when are received at the job site, and again after

b) After installation prior to insulation being installed.

c) After installation prior to energization for the first time

Section 7 Addition 6) All earth fault protective devices shall be tested for tripping current

level and opening time prior to energization of the circuit.

Section 8 Modification Last sentence changed to read as follows:

Refer to the instructions in the Appendix to this GP when filling out

completing T161901C01.

Appendix

Scope

Modification T161901C01 can may be used for one installation where the page one

information does not change; multiple page two's pages two may be

attached. If the area classification, T rating, distribution panel, controlleror thermostat type or alarm system changes, a separate data sheet shall be

required.

Appendix Section 1

Modification Last two sentences changed to read as follows:

Make Be sure to list the catalog number for each control type. This

section is required for final Data Sheet information, but; this may not be

decided when heat tracing trace sizing is done performed or Vendor may

be left for the Vendor to specify.

Appendix

Section 2.1

Modification Lines 816: Details of pipe configuration. Line 14, for additional heat

sinks, shall be given in equivalent pipe lengths. The foot per item is to

shall be supplied after tracing is sized.


Global Practice version number and format updated to comply with new

process; however, original publish date remains, and no content was

modified.



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Throughout

GP.

Modifications,

Deletions,

Additions

Multiple general revisions throughout GP.



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Attachment: Purpose Codes Definitions

Code Description

C Assigned to paragraphs containing specifications whose primary purpose is reduced costs.

Reduced cost in this context refers to initial investment cost and does not include Life-Cycle

cost considerations. Life-Cycle cost considerations are captured under reliability,

maintainability, or operability purpose codes.

E Assigned to paragraphs containing specifications whose primary purpose is driven by

environmental considerations. Environmental considerations typically include specifications

intended to protect against emissions/leakage to the air, water, and/or soil. Deviations from the

specifications contained in such paragraphs require formal review and approval according to

local environmental policy.

I Assigned to paragraphs that provide only clarifying information such as Scope statements,

definitions of terms, etc.

M Assigned to paragraphs containing specifications whose primary purpose is to provide for

maintainability of equipment or systems. Maintainability provisions are those that facilitate the

performance of maintenance on equipment/systems either during downtimes or during on-

stream operations.

O Assigned to paragraphs containing specifications whose primary purpose is to assure

operability of equipment or systems. Operability is the ability of the equipment/system to

perform satisfactorily even though conditions are off-design, such as during startups, process

swings, subcomponent malfunction, etc.

R Assigned to paragraphs containing specifications whose primary purpose is to improve or

assure the reliability of equipment or systems. Reliability is a measure of the ability ofequipment/systems to operate without malfunction or failure between planned maintenance

interventions.

S Assigned to paragraphs containing specifications whose primary purpose is avoidance of

personnel or operational safety incidents. Any deviation from the specifications contained in

such designated paragraphs requires formal review and approval according to local safety

policy.

Personnel Safety: Refers to the avoidance of recordable personnel injuries; i.e., burns, cuts,

abrasions, inhalation, or exposure to dangerous substances, etc., thatcould result in medical treatment, restricted work, lost-time incidents, or

fatalities.

OperationalSafety:

Refers to the prevention and control of process releases, fires, explosions,etc.


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