IPE-TM-100-05 — Winterizing Heat Tracing

1. Purpose

This procedure describes the method used to specify Winterizing and Heat Tracing where required in Schedule A Engineering design work.

2. General

The winterizing and heat tracing portion of the Schedule A describes what is required to protect equipment from damage or operability problems due to freezing, congealing, excessive increase in viscosity, or condensation. This procedure includes information on how to establish the objective tracing temperature for different conditions and gives some design considerations for equipment.

3. Responsibility

It is the responsibility of the Design Engineer and Equipment Specialist, with the assistance of the Technology Specialist, to ensure that winterizing and heat tracing requirements are met for a particular project.

Although operating difficulties and shutdowns caused by inadequate winterizing and heat tracing may be very expensive, the cost of providing such protection may also be very high. Considerable judgment is therefore necessary to ensure that the protection provided is appropriate. In some situations, the actual physical layout may preclude the use of tracing on a specific line segment, and the contractor may legitimately request a deviation. These are exceptions for which the contractor must take full responsibility.

4. Definitions

Engineering design specifications sometimes refer to low temperatures. These are known variously as winterizing temperature, minimum design metal temperature, low ambient temperature, low temperature, minimum winter temperature, minimum temperature, minimum design temperature, and minimum winterizing temperature to name a few. These temperatures have been developed from the various codes and, unfortunately, the names are sometimes used interchangeably with each other. Therefore, exercise caution when using these names.

This section defines the various low temperatures used in winterizing and defines whether the Customer or Inflection Point Engineering sets the temperature levels to be used.

4.1 Winterizing Temperature

The extreme case of the actual lowest recorded temperature is not normally selected as a design basis. In general, the winterizing temperature is the minimum temperature prevailing after rejection of a percentage of the lowest hourly temperature recordings in the coldest month or a percentage of the daily minimum temperature recordings for a year. Recordings are normally based on a period of years and not those of a single year. The percentage rejected is usually from 1 to 5 percent.

The "Winterizing Temperature" is shown in Section 4.1 of the BEDQ and is supplied by the Customer. See Attachment 1 Basic Engineering Design Questionnaire Section 4 for a copy of the BEDQ page containing Section 4.1.

4.2 Minimum Design Metal Temperature (MDMT)

"Minimum Design Metal Temperature" is defined by American Society for Mechanical Engineers (ASME) Code Section VIII, Division 1 and a calculation procedure was established by Inflection Point Engineering. See Procedure to determine the limiting lower design temperature of vessels, exchangers and pumps. The definition of this temperature is not limited to ambient conditions, since process operation can result in lower temperatures.

4.3 Low Ambient Temperature

Inflection Point Engineering defines the “Low Ambient Temperature” in the BEDQ as the lowest mean atmospheric temperature for a 24 hour period. The low ambient temperature is used as an input in the determination of the MDMT. The MDMT will usually be set equal to the low ambient temperature. However, exceptions include cases of auto-refrigeration and very cold process conditions.

The low ambient temperature is not used for purposes other than determining the MDMT, except in the event that the Customer does not supply the low temperature information for instrumentation design. In that case, the low ambient temperature is used as the default.

The “Low Ambient Temperature” is shown in Section 4.2 of the BEDQ and is supplied by the Customer. See Attachment 1 Basic Engineering Design Questionnaire Section 4 for a copy of the BEDQ page containing Section 4.2.

4.4 Objective Temperature

Use heat tracing to ensure that piping and equipment and their contents do not fall below a certain minimum temperature. For any heat tracing application, refer to this minimum temperature as the "Objective Temperature" of the piping or equipment which is set by Inflection Point Engineering.

For example, the design of a heat tracer for a section of piping is based on the tracer replacing the heat that is lost from the piping to the atmosphere when the piping is at the objective temperature and the atmosphere is at the winterizing temperature for the location involved and with an appropriate wind speed assumed. Refer to Inflection Point Engineering Standard Specifications and, .

5. Conditions Requiring Winterizing and Heat Tracing

Winterize and heat trace piping and equipment if any of the following conditions apply. Typically, do not winterize and heat trace piping and equipment if there is normally flow through them. There can be multiple exceptions, for example the continuous blowdown line on a steam generator (since flow through line may not be sufficient to keep it warm). Piping and equipment in intermittent service and dead legs (such as drains, vents, instruments, PRV’s, etc) on piping and equipment in normal service should typically be winterized and heat traced.

5.1 Freezing Point above Winterizing Temperature

Examples are pure compounds such as water, benzene, paraxylene, and cyclohexane and chemical solutions such as Sulfolane solvent, NaOH, KOH, MEA, and DEA (see Table 1).

5.2 Pour Point

Heavy hydrocarbon mixtures will stop flowing when the temperature is too low. Winterize and heat trace if the winterizing temperature is less than 25°F (14°C) above the pour point. For example, winterize and heat trace if the pour point is 20°F and the winterizing temperature is 44°F.

5.3 High Viscosity

High viscosity causes flow to be restricted or nonexistent with the normal differential pressure available. In the case of firing some fuel oils, the temperature must be maintained high enough to keep viscosity low enough for good atomization.

5.4 Vapor at its Dewpoint (if a problem)

Sometimes when a vapor exists at or near its water or hydrocarbon dewpoint, it is necessary to winterize and heat trace to avoid condensation if condensed liquid could cause problems. An example is a reciprocating compressor suction line.

5.5 Condensation, Hydrate or Ice Formation; Phase Separation

Cooling experienced by expanding gas may cause condensation, hydrate, or ice formation. Consider winterizing and heat tracing where phase separation, condensation, deposition of crystals, or hydrate formation may occur.

Where the conditions for freezing may only exist under certain special circumstances, the use of methanol injection may be acceptable and might avoid tracing and/or insulation.

Also, consult the appropriate Technology Specialist whenever there is a presence of any of the following:

H2O:H2S:Hydrocarbon together

NH4Cl

NH4SH

5.6 External Ice Formation

In some cases, process cooling inside of the process equipment or pipe (due to expansion of gas, etc) can cause the pipe temperature to drop low enough such that ice can form on the atmospheric side of the equipment. This ice can jam operation of control valves, etc. Consider winterizing and heat tracing to prevent this ice formation on the outside of the process equipment.

6. Design Considerations

6.1 Who Decides What the Low Ambient and Winterizing Temperatures Should Be?

Inflection Point Engineering is generally not involved in establishing winterizing or low ambient temperature data in our normal engineering scope. This is usually decided by the Customer and transmitted to Inflection Point Engineering through the medium of the BEDQ.

Question the Customer if a winterizing temperature of 32F (0C) is transmitted in the BEDQ. Establish with the Customer if water freezing is a problem and depending on the answer, revise the winterizing temperature to 31F (-1C) or 33F (1C). If, after discussions with the Customer, the winterizing temperature remains at 32F (0C), then provide protection for water freezing.

6.2 Minimize Heat Tracing

Design piping and equipment so that heat tracing is not required, or may be minimized when economical and feasible. An example is placement of block valves which minimize dead-end volumes.

6.3 Drain Equipment

Design piping and equipment containing liquids that will solidify or congeal during periods of non-operation to be drained, flushed, blown, steamed out, or cleaned, even if heat tracing is provided.

6.4 Emergency Showers

Winterize and heat trace emergency showers installed outdoors where freezing conditions may occur.

6.5 Special Attention

Give special attention to the following areas to determine if winterizing and heat tracing is required during start-up, shutdown, or normal operation. (Consider all the conditions listed in Section 5.)

All piping and equipment in water service including consideration of when intermittent or minimum flow will not maintain the temperature above freezing.

Water seals

Pressure relief valves: (Heat trace the relief valve, the relief valve inlet piping, and the relief valve tailpipe for freeze protection. Pilot operated relief valves, including the pressure pickup line and the pilot valve (which contains plastic/elastomeric seats and seals) shall be electrically heat traced. Apply water freeze protection in systems that have a free water phase present, or where a free water phase could exist if the fluid were cooled to winterizing temperature.)

Instrument impulse lines, level instruments and orifice taps

Auto-refrigeration at control, drain, and pressure relief valves

Piping that may be wet internally during start-up, upsets, or dryout operations. Inflection Point Engineering does not normally provide heat tracing protection for special operations such as regeneration or dryout and a note to this affect appears on the P&ID legend. A typical note is "Note: Piping and equipment have not been checked for winterizing during dryout or regeneration."

Low points and dead-ended pipes or legs

Drains (and traps) on piping, pumps, compressed air systems and fuel gas knockout pots

Lube and seal oil systems

Fuel oil tanks and piping

Diesel driven equipment, particularly firewater pumps and generators

Sample points

Concentrated acid and alkali solutions. To prevent overheating of carbon steel and consequent risk of embrittlement in this environment, Inflection Point Engineering specifies WISI (Winterize, Insulate, Steam trace, Insulate) steam heat tracing. See Standard Specification 1-14, "Steam Heat Tracing" for additional information on WISI-type heat tracing.

Since many of the winterizing and heat tracing issues may not be addressed until the process unit is in detailed design and construction, the Inflection Point Engineering P&ID carries the following note "This P and I Diagram is diagrammatic only. Design of pipe lines must be investigated for venting of gas or vapor pockets in piping and equipment, low points in piping, pumps and equipment for freezing and draining, and accessibility of all valves, flanges, instruments including thermocouples, etc."

6.6 Electrical Heat Tracing

Inflection Point Engineering specifies electrical heat tracing for certain instruments and pilot operated relief valves so that temperatures may be closely controlled. See Section 8.

7. Selection of Objective Temperature

Use the following table to set the objective temperature when a condition requiring winterizing and heat tracing is identified. Use the highest objective temperature identified.

Objective Temperature Selection Guidelines

Condition Identified	Specific Equipment	Objective Temperature
Freezing Point	All equipment	5 to 10°F (3 to 6°C) above freezing point. See Table 1.
Pour Point	All equipment	25°F (14°C) above the pour point.
High Viscosity	Centrifugal pumps <200 gpm	The temperature so that the viscosity is <500 SSU (110 cSt)
	Centrifugal pumps >200 gpm	The temperature so that the viscosity is <2000 SSU (440 cSt)
	Proportioning pumps	The temperature so that the viscosity is <6000 SSU(<1320 cSt)
	Level instruments including connecting piping
	Control valve assemblies
	Impulse lines to flow differential and pressure transmitters; differential level instruments	The temperature so that the viscosity is <5000 SSU (<1100 cSt) but see Section 8 for details
	Fuel oil supply lines to burners *	The temperature so that the viscosity is 100 SSU (20 cSt)
Dewpoint or Condensation	Gas to reciprocating compressor	The "equilibrium" receiver temperature (normal operating temperature)
	Fuel gas to heaters*	Per IPE-TM-200-02
	Flow differential and pressure transmitters in gas service	Heat tracing not normally required - free drainage required. Exceptions occur for condensable vapors and steam
Hydrate or Ice Formation	All equipment	Treat as freezing, subject to comments in Section 5.5.
Phase Separation	All equipment

*Refer to ProcedureSections 5.3 and 12.

8. Special Heat Tracing Requirements for Some Instruments

Inflection Point Engineering specifies electrical heat tracing for pilot operated relief valves, pressure and differential pressure transmitters in liquid service, and for displacement type level instruments and gauge glasses. See “Instructions for the Use of Inflection Point Engineering Design Specifications” shown in Attachment 2 Project Specification 000, Section 3 and Standard Specification .

The type of equipment specified for pressure and differential pressure transmitters depends on the objective temperature required by the process fluid. The objective temperature is dictated by the pour point or viscosity requirements for the process fluid being measured. The following table and Attachment 3 Flowchart for Instrument Impulse Piping Objective Temperature show the type of equipment specified for different objective temperatures of the instrument impulse piping.

Objective Temperature Required for Instrument Impulse Piping to obtain a Viscosity of <5000 SSU (<1100 cSt)	Objective Temperature Required for Instrument Impulse Piping to obtain a Viscosity of <5000 SSU (<1100 cSt)	Equipment Specified	Objective Temperature for Instruments
F	C
> 150	> 66	Wafer seal element/capillary diaphragm transmitter is used and pressure gauge has diaphragm seal	Impulse piping up to wafer seal element / diaphragm seal: Same objective temperature as required for impulse piping Capillary tubes and transmitter / pressure gauge: Usually not traced *
≤ 150	≤ 66	Conventional transmitter and pressure gauge is used	Same objective temperature as required for impulse piping

* Usually not traced unless the process fluid temperature is greater than 400°F (204°C), then trace the capillary tubes and transmitter / pressure gauge for an objective temperature of 150°F (66°C). Heat tracing is required because the high temperature [up to 600°F (315°C)] fill fluid in the capillary tubes / pressure gauge must be maintained above 60°F (15°C) to provide acceptable dynamic transmitter performance.

9. Showing Objective Temperature on the P&ID

The P&ID “Legend and Instrument Identification”, in the section titled "Miscellaneous Designations", shows the following statement: "Heat trace and insulate to maintain temperature as indicated in degrees Fahrenheit or Centigrade". Add the objective temperature alongside each item of equipment, piping and instrumentation on the P&ID, as appropriate.

Table 1 Freeze Points and Recommended Heat Tracing Objective Temperatures For Pure Compounds, Solutions, Inhibitors and Chemicals

Material	Material	Material	Freeze Point	Freeze Point	Objective Temperature	Objective Temperature
			F	C	F	C
Water	Water	Water	32	0	40	5
Benzene	Benzene	Benzene	42	5	50	10
Cyclohexane	Cyclohexane	Cyclohexane	44	6	50	10
Paraxylene	Paraxylene	Paraxylene	56	13	65	18
Sulfolane	Sulfolane	Sulfolane	82	28	90	32
Orthoxylene	Orthoxylene	Orthoxylene	-13	-25	-5	-20
	Be	wt%
NaOH*	5	3	28	-2	40	5
	10	7	20	-7	35	2
	20	14	2	-17	35	2
	25	19	-18	-28	35	2
	35	29	32	0	40	5
	43	39	60	16	70	21
	50	50	53	12	70	21
KOH	KOH	10	18	-8	35	2
		5	26	-3
MEA	MEA	20	15	-9	32	0
		15	22	-6
DEA	DEA	25	20	-7
		20	22	-6	35	2
		15	26	-3
DEG	DEG	DEG	16	-9
TEG	TEG	TEG	20	-7	32	10
TTEG	TTEG	TTEG	22	-6
UNICOR LHS	UNICOR LHS	UNICOR LHS	-30	-34	35**	2**
CCl4	CCl4	CCl4	-9	-24	0	-18
1,1,1-TCE	1,1,1-TCE	1,1,1-TCE	-27	-33	-17	-27

* Freeze point of NaOH will vary with concentration. See freeze point curve for exact freeze point. Minimum NaOH heat tracing objective temperature is 35ºF (2ºC).

** Set by viscosity

Attachment 1 Basic Engineering Design Questionnaire Section 4

Attachment 2 Project Specification 000, Section 3

3. Winterizing

Protection of process lines and associated equipment against atmospheric temperatures which would cause congealing or freezing of contents, interfere with operation, or cause damage to equipment is shown on the P&I Diagram(s).

Winterizing shown on the P&I Diagram(s) is based on the winterizing temperature indicated in the BEDQ, Section 4.1, “Winterizing Temperature”.

Electrical heat tracing shall be used for winterizing of:

1. Pressure and differential transmitters and their impulse lines.

2. Displacement type level instruments and gauge glasses, including the connecting piping.

3. Pilot operated relief valves including the pilot valve and its pressure pickup line.

Steam heat tracing shall be used for winterizing of lines and equipment labeled as "WISI" on the P&I

Diagram(s).

Either electrical or steam heat tracing may be used for all other winterizing applications shown on the P&I Diagram(s).

The following Inflection Point Engineering Standard Specifications shall be followed:

1-11 Winterizing

1-14 Steam Heat Tracing

7-15 Electrical Heat Tracing

Attachment 3 Flowchart for Instrument Impulse Piping Objective Temperature

IPE-TM-100-05

Winterizing Heat Tracing

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