mechanical - tube heat exchangers

REGLE PARTICULIERE / Job Specification

Activité - Unité Code Matériel N° ordre Rév.

RP 5293D001 0610 002 2

XXXXX ONSHORE GAS DEVELOPMENT PROJECT - PHASE II - PROJECT No. 1219

DESIGN GENERAL SPECIFICATION FOR SHELL & TUBE HEAT EXCHANGER DESIGN CRITERIA

Page

B

TABLE OF CONTENTS

1.0 GENERAL....................................................................................................................................................................

1.1 INTRODUCTION..........................................................................................................................................................1.2 PURPOSE......................................................................................................................................................................1.3 DEFINITIONS...............................................................................................................................................................1.4 EXCEPTIONS................................................................................................................................................................

2.0 CODES AND STANDARDS.........................................................................................................................................

3.0 REFERENCE DOCUMENTS......................................................................................................................................

4.0 DOCUMENT PRECEDENCE.....................................................................................................................................

5.0 SPECIFICATION DEVIATION/CONCESSION CONTROL....................................................................................

6.0 DESIGN.........................................................................................................................................................................

6.1 GENERAL REQUIREMENTS.......................................................................................................................................6.2 TECHNICAL REQUIREMENTS...................................................................................................................................

7.0 MATERIALS................................................................................................................................................................

8.0 FABRICATION............................................................................................................................................................

9.0 TESTING......................................................................................................................................................................



RP 5293D001 0610 002 2



Page

1

1.0 GENERAL

1.1 INTRODUCTION

This Specification establishes the criteria for the thermal design of standard TEMA type Shell and Tube Heat Exchangers for the PROJECT. It also defines the minimum process and mechanical data required for thermal and hydraulic design and completion of Heat Exchanger Data Sheets (hereinafter referred to as “Data Sheets).

1.2 PURPOSE

The purpose of this specification is to ensure consistency in selection and design of TEMA type shell and tube heat exchangers for the XXXXX Onshore Gas Development Project Phase II - Project N° 1219.

1.3 DEFINITIONS

For the purpose of the specification, the following, definitions shall apply.

1.3.1 COMPANY - The XXXXX National Oil COMPANY (XXXXX).

1.3.2 CONCESSION REQUEST - A deviation requested by the CONTRACTOR or VENDOR, usually after receiving the contract package or purchase order. Often, it refers to an authorization to use, repair, recondition, reclaim, or release materials, components or equipment already in progress or completely manufactured but does not meet or comply with XXXXX requirements. A CONCESSION REQUEST is subject to PMT approval.

1.3.3 CONTRACTOR - The party which carries out all or part of the design, engineering, procurement, construction, commissioning or management of the PROJECT.

1.3.4 MANUFACTURER/VENDOR - The party which MANUFACTURERS and/or supplies equipment, technical documents/drawings and services to perform the duties specified by XXXXX/CONTRACTOR.

1.3.5 PROJECT - XXXXX OGD PROJECT 1219 - PHASE II.

1.3.6 PROJECT MANAGEMENT TEAM (PMT) - The COMPANY authorized party responsible for the overall day-to-day execution of the PROJECT. The PMT is to serve as the liaison between the COMPANY and the CONTRACTOR(s) on the PROJECT.

1.3.7 SHALL - Indicates a mandatory requirement.



RP 5293D001 0610 002 2



Page

2

1.3.8 SUBCONTRACTOR - The party(s) which carry(s) out all or part of the design, procurement, installation and testing of the System(s) as specified by the CONTRACTOR/VENDOR.

1.4 EXCEPTIONS

This specification does not apply to design of Double Pipe Heat Exchangers, Plate Heat Exchangers, Water Cooled Surface Condensers, and Brazed Aluminium Fin Heat Exchangers. For other special applications only part of this specification may be relevant, subject to mutual agreement between VENDOR/MANUFACTURER and COMPANY/CONTRACTOR.

2.0 CODES AND STANDARDS

Tubular Exchanger Manufacturers Association (TEMA) Standards, Seventh Edition, 1988 including 1990 Errata or the latest edition in force at the time of contract award shall apply.

3.0 REFERENCE DOCUMENTS

This section is not applicable to this Specification.

4.0 DOCUMENT PRECEDENCE

It shall be the VENDOR responsibility to be, or to become, knowledgeable of the requirements of the referenced Codes and Standards.

The VENDOR shall notify the CONTRACTOR of any apparent conflict between this specification, the related data sheets, the Codes and Standards and any other specifications noted herein. Resolution and/or interpretation precedence shall be obtained from the CONTRACTOR in writing before proceeding with the design/manufacture.

In case of conflict, the order of precedence shall be:

a. Equipment Data Sheet(s)

b. Equipment Narrative Specification or Design criteria.

c. PROJECT Specifications and Standards

d. Industry Codes and Standards



RP 5293D001 0610 002 2



Page

3

5.0 SPECIFICATION DEVIATION/CONCESSION CONTROL

Any technical deviations to the Purchase Order and its attachments including, but not limited to, the Data Sheets and Narrative Specifications shall be sought by the VENDOR only through CONCESSION REQUEST format. CONCESSION REQUESTS require CONTRACTOR’S and COMPANY’S review/approval, prior to the proposed technical changes being implemented. Technical changes implemented prior to COMPANY approval are subject to rejection.

6.0 DESIGN

6.1 GENERAL REQUIREMENTS

6.1.1 Definitions

Clean Service shall satisfy the following conditions:

e. Fouling resistance less than or equal to 0.00041 m2hr°C/kcal (0.002 ft2 hr °F/Btu).

f. Where chemical cleaning is proven effective for fouling factors exceeding 0.00041 m2hr°C/kcal, such cases shall be identified and approved by COMPANY. Once approved, they shall be treated as Clean Service.

Fouling Service shall include all services not otherwise defined as “clean service,” or where mechanical cleaning is required.

6.1.2 Process Data

In addition to heat duty, fluid identity, flow rates, design pressures and temperatures, operating pressures and temperatures, allowable pressure drops, material of construction and exchanger type and setting, the process data shall include but not be limited to the following:

6.1.2.1 Sensible Heat Transfer Service

g. Vapor and Gas

h. Density, thermal conductivity, specific heat and viscosity at two reference temperatures, molecular weight and hydrogen partial pressure.

i. Liquid

· Density, thermal conductivity, specific heat and viscosity at two reference temperatures. For liquid streams having a high viscosity, a third viscosity data point at an intermediate temperature or viscosity/temperature correlation is desirable, except that when the viscous liquid is being cooled, the third data point should be at the average temperature of the opposing stream.



RP 5293D001 0610 002 2



Page

4

· Physical properties of hydrocarbon streams shall be weighted to include the effect of miscible water, and shall be so specified.

· Immiscible or free water shall be shown on the Data Sheet. Fluid properties shall not be weighted to include immiscible water.

6.1.2.2 Condensing Service

j. Physical property requirements shall be the same as for sensible heat transfer plus the bubble point, dew point, latent heat, quantity and molecular weight of noncondensible gas and quantity of steam when present. Vapor physical properties shall be weighted for the entire vapor phase mixture. For cases where H2 content is more than 10 mol percent, vapor mixture physical properties shall be given under three referenced temperatures. Latent heat for a steam/hydrocarbon mixture shall be for the hydrocarbon only.

k. Data sheets shall state if condensation is linear.

l. For non-linear heat release services, a plot with duty, weight percent vapor and molecular weight versus temperature shall be provided.

m. When fluid entering exchanger is a vapor mixture at its dew point temperature, liquid properties shall also be given at that temperature unless sensible heat is 10 percent or less of total duty.

6.1.2.3 Boiling Service

n. Physical property requirements shall be the same as for sensible heat transfer plus liquid surface tension, mixture bubble point and dew point, critical pressure and temperature and latent heat.

o. The Process Engineer shall provide tables or curves showing vapor temperature and fraction vaporized at two constant reference pressures between bubble point and dew point, with three additional points between. The three additional points must be close to the operating range. For pure components or in cases with very narrow boiling ranges only vapor pressures at two temperatures need be provided.

p. For non-linear heat release services, a plot with duty, molecular weight and weight percent vapor versus temperature shall be provided.

q. For kettle reboilers, the required entrainment ratio (kg liq/kg vapor) shall be provided, including steam purity for steam generators.

r. For thermosyphon reboilers complete piping geometry between the fractionating column and the reboiler must be analyzed, together with the available static head.



RP 5293D001 0610 002 2



Page

5

6.1.2.4 Corrosion Allowance

s. For all exchanger parts, except tubes, the materials of construction and corrosion allowance shall be selected to give exchangers a design service life of 30 years being in accordance with PROJECT Specifications. Corrosion allowance shall be specified on the Data Sheets.

t. Tubes shall have a design life of 100000 hours and where necessary to achieve this, corrosion allowance for tubes in high pressure service shall be specified.

u. Corrosion allowance for nozzles and manholes shall be equal to that specified for shell/head. Standard corrosion allowance for carbon and low alloy steels shall be 3 mm. Where a larger corrosion allowance is required this will be shown on the data sheets.

6.1.2.5 Fouling

Fouling factors and cleaning requirements shall be specified on the Data Sheets.

6.1.2.6 Nozzle Sizes

Where practical, the exchanger nozzles shall be designed to match the line sizes provided that exchanger thermal, vibration and hydraulic requirements are met, and that TEMA entrance and exit velocity criteria are satisfied.

6.1.2.7 Excess Heat Transfer Surface

Any requirements for excess surface must be fully explained on the data sheet, with instruction on effect on flow, temperatures and pressure drops if these are to differ from those listed on the data sheets. It is insufficient to add notes such as “provide 10 percent excess surface.”

6.1.2.8 Design Temperature and Pressure

v. All parts of the tube bundle including floating head shall be designed for either full tube side internal pressure or full shell side external pressure, whichever condition is controlling. Differential pressure shall not be used as design basis unless specified.

w. In selecting design temperatures for multiple exchangers in series, consideration shall be given to the maximum or minimum temperature, on each side of each exchanger, that results from either fouled or clean operation.

x. The differential between the inlet and outlet operating temperatures of a shell side fluid should not exceed 200°C (400°F) per shell.

y. The differential between the inlet and outlet operating temperatures of channels of multipass exchangers should not exceed 120°C (250°F) per exchanger.



RP 5293D001 0610 002 2



Page

6

z. For the determination of the design pressure on the low pressure side, the greater of the initial design pressure on the low pressure side or 2/3 of the design pressure on the high pressure side shall be taken. However, if it is economic to maintain the initial design pressure on the low pressure side by installing a relief device, this may be considered. The size of the relief device shall be determined based on a possible tube rupture. The size of the leak shall be taken twice the internal cross-sectional area of one tube.

aa. For heat exchangers in series, individual shells of a unit may have different design temperatures for economy in material selection. Where this applies, measures shall be taken to prevent incorrect line-up of shells within the unit.

bb. The effect of the temperature profile over a thick wall tubesheet not being linear shall be taken into account because this may have a large consequence on the “mean metal temperature” as well as on the temperature gradient and stresses within the tubesheet.

cc. Minimum design pressure shall be Identified on data sheets.

dd. Both, Design Temperature (DT) and Minimum Design Metal Temperature (MDMT) shall be identified on Data Sheets.

6.1.2.9 Allowable Pressure Drop

Allowable pressure drop shown on the Data Sheet shall be for clean service.

6.1.3 Mechanical Data

The complete Data Sheets shall include the following information, as a minimum:

ee. Process data (including heat release curves, when applicable).

ff. Parameters defining exchanger’s thermal performance (i.e. heat transfer coefficients, calculated pressure drops, Mean Temperature Difference, etc.).

gg. Definition of exchanger’s type and orientation.

hh. Identification of any special design considerations.

ii. Outline drawing, defining overall dimensions, required maintenance clearances, locations of vents, drains and any other non-process connections, process nozzles size, rating, location and projection, saddles location and projections, location and sizing of the anchor bolts, flow direction.

jj. Definition of internals, like baffle spacing, or internal expansion joints.

kk. Tube layout including as a minimum: number of tubes, tube diameter, outer tube limit (OTL), baffle cut, baffle orientation, sealing and sliding strips, tie rod



RP 5293D001 0610 002 2



Page

7

location and size, definition of impingement protection (if required), schematic identification of the shellside nozzle size.



RP 5293D001 0610 002 2



Page

8

ll. Identification of materials and corrosion allowances.

mm.Identification of special services and NDE requirements.

nn. Identification of PMI requirements.

6.2 TECHNICAL REQUIREMENTS

6.2.1 TEMA Class Selection

All shell and tube heat exchangers for this PROJ Launch Microsoft Office Outlook.lnk ECT shall be in accordance with TEMA class R.

6.2.2 Exchanger Type Selection

6.2.2.1 Front/Rear Head Selection

oo. In general, bonnet Type B should be used for the front end stationary head. For water-cooled exchangers where frequent tube side cleaning is anticipated and the tube side design pressure is less than 10 bar g, the front end stationary head shall be Type A.

pp. Rear end head Type M should be used for fixed tubesheet designs. However, for heat exchangers with a Type A front end stationary head and an odd number of tube passes Type L shall be selected.

qq. Rear end head Type S should be used for floating head type heat exchangers with a nominal shell diameter of more than DN 250. Alternative construction would need to be considered for diameters up to DN 250. Rear end head Type T shall be used for a kettle type heat exchanger with floating head.

rr. High pressure or other design requirements may justify deviation from the guidelines shown.

6.2.2.2 Use of Fixed Tubesheet (non removable bundle) Exchangers

ss. Use of fixed tubesheet exchangers requires prior approval by the COMPANY.

tt. Nonremovable bundle exchangers may be used in clean shell side service where a shell expansion joint is not required. The use of shell side expansion joints is not permitted.

uu. The differential expansion between shell and tubes of a fixed tubesheet exchanger shall be based on the controlling metal temperatures, either clean or one side fouled.



RP 5293D001 0610 002 2



Page

9

vv. The maximum controlling differential temperature between the tube and shell side during operation, start-up, shutdown or steamout shall be stated on the data sheet and used to determine the requirement for an expansion joint and tubesheet thickness on a fixed tubesheet heat exchanger. If design consideration result in expansion joint being required, removable bundle type shall be selected.

6.2.2.3 Use of U-Tube Bundles

U-tube bundles shall be used only for the Clean Service on the tubeside as defined in para 6.1.1. Other design considerations may govern, but require prior approval by the COMPANY.

6.2.2.4 Shell Selection

The single-pass shell, Type E, shall be selected for general duties, except as indicated below:

ww.Where the shell side pressure drop is a restricting factor, the divided flow shell Type J or cross-flow shell Type X or double-split flow shell Type H, should be considered.

xx. For horizontal shell side thermosyphon reboilers, Type G, J, X, or Type H should be selected.

yy. The kettle type shell, Type K, should be selected for boiling where almost 100% vaporization (0-5% entrainment) or where a phase separation is required.

zz. The use of TEMA Type F shells with removable bundles is discouraged unless there are considerable economic savings or design advantages. Limit shell side pressure drop to 0.48 bar (7.0 psi) per shell and temperature differential between shell inlet and shell outlet to 140°C (250°F).

6.2.2.5 Horizontal and Vertical Exchangers

aaa.Heat exchangers should be of the horizontal type; however, for process requirements or where cleaning and other maintenance will be infrequent or space requirements make it more attractive, the vertical arrangement may be considered.

bbb.For thermosyphon reboilers, vertical or horizontal orientation may be used. The choice of orientation shall take into consideration the total installed cost, maintenance costs, fouling characteristics of both fluids and avoidance of vibration problems.

ccc.When horizontal arrangements are preferred, the stacking of exchangers should be considered to conserve space in the structure. Preferred stacking should be 2 (two) shells high.



RP 5293D001 0610 002 2



Page

10

6.2.3 Tube Bundle

6.2.3.1 Maximum Size

ddd.Maximum sizes shall be as shown below. Larger sizes may be considered to realize economic or design advantages. Larger sizes must be approved by the COMPANY

· The maximum straight length tubes shall be 7315 mm (24 feet), except that for fixed tube sheet bundles a maximum length of 18,300 mm (60 ft) may be considered in order to obtain sufficient velocity of flow on the tube side for clean service applications, subject to COMPANY approval on a case by case basis.

· The maximum bundle diameter for removable bundle exchanges shall be 1,524 mm (60 in). The maximum removable bundle weight shall be 18,140 kg (40,000 lb). The ratio of tube length to bundle outer diameter shall be less than 10:1.

eee.Standard straight lengths for tubes shall be as follows:

Millimeters 2440 3050 3660 4880 6100 7315

(Feet) (8) (10) (12) (16) (20) (24)

fff. The preferred tube lengths are 3050, 3660, 4880 and 6100 mm

ggg.Selection of different tube lengths then above for U-tubes may be considered when economically justified, subject to company approval.

hhh.The maximum tube length for vertical thermosyphon reboilers shall be 6100 mm (20 ft).

6.2.3.2 Tube Diameters and Gauges

The following table specifies bare tube diameters and minimum permissible gauges (BWG).

TUBE OD CARBON STEEL AND LOW ALLOYS

HIGH ALLOYS

15.88 mm*

(0.625) in

(MIN. WALL)

2.11 mm

(0.083) in

(MIN. WALL)

1.65 mm

(0.065) in

19.05.mm

(0.75) in

2.11 mm

(0.083) in

1.65 mm

(0.065) in

25.4 mm

(1) in

2.77 mm

(0.109) in

2.41 mm

(0.095) in

31.75 mm** 2.77 mm 2.41 mm



RP 5293D001 0610 002 2



Page

11

(1.25) in (0.109) in (0.095) in



RP 5293D001 0610 002 2



Page

12

* Allowed only for clean gas condensing in tubes. Requires prior approval by COMPANY.

** Use of 31.75 mm OD tubes requires prior approval by COMPANY.

6.2.3.3 Tube Diameter, Pitch and Layout

The following table defines criteria for selection of tube diameter, pitch and layout:

SHELL SIDE SERVICE

TUBE SIDE FOULING

m2hr°C/k cal(ft2hr°F/Btu)

MIN. TUBE O.D.

mm ( in.)

PITCH, mm (in.)

and layout

Clean* Up to and including 0.0006 (0.003)

19.05 (0.75) 25.4 (1.0) 30°

Clean* Over 0.0006 (0.003)

25.4 (1) 31.75 (1.25) 30°

Fouling* Up to and including 0.0006 (0.003)

19.05 (0.75) 25.4 (1) 90°/45°

Fouling* Over 0.0006 (0.003)

25.4 (1) 31.75 (1.25) 90°/45°

* As defined in para 6.1.1

Exceptions to the above table are as follows:

iii. The pitch and layout guidelines shown above are the minimum starting points for economic design. Larger pitch or different layout patterns may be required to satisfy pressure drop or boiling flux requirements.

jjj. Tube pitch for heavy wall tubes shall not be less than the recommended values in TEMA Table R-7.42.

kkk.Rotated square layouts (45°) are preferable for Laminar Flow. In turbulent flow, especially for pressure drop-limited cases, square layout (90°) is preferred.

6.2.3.4 Baffles and Support Plates

lll. Permissible types of transverse baffles are segmental, double segmental and the segmental type having no tubes in the window area.



RP 5293D001 0610 002 2



Page

13

mmm.Horizontal cut baffles are preferred for most services, including two phase flow with vapor generation. Vertical cut should be used for condensing vapors, liquids containing suspended solids, and in TEMA F, G and H shells. Regardless of baffle orientation, vaporizing flow in the shellside should be designed to be in shear flow rather than gravity flow.

nnn.Baffle cut perpendicular to nozzle centerline (normally horizontal cut) is preferred for single phase fluids. Where shellside inlet nozzle has 180 ° rotation from shellside outlet nozzle, the number of shellside crosspasses must be odd for segmental baffles.

ooo.The minimum baffle cut for segment baffles shall be 15 percent of the shell inside diameter.

ppp.All U-tube bundles shall have full support plate at u-bend. The full support plate shall be trimmed to the extent defined by the baffles outline (on top and bottom) but covering the full tube layout.

6.2.3.5 Bundle Rotation

Where possible, without decreasing the thermal performance of exchanger, the carbon steel U-tube bundles shall be designed to allow their operation after being placed back into exchanger, following 180° rotation around their longitudinal axis.

6.2.3.6 Tubesheet

All removable bundles used with B type front head shall have their stationary tubesheets extended to be equal to shell flange outside diameter. Tubesheet thickness must be sufficient to eliminate a need for test rings.

Removable bundles used with A type front head do not need to have full diameter tubesheets.

6.2.3.7 Maximum Unsupported Tube Length

The maximum unsupported tube span shall not be more than 0.8 times the values shown on TEMA Table RCB-4.52.

6.2.3.8 Finned Tubes

Wolverine type S/T (or equal) low and medium height integral fin tubes are acceptable under the following conditions, but require COMPANY approval:

qqq.The shell side fouling resistance using low fin tubes does not exceed 0.0002 m2hr °C/kcal. Medium height fin tubes are to be used only in gas services with fouling not greater than 0.0002 m2 m °C/kcal.

· The shell side stream is boiling or in the turbulent regime.



RP 5293D001 0610 002 2



Page

14

· The shell side stream is a clean cooling/condensing service. The number of fins per meter shall not exceed 748 for liquid/condensing service and 1025 for gas service.

rrr. Their application is economically attractive. As a general guidelines, the heat transfer coefficients, when corrected for fouling, show the shell side controlling by a ratio of 2:1 or more for low fin tubes and 3:1 or more for medium high fin. To avoid fretting of the tubes in baffle/support plates, the baffle, support plates shall have a thickness in accordance with TEMA Table R-4.41; however, the minimum thickness shall not be less than 13 mm.

sss.High-finned tubing is not permitted.

ttt. Longitudinally-finned tubes are only allowed for double-pipe heat exchangers. This will normally be high-finned tubing.

6.2.3.9 U-Tube Bundle Bend Radius

Bends with radius R <1.5 times nominal tube OD are not permitted.

6.2.4 Water-Cooled Coolers

6.2.4.1 The following shall apply to water-cooled coolers:

Cooling water shall be placed on the tube side and should run upwards through the tubes in order to avoid gas build-up. The tube side velocity should be as specified in this specification. The tube side shall be maintained at an atmospheric over-pressure so that air cannot separate from/be sucked into the water.

6.2.4.2 Cooling Water Velocity

Tube side velocity for chilled water shall not exceed the maximum listed below and preferably should not be below the minimum.

uuu.Tube Material vvv.Velocity m/s (FPS)

www.Carbon and Low Alloy Steel

xxx.1.0 - 1.8

yyy.(3-6)

zzz.Austenitic Stainless Steel aaaa.2.0 - 4.5

bbbb.(6.5 - 13)

cccc.Titanium dddd.0.92 - 4.57

eeee.(3-15)

ffff. Inhibited Admiralty gggg.0.92 - 2.74

hhhh.(3-9)

iiii. 70-30 Cu-Ni jjjj. 1.0 - 3.0 kkkk.(3-10)

llll. 90-10 Cu-Ni mmmm.1.0 nnnn.(3.8)



RP 5293D001 0610 002 2



Page

15

- 2.5

oooo.Alum. Brass, Alum. Bronze pppp.1.0 - 2.1

qqqq.(3.7)

rrrr.Monel ssss.1.8 - 3.5

tttt. (6 - 11.5)

uuuu.Incoloy 825, Carpenter 20 CB3

vvvv.1.52 - 3.66

wwww.(5-12)



RP 5293D001 0610 002 2



Page

16

6.2.5 Tube/Shell Side Selection

In general, tube side/shell side selection shall be made to satisfy as many as possible of th following points, unless otherwise indicated on Data Sheets:

Service Shell Side Tube Side

Cooling Water X

Condensing Vapors (except steam)

X

Lower Allowable DP X

Larger Flow and Similar Properties

X

Higher Pressure Fluids X

Corrosive Fluids/Alloy Construction

X

*High Fouling Factors X

High Viscosity/Laminar Flow X

* If chemical cleaning can be utilized, the fouling fluid may be placed on the shell side.

6.2.6 Special Applications

6.2.6.1 Slurry Handling

Slurry services shall be routed through the tube side of the exchanger.

Minimum tube size shall be 25.4 mm (1 in.) OD at 2.77 mm (0.109 in.) (BWG) wall thickness.

Velocity limits for cycle oil containing catalyst fine shall be as listed below. The optimum velocity is 1.75 m/sec (5.75 ft/sec).

xxxx.Velocity m/s (FPS)

Maximum Minimum

Straight tube 21.3 (7.0) 1.14 (3.75)

U-tube 1.75 (5.75) 1.14 (3.75)

Straight tube construction is recommended.



RP 5293D001 0610 002 2



Page

17

Slurry flow shall be horizontal or downward.



RP 5293D001 0610 002 2



Page

18

6.2.6.2 HF Acid/Lethal Service

To minimize chances of acid leakage into the process area, exchanger design shall provide as few joint closures as practical.

6.2.6.3 Pulsating Flow on Shell Side

Maximum unsupported tube length for vapor or 2-phase flow shall be 914 mm (36 inches).

Design shall include adequate impingement protection plate or a distributor belt so that rV2 into a bundle shall not exceed 744 kg/(m.sec2) (500 lb/(ft.sec2)).

6.2.7 Kettle-Type Reboilers and Evaporators

The shell diameter depends on the required vapor escape area above the tube bundle. Vapor velocities shall nowhere exceed the maximum vapor velocity determined by the entrainment requirements.

These entrainment requirements shall be specified in Data Sheets. The entrainment coefficient shall be calculated per HTRI-RKH3 manual, page 3-28 and used in the RKH3 program to size the vapor space. Other methods may be used with COMPANY approval.

The design shall take into account that frothing is likely to occur above the liquid level. An allowance 125 mm shall be made for this frothing. The height of the escape area above the frothing allowance shall be at least 250 mm.

Minimum of two (2) vapor outlet nozzles shall be used for bundles longer than 4880 mm (16 ft).

The entry for vapor/liquid mixtures shall be above the boiling pool. Provision shall be made to separate the vapor phase from the liquid phase by using a deflector baffle, spider pipe or other suitable means.

A device recommended for distributing the liquid/vapor mixture above the froth bed is the spider pipe arrangement shown in Figure 1 below:

Figure 1. SPIDER PIPES



RP 5293D001 0610 002 2



Page

19

The requirements for spider pipes are as follows:

yyyy.Located at the position of lowest vapor generation

zzzz.The mixed vapor/liquid stream should direct downwards against the shell wall to promote separation of the liquid and vapor.

aaaaa.No holes in the direct path from the inlet nozzle

bbbbb.The velocity head in the inlet nozzle shall be 4000 kg/m/sec2 maximum

ccccc.The velocity head in the spider header shall be 1000 kg/m/sec2 maximum

ddddd.The velocity head in the holes shall be 4000 kg/m/sec2 maximum

If considered necessary, provision shall be made for cleaning the spider.

A vortex breaker shall be provided for the liquid outlet nozzles.

If the liquid level is to be maintained at a fixed height, a weir shall be installed between the boiling compartment and the rundown compartment to keep the bundle submerged. The top of the weir shall be at least 25 mm above the top of the bundle. Unless required by process considerations, drain holes are not permitted in this weir.

If the liquid level is to be controlled by instrumentation, a calming baffle shall be installed to prevent boiling turbulence from affecting the level instruments.

The liquid space shall be determined by the liquid hold-up requirements.

A distance of 50 mm minimum shall be maintained between the bottom of the bundle and the bottom inside diameter of the shell so as not to obstruct liquid re-circulation into the bundle.

6.2.8 Venting and Draining of Exchangers

All shell and tube exchangers, including vertical units, shall be provided with vents and drains allowing complete draining and venting of shell side and tube side of exchangers, after hydrotest “in-situ”.

Vertical fixed tubesheet exchangers shall have vent and drain passages drilled through the tubesheet to exit at the outside edge of the tubesheet to ensure complete venting and draining of the shell. Connections should preferably be 2” (DN50). This may be reduced to a minimum of 1” (DN25) in case of thin tubesheets.

For stacked exchangers of the same service, hydrotest “in-situ” can be performed in stacked position, but each shell shall be completely drainable and ventable.

Separate vents and drains on exchangers are not necessary if hydrotest “in-situ” and subsequent draining and venting of exchangers can be accomplished through piping connections or line breaks.



RP 5293D001 0610 002 2



Page

20

6.2.9 Design for Interchangeability

Design of shell and tube heat exchangers for the PROJECT shall target maximum interchangeability of complete units or components.

6.2.10 Shell Diameter

Up to nominal diameter of 500 mm (20 in) line pipe shall be used.

For shells rolled from plate, the nominal shell diameter is the shell inside diameter.

For shells rolled from plate, inside diameters should be changed in 10 mm increments during thermal design or sizing. This requirement can be deviated from in case of high pressure application and when it is economically justified.

6.2.11 Maximum Number of Tube Passes

The maximum number of tube passes shall be 16 for any given heat exchanger.

7.0 MATERIALS

Materials selection shall be indicated on the PROJECT equipment Data Sheets.

8.0 FABRICATION

PROJECT equipment Data Sheets shall indicate any special fabrication requirements.

9.0 TESTING

PROJECT equipment Data Sheets shall indicate any special testing requirements.

mechanical - tube heat exchangers

Documents