Pumps for Sodium Hydroxide Service

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Engineering Design Guide:
GBHE_EDG_MAC_1514
Pumps for Sodium
Hydroxide Service
Process Disclaimer
Information contained in this publication or as otherwise supplied to Users is
believed to be accurate and correct at time of going to press, and is given in
good faith, but it is for the User to satisfy itself of the suitability of the information
for its own particular purpose. GBHE gives no warranty as to the fitness of this
information for any particular purpose and any implied warranty or condition
(statutory or otherwise) is excluded except to the extent that exclusion is
prevented by law. GBHE accepts no liability resulting from reliance on this
information. Freedom under Patent, Copyright and Designs cannot be assumed.

Engineering Design Guide: Pumps for Sodium Hydroxide
Service
CONTENTS
1 SCOPE
2 PROPERTIES OF FLUID
2.1 General Properties of Sodium Hydroxide
2.2 Physical Properties of Sodium Hydroxide and its Solutions
2.3 Chemical Properties and uses of Sodium Hydroxide
2.4 Physiological effects of Sodium Hydroxide
2.5 Specifications of Commercial Caustic Soda Grades
3 CHOICE OF PUMP TYPE
3.1 Pump Duty
3.2 Pump Type
4 RECOMMENDED LINE DIAGRAMS
5 RECOMMENDED LAYOUT
6 CONSTRUCTION FEATURES
7 MATERIALS OF CONSTRUCTION
7.1 Nickel and Nickel Alloys
7.2 Austenitic Stainless Steel
7.3 Aluminium, Aluminium Alloys, etc.
7.4 Non-Metallic Materials

TABLES
1 PHYSICAL PROPERTIES (Solid Form)
2 PHYSICAL PROPERTIES (Solution Form)
3 CAUSTIC SODA GRADES
FIGURES
1.1 LINE DIAGRAM - HORIZONTAL GLANDED, GLANDLESS AND
VERTICAL IN-LINE PUMPS
1.2 LINE DIAGRAM - VERTICAL SPINDLE CANTILEVER PUMPS
1.3 LINE DIAGRAM - SELF PRIMING PUMPS
1.4 LINE DIAGRAM - RECIPROCATING PLUNGER METERING PUMPS
1.5 LINE DIAGRAM - POSITIVE DISPLACEMENT DIAPHRAGM
METERING PUMPS
1.6 WATER FLUSHING ARRANGEMENT FOR DOUBLE MECHANICAL
SEAL
1.7 WATER FLUSH (QUENCH) ARRANGEMENT FOR SINGLE HARD
FACED (CARBIDE) SEAL AND BACK-UP LIP SEAL
2 PHASE DIAGRAM OF NaOH-H2O
3 VISCOSITY OF AQUEOUS CAUSTIC SODA SOLUTIONS
4 VAPOR PRESSURE OF AQUEOUS CAUSTIC SODA SOLUTIONS
5 ENTHALPY CONCENTRATION FOR AQUEOUS CAUSTIC SODA
SOLUTIONS

6 SPECIFIC GRAVITY FOR AQUEOUS CAUSTIC SODA SOLUTIONS
7 DILUTION OF CAUSTIC SODA LIQUOR
8 THERMAL CONDUCTIVITY OF AQUEOUS CAUSTIC SODA
SOLUTIONS
9 SPECIFIC HEAT OF CAUSTIC SODA SOLUTIONS
10 BOILING POINTS OF STRONG CAUSTIC SODA SOLUTIONS
AT REDUCED PRESSURE
11 COMMENCEMENT OF FREEZING OF CAUSTIC SODA SOLUTIONS
(0 - 52% W/W)
12 TEMPERATURES ATTAINED ON DISSOLUTION OF ANHYDROUS
CAUSTIC SODA
13 HEAT OF SOLUTION FOR ANHYDROUS CAUSTIC SODA
14 SOLUBILITY OF SODIUM CHLORIDE IN CAUSTIC SODA SOLUTIONS
15 DENSITY - CONCENTRATION TABLES FOR CAUSTIC SODA
SOLUTIONS AT 600 F (15.5 0
C)
16 MATERIAL SELECTION CHART FOR CAUSTIC SODA HANDLING
DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE

1 SCOPE
This Engineering Design Guide provides guidance on the selection of
suitable pumps for pumping Sodium Hydroxide and its various aqueous
solutions.
2 PROPERTIES OF FLUID
2.1 General Properties of Sodium Hydroxide
Sodium hydroxide is commonly called caustic soda within industry. It is
generally handled in solution form at varying strengths from 6% to 100%
caustic soda. The physical properties of the solutions vary with the caustic
strength as shown in 2.2 which summarizes the properties for the most
common solution strengths.
The 100o
Twaddell (47% w/w) caustic soda liquor is the most common
solution as it is both easy and economical to distribute and in this form it is
an almost colorless liquid, being quite viscous and dense. It is miscible
with water in all proportions below this value and the commencement of
freezing varies dramatically with solution strength.
100% caustic soda is a solid at room temperature.
2.2 Physical Properties of Sodium Hydroxide and its Solutions
Chemical formula NaOH
Molecular weight 40
Melting Point 318o
C
Sodium hydroxide (100% w/w) has the following additional physical
properties:
(a) It is a white crystalline solid at ambient conditions.
(b) It is very soluble in water giving off a large amount of heat in the
process.
(c) It is deliquescent.

(d) It absorbs carbon dioxide from the air.
In solid form, the following physical properties apply:
TABLE 1: PHYSICAL PROPERTIES (Solid Form)
In solution form, the-following physical-properties apply:
TABLE 2: PHYSICAL PROPERTIES (Solution Form)

The following Figures apply:
Figure 2 Phase diagram of NaOH-H2O
Figure 3 Viscosity of Aqueous Caustic Soda Solutions
Figure 4 Vapor Pressure of Aqueous Caustic Soda Solutions
Figure 5 Enthalpy Concentration for Aqueous Caustic Soda
Solutions
Figure 6 Specific Gravity for Aqueous Caustic Soda Solutions
Figure 7 Dilution of Caustic Soda Liquor
Figure 8 Thermal Conductivity of Aqueous Caustic Soda
Solutions
Figure 9 Specific Heat of Caustic Soda Solutions
Figure 10 Boiling Points of Strong Caustic Soda Solutions at
Reduced Pressure
Figure 11 Commencement of Freezing of Caustic Soda Solutions (0 - 52%
W/W)
Figure 12 Temperatures Attained on Dissolution of Anhydrous
Caustic Soda
Figure 13 Heat of Solution for Anhydrous Caustic .Soda
Figure 14 Solubility of Sodium Chloride in Caustic Soda
Solutions
Figure 15 Density - Concentration Tables for Caustic Soda
Solutions at 60° F (15.5° C)
Figure 16 Material Selection Chart for Caustic Soda Handling.

2.3 Chemical Properties and uses of Sodium Hydroxide
Sodium hydroxide is highly corrosive and one of the strongest alkalis in
commercial use. It is a very stable compound and cannot be converted
into the oxide by heating. Aqueous sodium hydroxide attacks glass, the
silica being dissolved as sodium silicate. It also dissolves metallic boron,
silicon, aluminium, tin and zinc, liberating hydrogen and forming a sodium
salt of the oxide. Copper is more resistant but in the presence of air and
especially at temperatures approaching the boiling point of the solutions,
sodium hydroxide is readily contaminated by copper. Other metals are
attacked by fusion with sodium hydroxide in the presence of air, but nickel
and the noble metals are almost unaffected. Some of the non-metals are
also dissolved, as oxy-salts, by aqueous sodium hydroxide but with the
formation of an hydride (or a salt of the hydride) instead of free hydrogen.
On account of its power of emulsifying oils and grease, it is a powerful
cleansing agent for machines, sheet metals, etc. It is used to convert fats
into "hard" soap, and also in the manufacture of sodium and alkaline
bleaching solutions, in the purification of bauxite and as a reagent in the
treatment of organic materials such as paper, artificial silk and dyes..
2.4 Physiological Effects of Sodium Hydroxide
If sodium hydroxide touches the skin and is allowed to remain in contact
for more than a few seconds, it will destroy the skin, causing a serious
chemical burn that will take a long time to heal - and will leave a scar. If it
gets into the eye and is allowed to remain for more than a few seconds, it
will persistently penetrate and destroy the tissues of the eye - resulting in
the loss of the eye or impaired vision due to scaring.
If sodium hydroxide is swallowed, an antidote is required to be taken into
the stomach without delay.
(d) Bypass control with the control valve in the bypass line is the normal
regulation method for rotary pumps.

2.5 Specifications of Commercial Caustic Soda Grades
TABLE 3: CAUSTIC SODA GRADES

3 CHOICE OF PUMP TYPE
3.1 Pump Duty
The pump duty is determined and the preliminary pump type selected in
accordance with GBHE-EDG-MAC-1014.
3.2 Pump Type
(a) For Caustic Soda Strengths up to 50% w/w
For solution strengths up to 50% w/w the preferred type of pump is
the horizontal end-suction back pull-out centrifugal pump to BS
5257.
Alternatively glandless horizontal spindle end suction pumps can be
used of either magnetic drive or canned motor design, to eliminate
seal problems. Normally an inlet strainer would be necessary,
particularly if the liquor to be pumped is not clean. "Slurry" type
designs are available for glandless pumps but they should only be
specified when absolutely necessary.
If vertical spindle submerged pumps are required then these shall
be of the cantilever type, to eliminate problems associated with
intermediate and bottom bearings.
For pit/sump duties horizontal spindle self-priming pumps have
been used successfully.
Vertical in-line pumps have also been used with success, for
general sodium hydroxide pumping duties, but these are non-
preferred due to the multi-trade nature of any maintenance
activities, and the inherent inferior access to seals.
(b) For Caustic Soda Strengths in Range 50% - 100% w/w
Glandless horizontal spindle end suction pumps are recommended.
Vertical spindle cantilever pumps can be used for vessel/pit/sump
duties.

(c) Positive Displacement Pumps
On certain duties such as filtering, it is necessary to use positive
displacement pumps. The helical metallic rotor/double helical
resilient stator design (progressive cavity type) is recommended.
Lobe pumps have also been used successfully.
For pumping weak solutions from effluent pits air-operated double
diaphragm pumps have also been used. These have the advantage
of being portable, but they are, however, inherently inefficient, and
the diaphragm lives are relatively short.
In metering applications, plunger Or diaphragm pump-heads are
used. The plunger models are specified where very accurate
metering is required. Leak tight operation can be obtained by
utilizing various combinations of packing or seals. .The diaphragm
models are of glandless design and are particularly suited for the
more difficult duties, viz strong, hot solutions of caustic soda.
NB: Pressure relief bypass valves are required for any design of
positive displacement pump.
4 RECOMMENDED LINE DIAGRAMS
The following line diagrams are typical only, due to the large possible
permutations of caustic soda solution strengths, duty temperatures, pump
types and seal designs.
Figure 1.1 - Horizontal Glanded, Glandless, and Vertical In-line Pumps
Figure 1.2 - Vertical Spindle Cantilever Pumps
Figure 1.3 - Self Priming Pumps
Figure 1.4 - Reciprocating Plunger Metering Pumps
Figure 1.5 - Positive Displacement Diaphragm Metering Pumps

Figure 1.6 - Water Flushing Arrangement for Double Mechanical
Seal
Figure 1.7 - Water Flush (Quench) Arrangement for Single Hard
Faced (Carbide) Seal and Back-up Lip seal.
5 RECOMMENDED LAYOUT
Pipework should not be run directly above the motor/pump units because
of the risk of leakage and external corrosion.
The availability of water wash facilities should be provided in the near
vicinity.
The specification of the bunded area and its integrity should be checked.
Foundation bolts which penetrate the tiled or special concrete area shall
not be used. Adequate drainage facilities shall be provided to deal with
leakage and contaminated wash water.
Access to drain plugs or valves should be checked.
Additional stop buttons should be located outside the bunded/tiled area
away from the pumps.
Maintenance access around the units should be checked, together with
the adequacy of any lifting/handling facilities.
6 CONSTRUCTION FEATURES
For caustic soda concentrations in the range 0 to 50% w/w, pumps should
be heated and lagged. Electric, LP steam or hot water trace heating may
be used.
For 73% w/w caustic soda liquor, electric or LP steam trace heating
should be designed to maintain the liquor in the pump chamber at
approximately 100o
C at all times.
All pumps should have facilities for emptying the pump chambers and for
washing out.

Pump glands should be fitted with anti-splash guards, and pumps should
be positioned in a suitable catchment tray or area which drains to a sump.
The following types of seals can be used:
(a) Packed glands.
(b) Single mechanical seal/back-up lip seal with low pressure
flush/quench.
(c) Double mechanical seal with pressure water flush.
For materials of construction see Clause 7.
Impellers of centrifugal pumps shall normally be of the shrouded design.
However, where solids are likely to be a problem, open or semi-open
impellers should be specified.
7 MATERIALS OF CONSTRUCTION
For solutions of caustic soda up to 50% w/w strength, pumps should be all
ferrous fitted, e.g. cast iron casing, stainless steel or cast iron impeller,
stainless steel or mild steel shaft. Where gland packings are used, these
should be asbestos/graphite – Crane style SS6 or equivalent.
Where iron and heavy metal contamination of the caustic liquor is
forbidden, titanium pump components have been used. It is important to
look at the service conditions in detail so as to get the materials selection
correct for the particular application.
For solutions strengths in the region of 73% w/w, the casing and impeller
should be 101A Ni-Resist, and other internals of Inconel 600 Shafts,
washers etc. should be Monel 400 and bushes and thrust bearings in
carbon grade CY10F.
For pumping hot anhydrous caustic soda at about 400o
C, the use of
commercially pure nickel material is necessary.

Where mechanical seals are to be used, the component materials should
be carefully selected with the manufacturer in consultation with Materials
Group. A wide range of seal designs and material options are available,
and consideration should be given to all components making up the seal,
viz, flexible member, rotating face, metal parts, stationary seats and
springs etc.
For single mechanical seals, tungsten carbide and silicon free silicon
carbide has been used successfully for the seal faces - this prevents
abrasion of the seal faces by caustic crystal.
Carbon steel is the generally accepted material of construction used for
caustic soda storage equipment. Solutions containing up to 50% caustic
soda are without action on unstressed steel at temperatures up to 40o
C.
The corrosion rate of mild steel in 50% caustic soda liquor is typically
<0.01 to 0.25 mm/yr in the temperature range 50 – 100o
C.
7.1 Nickel and Nickel Alloys
Nickel and nickel alloys are among the most resistant materials for
handling caustic soda and in decreasing order of resistance are nickel,
Inconel, Monel and Incoloy 825. With all but Incoloy 825 contact with
sulfur compounds during fabrication can cause cracking, and specialized
handling and welding techniques are essential during fabrication. The
corrosion rate of nickel and the above alloys in 50% caustic- soda liquor is
negligible at temperatures up to 150o
C.
7.2 Austenitic Stainless Steel
Austenitic stainless steel containing 18% chromium, 8% nickel, 2.5%
molybdenum (AISI types 316, 316L) are resistant to 50% caustic soda
solution at temperatures up to about 100o
C. The corrosion rate should not
exceed 0.001 mm/yr.
7.3 Aluminium, Aluminium Alloys, etc.
Aluminium, aluminium alloys, tin, zinc (galvanizing) - lead and brass are
not suitable for use with caustic soda liquors. Aluminium and its alloys
react rapidly with caustic solutions to produce hydrogen which in certain
circumstances could lead to an explosion hazard.

7.4 Non-Metallic Materials
Non-Metallic Materials - All natural rubbers are resistant to caustic soda
solutions over a temperature range up to 80° C. Gaskets for flanged joints
should be fabricated from acid, alkali, and heat-resisting rubber jointing to
Specification M.228. For higher temperatures butyl rubber should be used.
Thermoplastics are satisfactory up to their maximum design temperature
depending upon the particular use, e.g. – vessel linings, pipe linings,
integral structures with GRP reinforcement etc.
Nylon is only suitable for cold dilute solutions of caustic soda, for instance
10% at room temperature.
Soda lime glass is rapidly attacked; Borosilicate glass (Pyrex) is resistant
to 50% solutions up to 30o
C. Vitreous enamel may be used for cold dilute
solutions but is not suitable for strong solutions.
See Figure 16 - Materials Selection Charts for Caustic Soda Handling.

FIGURE 1.1 LINE DIAGRAM - HORIZONTAL GLANDED, GLANDLESS AND
VERTICAL IN-LINE PUMPS

FIGURE 1.2 LINE DIAGRAM - VERTICAL SPINDLE CANTILEVER PUMPS

FIGURE 1.3 LINE DIAGRAM - SELF PRIMING PUMPS
NOTE
Other possible methods of self priming are:
1 Priming water injection ihto suction line.
2 Suction line priming tank.
3 Manual vacuum priming.
4 Automatic vacuum priming using secondary vacuum system comprising
either a vacuum pump and priming tank or preferably a compressor and
ejector.
5 Foot valve (not recommended).

FIGURE 1.4 LINE DIAGRAM - RECIPROCATING PLUNGER METERING
PUMPS
FIGURE 1.5 LINE DIAGRAM - POSITIVE DISPLACEMENT DIAPHRAGM
METERING PUMPS

FIGURE 1.6 WATER FLUSHING ARRANGEMENTS FOR DOUBLE
MECHANICAL SEAL

FIGURE 1.7 WATER FLUSH (QUENCH) ARRANGEMENT FOR SINGLE
HARD FACED (CARBIDE) SEAL AND BACK-UP LIP SEAL

FIGURE 2 PHASE DIAGRAM of NaOH-H2O

FIGURE 3 VISCOSITIES OF AQUEOUS CAUSTIC SODA SOLUTIONS

FIGURE 4 VAPOR PRESSURE OF AQUEOUS CAUSTIC SODA SOLUTIONS

FIGURE 5 ENTHALPY CONCENTRATIONS FOR AQUEOUS CAUSTIC
SODA SOLUTIONS

FIGURE 6 SPECIFIC GRAVITY FOR AQUEOUS CAUSTIC SODA
SOLUTIONS

FIGURE 7 DILUTION OF CAUSTIC SODA LIQUOR

FIGURE 8: THERMAL CONDUCTIVITY OF AQUEOUS CAUSTIC
SODA SOLUTIONS

FIGURE 10 BOILING POINTS OF STRONG CAUSTIC SODA SOLUTIONS
AT REDUCED PRESSURE

FIGURE 11 COMMENCEMENT OF FREEZING OF CAUSTIC SODA
SOLUTIONS (0 - 52% W/W)

FIGURE 12: TEMPERATURES ATTAINED ON DISSOLUTION
OF ANHYDROUS CAUSTIC SODA

FIGURE 15 DENSITY - CONCENTRATION TABLES· FOR CAUSTIC SODA
SOLUTIONS AT 60o
F (15.5o
C)

FIGURE 16 MATERIAL SELECTION CHART FOR CAUSTIC SODA
HANDLING

DOCUMENTS REFERRED TO IN THIS ENGINEERING DESIGN GUIDE
This Engineering Design Guide makes reference to the following documents
BRITISH STANDARDS
BS 5257 Horizontal End-Suction Centrifugal Pumps
(referred to in 3.2)
GBHE ENGINEERING DESIGN GUIDES
GBHE-EDG-MAC-1014 Integration of Special Purpose Centrifugal
Pumps into a Process (referred to in 3.1)
JOINTING Acid, Alkali and Heat-Resisting
Rubber jointing (referred to in 7.4).

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