cryogenic piping design

7/28/2019 Cryogenic Piping Design

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Optimum Design of Cryogenic Pipe Supports

Hyun-Joo, Chang

General Manager

Seung-Nam, Shin

Piping Stress Engineer

Hyundai Engineering Co., Ltd

Abstract

Cold insulation pipe supports have been widely used in a number of chemical

plants including LNG receiving terminal. This paper presents a theoretical and

practical study of optimum design of cryogenic pipe supports required to

design LNG receiving terminal. A solution for optimum design of cryogenic pipe

supports is obtained and practical results are presented.

It is shown that when we design cryogenic pipe supports, we have to consider

structural characteristics, design load, requirement from the owner and

economic aspect for each type of supports such as shoe, guide, stop and

trunnion. So, it is very important to clarify the behavior of cryogenic piping

system including pipe support during normal operation of LNG receiving

terminal. For this purpose, not only theoretical but also practical approaches

have been used to clarify the behavior of cryogenic piping system during

normal operation and initial start-up.

This design of cryogenic pipe supports has been validated by comparison with

other type of cryogenic pipe supports, and confirmed by applying to Inchon

LNG receiving terminal. It is noted that this design is efficient and applicable to

future LNG receiving terminal project.

The following issues are presented in this paper.

z Behavior of cryogenic piping system during initial start-up

z Behavior of cryogenic piping system during normal operation

z Characteristics of cryogenic piping system and pipe supports

z Requirements for cryogenic pipe supports


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z Optimization of cryogenic pipe supports

z Comparison with other type of cryogenic pipe supports

z Confirmation of cryogenic pipe supports

1. Introduction

LNG (Liquefied Natural Gas) has been widely used as a clean energy

nowadays, and there are so many large LNG receiving terminals under

construction accordingly. Among these large LNG receiving terminals, Inchon

LNG terminal in Korea is one of the largest LNG receiving terminals. We,

Hyundai Engineering Company, participated in design of Inchon LNG terminal

over 10 years. We have much experience in designing cryogenic piping, and

we would like to share this experience on this subject.

As a matter of fact, since the boiling point of LNG is such a low temperature,

what is so called cryogenic, as under -162 that extremely superior insulationproperty, durability and also stable function are required for supporting devices

such as shoe, stop, and anchor to be used at LNG receiving terminal. The

problems encountered in cryogenic piping system are as follows;

embrittlement of materials, icing around/between the cryogenic pipe support,

pipe insulation and steelwork, large displacements (due to the thermal

expansion and contraction), rapid change of phase due to large heat fluxes

(big delta T), and small latent heats of the fluids involved. Thus, extremely high

reliability is required to design cryogenic pipe support system.

From the general point of view, supports must be designed to meet all static as

well as dynamic operational conditions to which the piping may be subjected.

The support system must provide for and control, subject to the requirements

of the piping configuration, the movement due to the thermal expansion and

contraction of the piping and the connected equipment. Furthermore, the

correct and economical selection of the pipe supports for cryogenic piping

system usually presents difficulties of varying degree, some relatively minor

and others of a more critical nature. Proper selection of cryogenic pipe support

should be the objective of this paper. A good pipe support design begins with


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good piping design and layout. That means many pipe support problems may

be minimized or avoided if proper attention is given to the means of support

during the piping layout design phase. Therefore, behavior and requirements

of cryogenic piping system during normal operation and initial start-up are

presented here. This paper also provides guidelines for the design and layout

of cryogenic piping and pipe supports found in LNG receiving terminal and

related processing plant.

2. Features of Cryogenic Piping System

Heat is continuously entering the piping through the insulation and supports.

This heat will make the liquid contents boil. For this reason heat leak must be

minimized. From an economic point of view, the thermal efficiency of the piping

system must be carefully considered since the heat addition to the system will

ordinarily result in loss of product. So there must be the need for

understanding cryogenic piping system.

In order to obtain a better appreciation of the special consideration involved in

cryogenic pipe support system application, it was felt that it would be

necessary to review the behavior of materials at cryogenic temperature and

the physical and thermodynamic property of cryogenic piping and pipe support

system. These considerations are presented in this section.

2.1 Materials used in Cryogenic Piping Systems

Important consideration in the selection of materials for cryogenic piping

systems include suitable mechanical and physical properties, compatibility with

process fluids, fabricability, cost, and compliance with regulatory codes such

as ASME B31.3. It is recognized that certain materials tend to become brittle at

low temperature and maybe subject to failure which would not usually occur at

normal temperature or at elevated temperature. The transition temperature at

which certain materials become brittle is not well defined. Some ferrous

materials may pass through the transition range at normal temperature, while

others may not become brittle until it reaches low temperatures. Because of


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embrittlement of materials, carbon steel can not be used for cryogenic piping

systems. Therefore, we have to use ferrous alloys.

Table 1 - Typical Ferrous Alloys used in Cryogenic piping

AlloyMinimum

Temperature

ASME

DesignationRemark

C-Mn steel -46 A 333 Gr.1

2 1/4% Ni steel -73 A 333 Gr.7

3 1/2% Ni steel -101 A 333 Gr.3

9% Ni steel -196 A 333 Gr.8

304 Stainless

steel -254

A312

304L Stainless

steel-254 A312

316 Stainless

steel-196 A312

316L Stainless

steel-196 A312

347 Stainless

steel-254 A312

Ferrous alloys most often encountered in cryogenic piping applications are

usually classified as ferritic or austenitic types. (Please refer to Table 1.) The

terms austenitic and ferritic refer to the predominant crystallographic phases

ferrite or austenitic, which are body centered cubic (BCC) and face centered

cubic (FCC), respectively. Most of the austenitic alloy steels used in cryogenic

piping are chromium-nickel stainless steels of the AISI 300 type, such as 304,304L, 316, and 316L. Other stainless steels classified as martensitic, duplex,

and precipitation hardening also exists; however, the preceding alloys are most

commonly used in cryogenic piping for LNG receiving terminal and distribution

applications. Of the 300 Series alloys, the AISI 304 composition is the most

popular as measure by tonnage.


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As can be seen in Table 2, thermal expansion for austenitic alloy steels used in

cryogenic piping is much larger than that of carbon steel. This large thermal

expansion makes large displacements (expansion and contraction) of material.

This makes it more difficult to design cryogenic piping system than to design

hot insulated piping system.


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Table 2 - Typical mechanical and Physical properties of Ferritic Alloys used in Cryog

Alloy

ASME

spec.

Temp.

( )

Ultimate Tensile

Strength (MPa)

0.2% Offset

yield strength

(MPa)

% Elong. in

5.1cm (%)

Charpy Impact

Strength (Joules)

The

(m

C-Mn steel A 333

Grade 1

RT

-46379 207 21

95

68

2 /4% Ni steel A 333

Grade 7

RT

-73

448

517

241

27618

79

27

31/2% Ni steel A 333

Grade 3

RT

-101

689

11379

517

58618

130

30

9% Ni steel A 333

Grade 8

RT

-196

793

1172

621

931

25

27

64

34

304Stainless steel

A 312TP304

RT-254

5861724

262483

453

156102

304L

Stainless steel

A 312

TP304L

RT

-254

552

1551

255

469

45

31

81

81

316

Stainless steel

A 312

TP316

RT

-198

600

1358

262

448

45

56

-

-

316L

Stainless steel

A 312

TP316L

RT

-196586 262 45 -

347

Stainless steel

A 312

TP347

RT

-254

621

1586

469

483

50

38

81

61


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2.2 Insulation for Piping System

Most piping in liquid cryogenic service is insulated. The reasons a line would

not be insulated are that (1) its use is very infrequent and brief; (2) it is a

temporary installation;or (3) the refrigeration losses are inconsequential.

The type of insulation used for cryogenic piping includes (1) expanded foams

such as polyurethane and foamglass, (2) powder insulations such as perlite,

and (3) vacuum-insulated pipe. For an insulation system to remain effective,

the vapor barrier system must keep atmospheric moisture from entering the

insulation space and freezing against the cryogenic line. When this occurs, the

ice that is formed will degrade or destroy the insulation system.

When the cryogenic liquid is colder than the boiling point of oxygen (-297 or

-183 ), oxygen can condensate out of the air and collect in the insulation

space. For this situation, the insulation system should be noncombustible in

the presence of oxygen. Heat leak by conduction and radiation is reduced by

the laminar radiation shielding. The heat leak by convection is reduced by the

vacuum.

When cold insulation is required, the entire system shall be fully insulated,

including all piping components, piping/tubing of insulated instruments, drains,

equipment nozzles and supports. And all metal parts which protrude through

the insulation shall be insulated.

The typical values for thermal conductivity are shown in Table 3. The expanded

foam insulation uses a covering to provide the vapour barrier protection. The

initial capital cost is usually lower than the other system, but more frequent

maintenance is required to maintain a tight vapour barrier.

Table 3 - Thermal Conductivity of Pipe Insulation Materials at Insulation Mean

Temperature of -100


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InsulationThermal conductivity

[Btu/(hft 2)]

Thermal conductivity

W/(mK)

Urethane Foam 0.012 .021

Foamglass 0.024 .042

Perlite (at atmospheric

pressure)0.018 .031

Perlite (vacuum at 1m) 7.9 x 10 4 1.37 x 10 3

Laminar radiation

shielding

(vacuum at 1m)

2.1 x 10 5 3.63 x 10 5

2.3 Flexibility Analysis for Cryogenic Piping System

Piping flexibility analysis is an important design consideration because the

large difference between ambient and cryogenic temperatures will result in

significant thermal contraction. Moreover this piping flexibility analysis should

be carried out before cryogenic pipe support design. When the amount of pipe

movement exceeds the capacity of a pipe support system, a fixed support and

more expansion loops should be designed in order to reduce the amount of

pipe movement.

The flexibility analysis of the cryogenic piping must consider the full

temperature range as well as any other conditions with severe temperature

difference which may occur during upset, thaw, or cool-down. And cryogenic

pipe support must be designed accordingly.

The analysis methods used are similar to those required for conventional

piping system. The one difference is that piping in cryogenic services contracts

rather than expands as it is the case with high temperature services. However,

since the analyst can calculate the resulting contraction, the analysis method

becomes identical to those used for conventional piping systems.

For safe design, flexibility analysis for cryogenic piping system is usually


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carried out to meet the engineering requirements of ASME B31.3, Process

Piping Code.

2.4 Requirements for Cryogenic Pipe Supports

When an un-insulated cryogenic piping is supported, a portion of the pipe

support will be at cryogenic temperature. Low temperature should be

considered when selecting the materials for the pipe support and its hardware.

For low temperature service, in addition to heat loss and gain, the problem of

atmospheric condensation must be considered, and such lines are usually

insulated with a material that has an outer covering or seal called a vapour

barrier. This barrier prevents the insulation from absorbing moisture. For this

reason it is not permissible to penetrate the insulation with load-carrying

members such as the legs of a conventional high-temperature shoe/saddle or

a pipe clamp. Since most low-temperature insulation has low compressive

strength, it is necessary to provide shields to the line the piping insulation and

to spread out the bearing area sufficiently to prevent crushing of the insulation.

Such shields should fit the outer diameter of the insulation and cover 180

degree of arc.

For cryogenic piping system, pipe support must be outside the insulation,

withstand loads from the insulation material, must be ductile at cryogenic

temperature, and has a relatively low thermal conductivity. And the vapour

barrier must be left undisturbed. Therefore, cryogenic pipe supports shall meet

the following requirements as a minimum.

a. Supports shall be lighter in weight when compared with wooden block.

b. High reliability in water and resistance to oil and corrosion Supports shall

not need and preservative treatment such as creosote impregnation.

c. High weather tightness Supports resist weathering and corrosion in long

term outdoor use.

d. Supports shall exceed in physical strength against compression, bending

and shearing.

e. Supports shall be suitable for mass production.


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f. Forming incorporated with other material shall be possible.

g. Free of grains, homogeneous and standard quality cradles shall be

obtained in large quantity at the same time.

h. Low water absorption Supports shall not incur cracks from icing during

storage or operation.

i. Heat and Flame resistance Flammability of material shall be

self-extinguished in accordance with ASTM D1692.

2.5 Consideration of Cryogenic Pipe Supports

High density cradle type of cryogenic pipe supports shall incorporate a molded

heavy density layer bonded with a stainless steel weather shield and

assembled with a steel cradle. The high density layers shall be stepped and,

together with the metal jacketing, sufficiently extended to facilitate

incorporation within the adjacent insulation system. All Joints between

supports and insulation shall be tightly fitted together and staggered with as

few voids as possible in order to avoid icing due to heat leakage.

Cryogenic pipe supports shall meet the design requirements in respect of

compressive strength under sustained load, thermal conductivity, coefficient of

friction, service temperature and flammability.

3. Optimization of Cryogenic Pipe Support

As reviewed in the previous section, an extremely high degree of reliability is

required in recent days in the field of pipe supporting system design such as

LNG receiving terminal.

Conventionally, wooden heat insulators have been used for piping system

supports in these plants. However, these materials involve difficulties of

availability and unstable quality. Furthermore, this material is very heavy and

expensive. And often delivery is very long. Therefore, this kind of wooden

block can not meet the requirements mentioned above. So we have to find and

develop a better one. Urethane block made of high density polyurethane foam

which has low thermal conductivity is a better cryogenic pipe support among


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various kinds of materials. They have been already used, and well received in

various plants. And we are going to present optimized cryogenic pipe supports

made of high density polyurethane foam.

3.1 Polyurethane Cradle Supports

Shoe type of support mainly consists of polyurethane cradle and a steel

load-bearing plate. It is used for sliding supports, guide supports, hanger

supports, stanchion, trunnion and etc to avoid the condensate and formation of

ice, around each support, which would restrict free movement of the piping.

Additionally, under certain thermal conditions, direct contact between the pipe

and the structure could produce local brittleness of the structure itself.

Figure 1 shows typical cryogenic pipe support detail drawing, where B is cold

insulation thickness.

Fig. 1 Cryogenic Pipe Support Detail Drawing

Cradles shall be high density polyurethane foam which shall possess a unique


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cellular structure. And each cold insulated pipe supports shall have a vapour

barrier. Easy assembling and finishing polyurethane cradle to the pipe line is

also required. Design strength shall be based on ultimate compressive

strength with a minimum safety factor of 5, or that which results in a 1%

deflection, whichever is less, and shall have the following properties;

a. Polyurethane foam shall satisfy the flame spread requirements of UL94.

The minimum percentage of weight retention of the foam when tested in

accordance with ASTM D3014 shall be 75%.

b. Average density of PUF cradle shall be verified by dividing the weight of

the cradle by its volume. Average density shall be within 5% of the

specified density, for both 224kg/m3 and for 320kg/m3 PUF cradles.

Average density for 160kg/m3 shall be within -0% and +10%.

c. Minimum value for the ultimate compressive strength for samples taken

from the core i.e., within the middle 60% of the thickness for all densities

shall be within 10% of the specified values.

d. The thermal conductivity of the polyurethane foam at -160 , in accordance

with ASTM C177, shall be within +/-5% of the values specified in Table 4.

Samples shall be taken from the core within the middle 60% of thickness,

where it is practical.

Table 4. Mechanical Characteristics of High density Polyurethane

Pipe SizeCore

Density

Stress at 1%

deflection

Minimum

Compressive

Strength

Thermal

Conductivity

(W/mk)

1/2 to 8 160 kg/m3 3.2 kg/cm2 18.5 kg/cm2 0.022

10 to 72 320 kg/m3 12.8 kg/cm2 70.4 kg/cm2 0.032

- Finish

Cradle ; Protective coating

Bearing Plate and Shoe ; Painted after pickling or hot dip galvanized

Masking ; The bore of the cradle is completely covered with masking tape


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Bonding ; The bearing plate is bonded to the cradle at the shop and the

cradle is bonded to the pipe by field fabricator.

- Service Temperature Limit ; -196 to 80

- Size Range ; 1/2 through 72 pipe size

Pipe support type varies in accordance with insulation thickness. Figure 2

shows type selection for pipe according to insulation thickness which has been

adopted for Inchon LNG receiving terminal in Korea.

Fig. 2 Type Selection for Pipe and Insulation Thickness


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3.2 Bearing Plate

The material for the bearing plate which prevents crushing of the insulation

shall be carbon steel (ASTM A36 or equivalent) fully killed open-hearth, electric

furnace, or basic-oxygen steels. Steel band strapping seals are to be pusher

type seal.

3.3 Adhesive, Protect ive Coating and Seal

The adhesive shall be applied to a thickness of 0.015inch (0.38mm) when

Fosters 81-84 is used. Sufficient adhesive shall be used to fill any gaps or

voids in the surfaces to be bonded. The bond adhesive shall be allowed to cure

overnight at room temperature. If the adhesive material recommended by the

PUF manufacturer is other than the specified one, the substituted adhesive

material and applied thickness must be properly tested prior to being used. All

surfaces of the polyurethane which requires adhesive bonding, protective

coating of seal shall provide an appropriate anchor profile. Any waxy, smooth

surfaces such as mold release film must be removed prior to the application of

adhesive or protective coating.

a. Adhesive

The polyurethane cradles shall be bonded to the bearing plate/bearing plate

assemblies by the polyurethane foam (PUF) manufacturer. Multilayer cradles

are also bonded together by the polyurethane foam (PUF) manufacturer. The

adhesive for the above bonding is normally Fosters 81-84, manufactured by

the Foster Products Division of the H.B. Fuller Co.

b. Protective Coating

Monolar mastic 60-91 (gray) adhesive/coating available from the Foster

products Division of H.B. Fuller Co. and H.B. Fuller licensees to be applied to a

dry thickness of 0.034 inch (0.86mm). The manufacturer shall supply

approximately 10% of the quantity of protective coating used in the shop

fabrication of cold insulated pipe shoe for field repair of minor breaks in the

protective seal.


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c. Seal

The interface joints between the cradle and bearing plate shall be completely

sealed with Butyl rubber sealant, to prevent water ingress. Sealant is normally

Childers CP-76, Childers Products Company, Fosters 95044 (Fuller Company,

Foster Products Division) or equivalent.

The interface surfaces between upper and lower cradles shall be completely

sealed with Childers CP-76, Foster 95-44 or an equal sealant.

d. Masking Tape

The inside radius surfaces of the cradle shall be completely covered with

masking tape.

3.4 Beam Width and Allowable Moving

The anticipated movement at each support point dictates the basic type of

support required. Each type of support selected must be capable of

accommodating movements obtained by piping flexibility analysis. Both

longitudinal and horizontal movement must be evaluated.

Because of large displacements (expansion and contraction) of material used

for cryogenic piping system, displacement control becomes very important.

These displacements due to thermal contraction can be predicted by piping

flexibility analysis. For this reason supporting one line from another is

forbidden for cryogenic piping. The Figure 3 shows recommended beam width

and its allowable moving, which has been adopted for Inchon LNG receiving

terminal in Korea. Therefore, detail design should be applied in consideration

of pipe temperature under contraction and distance from anchor point. And

special length support is available upon request for need or more allowable

moving.


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Fig. 3 Beam Width and Allowable Movement

In addition to displacement control, the cryogenic pipe supports has to slide

smoothly in order to avoid icing around/between the cryogenic pipe support

and pipe insulation. Thus PTFE sliding plate shall be used to minimize

horizontal forces caused by frictional resistance for cryogenic piping system.

3.5 Field installation Check Point

Based on the experience, we have the field installation check point as follows;

a. As soon as the package is opened, check the support assembly if there is

any damage. And if the damage is small such as coming off of coating, the

damage should be repaired at the field.

b. Clean the surface of pipe to remove all the foreign objectives adhered

such as rust, vapour, oil, dust and etc.

c. As the supports are installed at the center of existing beam or at off-set

position depending on the requirement, the installation position shall be

determined and clearly marked.


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d. Remove the masking tape which is adhered on the cradle bore.

e. Apply the adhesive uniformly on the cradle bore, then, press the support

assembly against the pipe and fasten firmly together by using the steel

band until the adhesive harden.

f. The time to release the steel band is depended on the open air

temperature. When the temperature is over 18 , the steel band may be

released after 12 hour duration.

g. Touch up the portion with protective coating agent where the protective

coating is come off.

3.6 Thermal Bowing owing to Two Phase Flow

Consideration of the cryogenic fluid properties has an effect on the piping

arrangement. Because the cryogenic fluid is colder than ambient air, the

continuous heat leak from ambient air to the piping system is a design

consideration. Because of rapid change of phase due to large heat fluxes

caused by this kind of heat leakage, there is the temperature difference

between top and bottom of the pipe cross section and two phase flow. The

effect of two phase flow is much more complicated than that of single phase

flow. This is attributed to the fluctuations of flow rate, density and pressure

gradients, as well as oscillations due to compressibility of the partial gas fluid.

This continuous heat leakage also causes thermal bowing, which should be

avoided.

When a cryogenic liquid line is initially put in service, the warm piping will

cause liquid flash-off, which could restrict the flow during the two-phase flow

transient period. When it is possible to pre-cool the lines, the piping can be

sized for liquid phase flow, which will result in small piping. If rapid cool-down is

required, the piping must be sized for two-phase flow. This rapid cool-down

also causes thermal bowing. Undesirable heat transfer and heat loss is

therefore reduced.

Considering unexpected thermal bowing and fluctuations of flow rate, pipe

support span for cryogenic piping shall be much shorter than that of

hot-insulated piping. When practical, a support should be located immediately


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adjacent to any change in direction of the piping.

4. Conclus ions

This paper has shown in such a way as to ensure proper support under all

operating and environmental conditions and to provide for expansion /

contraction, PTFE sliding plate, thermal bowing, and insulation protection for

cryogenic piping system.

In conclusion, it appears that the following points represent a reasonable point

of cryogenic pipe support design from the theoretical and practical study and

by applying to Inchon LNG receiving terminal

1. Cryogenic pipe supports shall be designed to minimize thermal

conduction which could adversely affect the fluid in the pipe and/or the

surrounding structure.

2. Cryogenic supports shall be designed taking into account warm-up and

cool-down conditions. So piping flexibility analysis is necessary before

cryogenic pipe support design. Adequate systems shall be used in order

not to induce additional stresses on insulation material.

3. At support location, insulation material shall be high density foam

(160kg/m3 or higher), and a maximum deflection of 1% on insulation

cradle shall be respected.

4. Because of large displacements (expansion and contraction) of material

used for cryogenic piping system, supports selected must be capable of

accommodating movements.

5. PTFE sliding plate shall be used to minimize horizontal forces caused by

frictional resistance for cryogenic piping system.

6. Considering unexpected thermal bowing and fluctuations of flow rate,

pipe support span for cryogenic piping shall be much shorter than that of

hot-insulated piping.

All of the foregoing topics are very important and must be studied to design

cryogenic piping system from the support point of view and to provide a

general understanding and the basis for cryogenic pipe support design guide.


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Further work on this topic includes cryogenic pipe support subject to surge

force and steady state vibration like pulsation.

REFERENCE

1. Paul R. Smith and Thomas J. Van Laan ; Piping and Pipe Support

Systems, Design and Engineering, McGraw-Hill Book Company

2. Piping Design and Engineering, ITT Grinnell Industrial Piping, Inc.

3. Ernest Holmes ; Handbook of Industrial Pipework Engineering,

McGraw-Hill Book Company

4. MSS SP-58, Materials and Design of Pipe Supports

5. MSS SP-69, Selection and Application of Pipe Supports

6. MSS SP-89, Fabrication and Installation of pipe Supports

7. BS 3974, Specification for Pipe Supports, Part 1, 2 and 3

8. ASME B31.3, Process Piping

9. M. W. Kellogg, Pipe Support Components and Fabricated Assemblies

10. N.H.K Spring Co., Ltd, Inspection Report for Cryogenic Pipe Support,

M.W. Kellogg Type

11. Mohinder L. Nayyar ; Piping Handbook, McGraw-Hill Book Company

cryogenic piping design

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