NACE Standard RP0178-95Item No. 21022

StandardRecommended Practice

Fabrication Details, Surface Finish Requirements,and Proper Design Considerations for Tanks

and Vessels to Be Lined for Immersion Service

NACE International issues this standard in conformance with the best current technologyregarding the specific subject. This standard represents a consensus of those individual memberswho have reviewed this document, its scope, and provisions. It is intended to aid themanufacturer, the consumer, and the general public. Its acceptance does not in any respectpreclude anyone, whether he has adopted the standard or not, from manufacturing, marketing,purchasing, or using products, processes, or procedures not in conformance with this standard.Nothing contained in this NACE International standard is to be construed as granting any right, byimplication or otherwise, to manufacture, sell, or use in connection with any method, apparatus,or product covered by Letters Patent, or as indemnifying or protecting anyone against liability forinfringement of Letters Patent. This standard represents minimum requirements and should in noway be interpreted as a restriction on the use of better procedures or materials. This standard isnot intended to apply in all cases relating to the subject. Unpredictable circumstances may negatethe usefulness of this standard in specific instances. NACE International assumes noresponsibility for the interpretation or use of this standard by other parties and acceptsresponsibility for only those official NACE International interpretations issued by NACEInternational in accordance with its governing procedures and policies which preclude theissuance of interpretations by individual volunteers.

Users of this standard are responsible for reviewing appropriate health, safety, and regulatorydocuments and for determining their applicability in relation to this standard prior to use. ThisNACE International standard may not necessarily address all safety problems and hazardsassociated with the use of materials, operations, and/or equipment detailed or referred to withinthis document.

CAUTIONARY NOTICE: NACE International standards are subject to periodic review and may berevised or withdrawn at any time without prior notice. The user is cautioned to obtain the latestedition. NACE International requires that action be taken to reaffirm, revise, or withdraw thisstandard no later than five years from the date of initial publication. Purchasers of NACEInternational standards may receive current information on all standards and other NACEInternational publications by contacting the NACE International Membership ServicesDepartment, P.O. Box 218340, Houston, Texas 77218-8340 (telephone +1 281/228-6200).

Reprinted May 1994Reaffirmed March 1991

Revised 1989Approved 1978

NACE InternationalP.O. Box 218340

Houston, Texas 77218-8340+1 281/228-6200

©1991, NACE International

RP0178-95

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Foreword

When specifying tanks for immersion service that are to be internally lined to control corrosion and/or preventproduct contamination, special design, fabrication details, and surface finishing requirements must be taken intoconsideration to obtain the desired performance of these linings.

To prevent product contamination and to extend the service life of the vessel, linings are often applied to bringthe corrosivity of the product on the vessel to a point that is low enough to be of no significance. As the corrosivity ofthe product increases, the design of the vessel becomes more critical, relative to the performance of the lining.Where a tank is to be lined for contamination prevention purposes only, certain compromises may be economicallyjustifiable without sacrificing the lining performance.

This revision of NACE Standard RP0178-78 was prepared by NACE International Task Group T-6G-27, acomponent of Unit Committee T-6G on Surface Preparation for Protective Coatings, and is issued under theauspices of Group Committee T-6 on Protective Coatings and Linings. The original RP0178-78 was prepared in1978 by Task Group T-6A-29 of Unit Committee T-6A on Coating and Lining Materials for Immersion Service incollaboration with Unit Committee T-6H on Application and Use of Coatings for Atmospheric Service (currently titledCoating Materials for Atmospheric Service) and was issued under the auspices of Group Committee T-6 onProtective Coatings and Linings.

NACE Publication TPC 2, “Coatings and Linings for Immersion Service,” should be used as a guide for allareas of responsibility regarding coatings.

This standard is issued to present recommended practices for the design, fabrication, and surface finish ofmetal tanks and vessels that are to be lined for corrosion resistance and to prevent product contamination. Theserecommended practices are considered necessary by lining suppliers, applicators, and users of such tanks throughtheir experiences with them.

Explanation is given as to how the suggested practices govern the quality of lining applications. Appendix Ashows both good and bad design practices on tanks, while Appendix B contains a list of suggested responsibilitiesfor the coating applicator to ensure the best protective coating available. Appendix C is a visual and writtendescription of the degree of surface preparation of welds in tanks and vessels prior to lining. (Please note: The visualcomparator referenced in Appendix C illustrates various degrees of surface finishing for welds prior to coating orlining. Welds included on the visual comparator include full seam welds, skip welds, butt welds, lap welds, etc. Thevisual comparator is available from NACE International Headquarters. For more information contact the NACEInternational Membership Services Department, P.O. Box 218340, Houston, TX 77218-8340.) Also note that thewritten description of the various degrees of surface preparation of welds in the appendix of this standard takesprecedence over the graphics which are only pictorial representations of welds and grinding finishes and are in noway intended to be representative of the integrity of the welds and over the companion visual comparator. NOR ISTHE “AS IS” ORIGINAL WELD A TYPICAL WELD; RATHER, IT IS ONLY INTENDED TO ILLUSTRATEDEFECTS IN WELDS WHICH MUST BE CORRECTED PRIOR TO COATING AND LINING. Further, goodwelding practices and welding codes such as AWS, AWWA D-100. API 650 and 1104, ASME, ANSI, and AARtake precedence over a written description of the various degrees of surface preparation of welds in this appendix,the accompanying visual comparator, and the graphics.

NACE International gratefully acknowledges the contributions of the following companies in the preparation ofthe welding samples and the fabrication of the die from which the plastic replicas have been molded:

Ausimont, Morristown, NJHouston Lighting & Power, Houston, TXS.G. Pinney & Associates Inc., Port St. Lucie, FLThe Sherwin-Williams Company, Cleveland, OH

NACE International also gratefully acknowledges the assistance of KTA-Tator Inc., Pittsburgh, PA, in developing theweld pattern that was used to mold the plastic replica of weld samples.

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This standard represents a consensus of those individual members who have reviewed this document, its scope,and provisions. Its acceptance does not in any respect preclude anyone, whether he has adopted the standard ornot, from manufacturing, marketing, purchasing, or using products, processes, or procedures not in conformancewith this standard. Nothing contained in this NACE International standard is to be construed as granting any right,by implication or otherwise, to manufacture, sell, or use in connection with any method, apparatus, or productcovered by Letters Patent, or as indemnifying or protecting anyone against liability for infringement of Letters Patent.This standard represents minimum requirements and should in no way be interpreted as a restriction on the use ofbetter procedures or materials.

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NACE InternationalStandard

Recommended Practice

Fabrication Details, Surface Finish Requirements, andProper Design Considerations for Tanks and Vessels

to Be Lined for Immersion Service

Contents

1. General..................................................................................................................... 12. Design Requirements................................................................................................ 13. Fabrication Requirements ......................................................................................... 24. Surface Finish Requirements.................................................................................... 2Appendix A—Fabrication Details, Surface Finish Requirements, and

Proper Design Considerations for Metal Tanks and Vessels to BeLined for Immersion Service ..................................................................................... 3

Appendix B—Suggested Responsibilities ....................................................................... 8Appendix C—Generic and Graphic Descriptions of Various Degrees

of Surface Finishing of Welds That May Be Specified in Preparationfor Lining of Tanks and Vessels ................................................................................ 9

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Section 1: General

1.1 Scope

This recommended practice provides requirements for thedesign, fabrication, and surface finish of tanks necessaryto achieve the specified lining integrity required for theservice to which the lining will be subjected, whether it befor corrosion control or to prevent contamination of theproduct being stored. Suggestions are given in AppendixB for the responsibilities of the purchaser (user), fabri-cator, and lining applicator regarding design specifi-cations and inspections.

1.2 The recommended practices in this standard canalso be used in the design, fabrication, and surface finishof tanks or vessels for services other than immersion,such as dry bulk storage of solid materials.

1.3 Definitions

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1.3.1 Linings: Surface barriers, usually thin filmsless than 20 mils (0.5 mm) thick applied as either alining or a coating. In common usage, the terms“coatings” and “linings” are used interchangeably, butin this document, only the term “linings” will be used.The requirements contained herein may or may notapply to heavier, thick film coatings, sheet linings,trowel applied and gunite finishes, plasma, flame-sprayed coatings, fiber-reinforced plastic linings, etc.

1.3.2 Surface Finish: The degree of smoothness of asurface produced by the removal of sharp edges andthe appropriate surface preparation of welds andother rough areas. The term “surface finish” is alsoused to characterize the degree of smoothness thatis necessary to attain a surface to which the liningcan be applied satisfactorily per the lining speci-fication.

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Section 2: Design Requirements

2.1 Accessibility

2.1.1 All surfaces of the tank interior shall be readilyaccessible for surface preparation and lining appli-cation (Figures 1 through 10, Appendix A).

2.1.2 The minimum manway diameter for workingentrance and safety reasons during the lining appli-cation shall be as large as practical for the vesselbeing lined.

2.1.2.1 If possible, at least one manway shall belocated near ground (work) level, except in tanksdesigned to be buried below grade.

2.1.3 Additional manways and opening(s) should beprovided as needed to facilitate ventilation and safetyrequirements.

2.2 Joints

2.2.1 Butt weld joints shall be used wheneverpossible (Figure 5, Appendix A).

2.2.2 Rivets shall not be used.

2.2.3 Avoid the use of internal bolted connections.

2.2.4 Continuous lap welded joints are permissiblebut not preferred. For sheet lining material, this typeof construction may not be acceptable.

2.3 Connections

2.3.1 All connections to the tank shall be flanged.

2.3.2 Threaded connections shall not be used invessels operating in corrosive environments (Figure4, Appendix A). However, if threaded connectionscannot be avoided in corrosive environments, theseparts shall be fabricated of corrosion resistant mate-rials or constructed as shown in Figure 10. (Caution-ary note: See caption for Figure 8 of Appendix A forthe effect of exposed, uncoated dissimilar metalareas.)

2.3.3 Nozzle connections to be lined shall be asshort as possible and be a minimum of 2 in. (5 cm)diameter (Figure 4, Appendix A). Connections lessthan 2 in. (5 cm) diameter shall be suitably attachedthrough a reducing flange (Figure 10, Appendix A).Where thick film linings, trowel-applied, are required,allow additional nozzle inside diameter for liningthickness.

2.4 Appurtenances Inside the Tank

2.4.1 The requirements of Sections 2 and 3 of thisstandard shall apply to any item to be installed insidea tank that is to be lined. Such appurtenancesinclude agitators, anti-swirl baffles, outlet connec-tions, gauging devices, and internal piping.

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2.4.2 If appurtenances inside the tank, including nutsand bolts, cannot be lined, they shall be made ofcorrosion-resistant materials. (Cautionary note: Seecaption for Figure 8 of Appendix A for the effect ofexposed uncoated metal areas.)

2.4.3 If bolted connections are necessary and cannotbe made of corrosion-resistant materials, the matingsurfaces shall be lined before assembly. Matingsurfaces and the sealing surfaces of nuts and boltsshall be gasketed to protect the lining.

2.4.4 Dissimilar metals shall be electrically isolatedfrom the steel tank surface wherever possible. Butwhere dissimilar metals are used selection shall besuch that the galvanic effect is minimized. Othercorrosion mitigation methods may be required(Figure 8, Appendix A).

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2.4.5 Heating elements shall be attached with aminimum clearance of 6 in. (15 cm) from the tanksurface.

2.5 Structural Reinforcement Members

2.5.1 Structural support members should beinstalled on the exterior of the tank. However, if suchmembers are installed internally, they shall befabricated of simple shapes such as smooth roundbars or pipe for ease of applying the lining material.

2.5.2 The use of internal flanged connections, stif-fening rings, reinforcement pads, angles, channels, I-beams, and other complex shapes should beavoided. If they must be installed internally, thesemembers shall be fully welded and welds and sharpedges ground and radiused a minimum of 1/8 in. (3mm); 1/4 in. (6 mm) radius is preferred (Figures 1and 6, Appendix A).

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Section 3: Fabrication Requirements

3.1 All requirements given in Section 2 on DesignRequirements shall apply to all fabrication procedures.

3.2 All welding shall be of the continuous type. Inter-mittent or spot welding shall not be allowed.

3.3 Fillets and corners must be accessible for grinding.

3.4 Field tanks fabricated for use with high heat curedlinings (e.g., unmodified phenol formaldehyde thermo-setting coatings) should have bottoms suitably insulatedand installed on properly drained foundations to facilitateproper cure of the lining on the floor of the tank. Since thesand-filled earthen foundation, concrete pad, or othersimilar foundation is a poor insulator, some means mustbe considered prior to the application of the lining eitherto override the heat sink or to distribute the heatuniformly. This can be accomplished in several ways:

(a) with the use of properly sized heaters;

(b) placing the tank on a concrete pad topped offwith a 4-in.(10-cm) layer of vermiculite concrete;

(c) insulating with a high compressive strengthstructural grade insulation between the tank bottomand foundation;

(d) installing an internal temporary false bottomapproximately 5 ft (1.5 m) above the floor of the tankprior to the final high temperature bake; or

(e) other suitable means that will practically andeffectively ensure a properly cured lining on the tankfloor.

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Section 4: Surface Finish Requirements

4.1 Sharp edges and fillets shall be ground to a smoothradius of at least 1/8 in. (3 mm); 1/4 in. (6 mm) is pre-ferred.

4.2 Tank surfaces to be lined shall contain no wax orgrease pencil marks, gouges, handling marks, deepscratches, metal stamp marks, slivered steel, or othersurface flaws. The flaws shall be repaired by solventcleaning, welding, or grinding, as appropriate.

4.3 All rough welds shall be ground to remove sharpedges, undercuts, pinholes, and other such irregularities(Figure 2, Appendix A). Chipping can be used to removesharp edges if followed by grinding. (See Appendix C forwritten and graphic descriptions of five different degreesof surface finishing of welds that may be specifiedpreparatory to the lining of tanks and vessels.)

4.3.1 The amount of grinding performed shall bejudicious and performed only to the extent necessaryto prepare the weld surface and surrounding metal

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RP0178-95

surfaces in accordance with the specification. Over-grinding, which would result in decreasing the wallthickness or the integrity of the weld beyond the limi-tations imposed by good welding practices, appli-cable welding codes, pressure vessel ratings, etc.,shall be avoided.

4.4 Automatic machine welds may be acceptable asdictated by the specifications for film continuity.

4.5 All weld spatter must be removed. Chipping may beused if followed by grinding or use of abrasive disc.

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4.6 The use of an anti-spatter coating applied adjacent tothe weld area prior to welding is suggested. The use ofsilicone, oil, or any other anti-spatter materials that wouldnot be readily removed by abrasive blasting shall beavoided.

4.7 The fabricator shall avoid the use of oils or otherforeign material for checking weld continuity that wouldleave a contaminating residue not easily removed byabrasive blasting.

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APPENDIX A—Fabrication Details, Surface Finish Requirements, and Proper Design Considerationsfor Metal Tanks and Vessels to Be Lined for Immersion

FIGURE A1 - All construction involving pockets or crevices that will not drain or that cannot be properly sandblasted andlined shall be avoided.

DO DON’T

FIGURE A2 - All joints shall be continuous full penetration weld. In tanks that require a 100% holiday-free lining, all weldsmust be smooth with no porosity, holes, high spots, lumps, or pockets. Grinding is required to eliminate porosity, sharpedges, and high spots. The use of weld metal to fill in undercuts, etc., is required for severe service conditions and/or highbake linings. Compatible caulking materials may be used for filling in mild service such as dry bulk storage.

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FIGURE A3 - All weld spatter shall be removed.

FIGURE A4 - The outlets shall be flanged or pad type rather than threaded. Within pressure limitations, slip-on flanges arepreferred as the inside surface of the attaching weld is readily available for radiusing and grinding. If operating pressuredictates the use of weld neck flanges, the inside surface of the attaching weld is in the throat of the nozzle making repair ofsurface irregularities by grinding rather difficult.

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FIGURE A5 - Butt welding should be utilized rather than lap welding or riveted construction.

FIGURE A6 - Stiffening members should be on the outside of the vessel or tank.

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FIGURE A7 - Roof to Shell Joint. Eliminate crevice and lap weld at roof to shell interface in a non-pressure vessel.

FIGURE A8 - Dissimilar metal (galvanic) corrosion will occur where, for example, an alloy is used to replace the steel bottomof a tank, or similar circumstances when alloy appurtenances must be a part of the construction of the vessel. If a lining isthen applied to the steel and several inches (usually 6 to 24 in. [15 to 61 cm]) onto the alloy, any discontinuity in the liningwill expose a small anode surface. Once corrosion starts, it progresses rapidly because of the large exposed alloy cathodicarea to the much smaller anodic area. Without the lining, galvanic corrosion will cause the steel to corrode at the weld area,but at a much slower rate. The recommended practice is to line completely the alloy as well as the steel, thereby eliminatingthe possible occurrence of a large cathode to small anode surface.

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FIGURE A9 - A technique (detail of fabrication) to allow for good continuity of lining application for inaccessible areas suchas in multicompartment tanks.

FIGURE A10 - Minimum 2 in. (5 cm) diameter nozzle required for most thin film linings. Thicker film linings may require alarger diameter nozzle. This diagram also illustrates suggested construction where a threaded connection is required in atank that requires a holiday-free lining.

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APPENDIX B—Suggested Responsibilities

This section recommends responsibilities that should beassigned to the purchaser, designer, fabricator, liningapplicator, and inspector in order to obtain a properlydesigned and fabricated tank for interior lining.

B.1 Joint Responsibilities

B.1.1 The purchaser, designer, fabricator, inspec-tor(s), and applicator should review and agree to therequirements involved before contractual agreementsare made.

B.1.2 The purchaser, in agreement with the fabri-cator and lining applicator, should assign respon-sibility for inspection of fabrication, surface finish,and lining application, and such responsibility shouldbe defined in all contracts.

B.2 Responsibilities of the Purchaser (Owner or User)

B.2.1 The purchaser should be responsible for speci-fying and/or approving the detail requirements fordesign, fabrication, and surface finish to all partiesconcerned.

B.2.1.1 The detailed requirements should befully described in writing and include drawings ofthe tank to be fabricated and lined and servicerequirements.

B.2.1.2 The purchaser should advise thedesigner, fabricator, lining applicator, and allinspectors of the detailed requirements, includ-ing time schedules, inspection and acceptablerequirements, in writing.

B.3 Responsibilities of the Designer

B.3.1 The designer should be responsible for in-cluding the required fabrication and surface detailson all sketches and drawings related to the tank.

B.4 Responsibilities of the Fabricator

B.4.1 The fabricator should be responsible for adher-ing to the fabrication and surface finish details shownon the working drawings and described in the tankspecifications.

B.4.2 Responsibility for additional welding, grinding,or surface finishing that may be revealed by thesurface preparation for lining, plus any subsequentreblasting, must be defined in the lining contract.

B.4.3 The fabricator, when checking the quality ofthe weld, shall use only those materials that can bereadily and thoroughly removed by the fabricatorafter the completion of the inspection procedure.

B.5 Responsibilities of the Lining Applicator

B.5.1 Responsibilities for additional welding, grind-ing, or surface finishing that may be revealed by thesurface preparation for lining, plus any subsequentreblasting, must be defined in the lining contract.

B.6 Responsibilities of the Inspector(s)

B.6.1 A qualified inspector should be responsible forthe verification of fulfillment of design, fabrication,and surface finish requirements.

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RP0178-95

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e in

tegr

ity o

f the

wel

ds.

The

"as

is"

orig

inal

w

eld

is n

ot a

typ

ical

wel

d; it

is o

nly

inte

nded

to

illus

trat

e de

fect

s in

wel

ds t

hat

mus

t be

cor

rect

ed p

rior

to c

oatin

g an

d lin

ing.

G

ood

wel

ding

pra

ctic

es a

nd w

eldi

ng c

odes

gov

ern

the

inte

grity

of t

he w

eld;

this

sta

ndar

d on

ly a

ddre

sses

sur

face

pre

para

tion

of th

e w

elds

for

the

purp

ose

of c

oatin

g an

d lin

ing

for

imm

ersi

on s

ervi

ce.

(2)

Abr

asiv

e bl

astin

g in

pre

para

tion

for

coat

ing

may

rev

eal

addi

tiona

l po

rosi

ty a

nd u

nder

cutti

ng.

Som

e ap

plic

ator

s re

ques

t th

e fa

bric

ator

to

blas

t th

e w

elds

to

reve

al t

hese

im

perf

ectio

ns p

rior

to r

eque

stin

g in

spec

tion

of th

e gr

indi

ng b

y th

e lin

ing

appl

icat

or.

Res

pons

ibili

ty fo

r re

pair

of im

perf

ectio

ns s

o re

veal

ed s

houl

d be

res

olve

d in

the

pre-

job

conf

eren

ce.

The

vis

ual c

ompa

rato

r m

entio

ned

in A

ppen

dix

C is

a m

old

ed p

last

ic r

eplic

a th

at il

lust

rate

s va

rious

deg

rees

of

surf

ace

finis

hing

for

wel

ds p

rior

to c

oatin

g or

lini

ng.

Ful

l-sea

m w

elds

, sk

ip w

elds

, but

t wel

ds, l

ap w

elds

, and

oth

ers

are

depi

cted

. F

or m

ore

info

rmat

ion

cont

act t

he N

AC

E M

embe

rshi

p S

ervi

ces

Dep

artm

ent,

P. O

. Box

218

340

, Hou

ston

, TX

772

18-8

340.

Min

or

impe

rfect

ions

su

ch

as

poro

sity

and

und

ercu

tting

exi

st.

Wel

d sp

atte

r is

rem

oved

; wel

ds

are

then

gr

ound

sm

ooth

and

bl

ende

d in

to th

e pl

ate

surf

aces

.

Min

or

impe

rfect

ions

su

ch

as

poro

sity

and

und

ercu

tting

exi

st.

Wel

d sp

atte

r is

rem

oved

; wel

ds

are

then

gr

ound

sm

ooth

and

bl

ende

d in

to th

e pl

ate

surf

aces

.

Min

or

impe

rfect

ions

su

ch

as

poro

sity

and

und

ercu

tting

exi

st.

Wel

d sp

atte

r is

rem

oved

; wel

ds

are

then

gr

ound

sm

ooth

and

bl

ende

d in

to th

e pl

ate

surf

aces

.

Gro

und

smoo

th

and

blen

ded.

(2)

Sha

rp p

roje

ctio

ns o

n th

e w

eld

bead

, sla

g, a

nd w

eld

spat

ter

are

rem

oved

.

Sha

rp p

roje

ctio

ns o

n th

e w

eld

bead

, sla

g, a

nd w

eld

spat

ter

are

rem

oved

.

Sha

rp p

roje

ctio

ns o

n th

e w

eld

bead

, sla

g, a

nd w

eld

spat

ter

are

rem

oved

.

10 NACE International