Download Sspc-sp 7/Nace No. 4 September 1, 2000 PDF

TitleSspc-sp 7/Nace No. 4 September 1, 2000
TagsCorrosion Specification (Technical Standard) Welding Abrasive Rust
File Size44.7 KB
Total Pages5
Document Text Contents
Page 1

SSPC-SP 7/NACE No. 4
September 1, 2000

65

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This SSPC: The Society for Protective Coatings and
NACE International standard represents a consensus of
those individual members who have reviewed this docu-
ment, its scope and provisions. Its acceptance does not in
any respect preclude anyone, having 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 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 product covered by Letters Patent, or as
indemnifying or protecting anyone against liability for in-
fringement of Letters Patent. This standard represents
minimum requirements and should in no way be interpreted
as a restriction on the use of better procedures or materials.
Neither is this standard intended to apply in all cases
relating to the subject. Unpredictable circumstances may
negate the usefulness of this standard in specific instances.
SSPC and NACE assume no responsibility for the interpre-
tation or use of this standard by other parties and accept
responsibility for only those official interpretations issued by
SSPC or NACE in accordance with their respective govern-
ing procedures and policies, which preclude the issuance of
interpretations by individual volunteers.

Users of this standard are responsible for reviewing
appropriate health, safety, and regulatory documents and
for determining their applicability in relation to this standard
prior to its use. This SSPC/NACE standard may not neces-
sarily address all potential health and safety problems or
environmental hazards associated with the use of materials,
equipment and/or operations detailed or referred to within
this standard. Users of this standard are also responsible for
establishing appropriate health, safety, and environmental
protection practices, in consultation with appropriate regu-
latory authorities, if necessary, to achieve compliance with
any existing applicable regulatory requirements prior to the
use of this standard.

CAUTIONARY NOTICE: SSPC/NACE standards are
subject to periodic review and may be revised or withdrawn
at any time without prior notice. SSPC and NACE require
that action be taken to reaffirm, revise, or withdraw this
standard no later than five years from the date of initial
publication. The user is cautioned to obtain the latest
edition. Purchasers may receive current information on all
standards and other publications by contacting the organi-
zations at the addresses below:

©NACE International
P.O. Box 218340
Houston, TX 77218-8340
(telephone +1 281/228-6200)

©SSPC: The Society for Protective Coatings
40 24th Street, Sixth Floor
Pittsburgh, PA 15222
(telephone +1 412/281-2331)


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This joint standard covers the use of blast cleaning
abrasives to achieve a defined degree of cleaning of steel
surfaces prior to the application of a protective coating or
lining system. This standard is intended for use by coating
or lining specifiers, applicators, inspectors, or others whose
responsibility it may be to define a standard degree of
surface cleanliness.

The focus of this standard is brush-off blast cleaning.
White metal blast cleaning, near-white blast cleaning, com-
mercial blast cleaning, and industrial blast cleaning are
addressed in separate standards.

Brush-off blast cleaning provides a lesser degree of
cleaning than industrial blast cleaning (SSPC-SP 14/NACE
No. 8). The difference between an industrial blast and a
brush-off blast is that the objective of a brush-off blast is to
allow as much of an existing coating to remain as possible,
and to roughen the surface prior to coating application while
the purpose of the industrial blast is to remove most of the
coating, mill scale and rust, when the extra effort required to
remove every trace of these is determined to be unwar-
ranted.

This joint standard was prepared by the SSPC/NACE
Task Group A on Surface Preparation by Abrasive Blast
Cleaning. This joint Task Group includes members of both
the SSPC Surface Preparation Committee and the NACE
Unit Committee T-6G on Surface Preparation.

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"�" This joint standard covers the requirements for
brush-off blast cleaning of unpainted or painted steel sur-
faces by the use of abrasives. These requirements include
the end condition of the surface and materials and proce-
dures necessary to achieve and verify the end condition.

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SSPC-SP 7/NACE No. 4
September 1, 2000

66

"�$� This joint standard allows tightly adherent rust, mill
scale and/or old coating to remain on the surface.

"�% The mandatory requirements are described in Sec-
tions 1 to 9 as follows:

Section 1 General
Section 2 Definitions
Section 3 References
Section 4 Procedures Before Blast Cleaning
Section 5 Blast Cleaning Methods and Operation
Section 6 Blast Cleaning Abrasives
Section 7 Procedures Following Blast Cleaning and

Immediately Prior to Coating
Section 8 Inspection
Section 9 Safety and Environmental Requirements

NOTE: Section 10, “Comments” and Appendix A, “Explana-
tory Notes” are not mandatory requirements of this stan-
dard.

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$�" A brush-off blast cleaned surface, when viewed
without magnification, shall be free of all visible oil, grease,
dirt, dust, loose mill scale, loose rust, and loose coating.
Tightly adherent mill scale, rust, and coating may remain on
the surface. Mill scale, rust, and coating are considered
tightly adherent if they cannot be removed by lifting with a
dull putty knife after abrasive blast cleaning has been
performed.

$�$ The entire surface shall be subjected to the abrasive
blast. The remaining mill scale, rust, or coating shall be tight.
Flecks of the underlying steel need not be exposed when-
ever the original substrate consists of intact coating.

$�% When a coating is specified, the surface shall be
roughened to a degree suitable for the specified coating
system.

$�� Immediately prior to coating application, the entire
surface shall comply with the degree of cleaning as speci-
fied herein.

$�’ Visual standards or comparators may be specified
to supplement the written definition. In any dispute, the
written standards shall take precedence over visual stan-
dards and comparators. Additional information on visual
standards is available in Section A.4 of Appendix A.

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%�" The documents referenced in this standard are
listed in Section 3.4.

%�$ The latest issue, revision, or amendment of the
referenced standards in effect on the date of invitation to bid
shall govern unless otherwise specified.

%�% If there is a conflict between the requirements of any
of the cited reference standards and this standard, the
requirements of this standard shall prevail.

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���" Mineral and Slag Abrasives
���$ Cleanliness of Recycled Ferrous Metallic

Abrasives
���% Newly Manufactured or Re-Manufactured

Steel Abrasives
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�% A Guide to Safety in Paint Application
���" Solvent Cleaning
.,��"�/0 Visual Standard for Abrasive Blast Cleaned

Steel

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��" Before blast cleaning, visible deposits of oil, grease,
or other contaminants shall be removed in accordance with
SSPC-SP 1 or other agreed upon methods.

��$ Before blast cleaning, surface imperfections such
as sharp fins, sharp edges, weld spatter, or burning slag
should be removed from the surface to the extent required
by the procurement documents (project specification). Ad-
ditional information on surface imperfections is available in
Section A.5 of Appendix A.

��% If a visual standard or comparator is specified to
supplement the written standard, the condition of the steel
prior to blast cleaning should be determined before the
blasting commences. Additional information on visual stan-
dards and comparators is available in Section A.4 of Appen-
dix A.

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’�"� Clean, dry compressed air shall be used for nozzle
blasting. Moisture separators, oil separators, traps, or other
equipment may be necessary to achieve this requirement.

’�$ Any of the following methods of surface preparation
may be used to achieve a brush-off blast cleaned surface:

’�$�" Dry abrasive blasting using compressed air, blast
nozzles, and abrasive.

’�$�$� Dry abrasive blasting using a closed-cycle, recir-
culating abrasive system with compressed air, blast nozzle,

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SSPC-SP 7/NACE No. 4
September 1, 2000

67

and abrasive, with or without vacuum for dust and abrasive
recovery.

’�$�% Dry abrasive blasting using a closed cycle,
recirculating abrasive system with centrifugal wheels and
abrasive.

’�%� Other methods of surface preparation (such as wet
abrasive blasting) may be used to achieve a brush-off blast
cleaned surface by mutual agreement between those re-
sponsible for performing the work and those responsible for
establishing the requirements. NOTE: Information on the
use of inhibitors to prevent the formation of rust immediately
after wet blast cleaning is contained in Section A.9 of
Appendix A.

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2�"� The selection of abrasive size and type shall be
based on the type, grade, and surface condition of the steel
to be cleaned, type of blast cleaning system employed, the
finished surface to be produced (cleanliness and rough-
ness), and whether the abrasive will be recycled.

2�$ The cleanliness and size of recycled abrasives shall
be maintained to ensure compliance with this specification.

2�% The blast cleaning abrasive shall be dry and free
of oil, grease, and other contaminants as determined by the
test methods found in SSPC-AB 1, AB 2 and AB 3.

2�� Any limitations on the use of specific abrasives, the
quantity of contaminants, or the degree of allowable embed-
ment shall be included in the procurement documents (project
specification) covering the work, because abrasive embed-
ment and abrasives containing contaminants may not be
acceptable for some service requirements. NOTE: Addi-
tional information on abrasive selection is given in Section
A.2 of Appendix A.

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��" Visible deposits of oil, grease, or other contami-
nants shall be removed according to SSPC-SP 1 or another
method agreed upon by those parties responsible for estab-
lishing the requirements and those responsible for perform-
ing the work.

��$� Dust and loose residues shall be removed from
prepared surfaces by brushing, blowing off with clean, dry
air, vacuum cleaning, or other methods agreed upon by
those responsible for establishing the requirements and
those responsible for performing the work. NOTE: The
presence of toxic metals in the abrasives or paint being
removed may place restrictions on the methods of cleaning

permitted. The method chosen shall comply with all appli-
cable regulations. Moisture separators, oil separators, traps,
or other equipment may be necessary to achieve clean, dry
air.

��%� After blast cleaning, surface imperfections that
remain (e.g., sharp fins, sharp edges, weld spatter, burning
slag, scabs, slivers, etc.) shall be removed to the extent
required in the procurement documents (project specifica-
tion). Any damage to the surface profile resulting from the
removal of surface imperfections shall be corrected to meet
the requirements of Section 2.4. NOTE: Additional infor-
mation on surface imperfections is contained in Section A.5
of Appendix A.

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/�" Work and materials supplied under this standard
are subject to inspection by a representative of those re-
sponsible for establishing the requirements. Materials and
work areas shall be accessible to the inspector. The proce-
dures and times of inspection shall be as agreed upon by
those responsible for establishing the requirements and
those responsible for performing the work.

/�$� Conditions not complying with this standard shall be
corrected. In the case of a dispute, an arbitration or settle-
ment procedure established in the procurement documents
(project specification) shall be followed. If no arbitration or
settlement procedure is established, then a procedure mu-
tually agreeable to purchaser and supplier shall be used.

/�% The procurement documents (project specification)
should establish the responsibility for inspection and for any
required affidavit certifying compliance with the specifica-
tion.

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0�" Because abrasive blast cleaning is a hazardous
operation, all work shall be conducted in compliance with
applicable occupational and environmental health and safety
rules and regulations. NOTE: SSPC-PA Guide 3, “A Guide
to Safety in Paint Application,” addresses safety concerns
for coating work.

"8�����55
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"8�" Additional information and data relative to this
standard are contained in Appendix A. Detailed information
and data are presented in a separate document, SSPC-SP
COM, “Surface Preparation Commentary.” The recommen-
dations contained in Appendix A and SSPC-SP COM are
believed to represent good practice, but are not to be
considered requirements of the standard. The sections of
SSPC-SP COM that discuss subjects related to brush-off

Page 4

SSPC-SP 7/NACE No. 4
September 1, 2000

68

blast cleaning are listed below.

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Abrasive Selection ................................. 6
Film Thickness ..................................... 10
Wet Abrasive Blast Cleaning ............. 8.2
Maintenance Repainting .................... 4.2
Rust-back (Re-rusting) ....................... 8.3
Surface Profile .................................... 6.2
Visual Standards ................................. 11
Weld Spatter ................................... 4.4.1

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��"�� ;��*,��)�Brush-off blast cleaning (SSPC-SP 7/
NACE No. 4), provides a lesser degree of cleaning than
industrial blast cleaning (SSPC-SP 14/NACE No. 8). It
should be used when the service environment is mild enough
to permit tight mill scale, coating, rust, and other foreign
matter to remain on the surface. The primary functions of
blast cleaning before coating are (a) to remove material from
the surface that can cause early failure of the coating and (b)
to obtain a suitable surface roughness and to enhance the
adhesion of the new coating system. The hierarchy of
blasting standards is as follows: white metal blast cleaning,
near-white blast cleaning, commercial blast cleaning, indus-
trial blast cleaning, and brush-off blast cleaning.

��$� ���(��,.����<��*,��) Types of metallic and
non-metallic abrasives are discussed in the Surface Prepa-
ration Commentary (SSPC-SP COM). It is important to
recognize that blasting abrasives may become embedded in
or leave residues on the surface of the steel during prepa-
ration. While normally such embedment or residues are not
detrimental, care should be taken to ensure that the abra-
sive is free from detrimental amounts of water-soluble,
solvent-soluble, acid-soluble, or other soluble contaminants
(particularly if the prepared steel is to be used in an immer-
sion environment). Criteria for selecting and evaluating
abrasives are given in SSPC-AB 1, “Mineral and Slag
Abrasives,” SSPC-AB 2, “Cleanliness of Recycled Ferrous
Metallic Abrasives,” and SSPC-AB 3, “Newly Manufactured
or Re-Manufactured Steel Abrasives.”

��%���;( �����(� ,<�)� Surface profile is the rough-
ness of the surface which results from abrasive blast clean-
ing. The profile depth (or height) is dependent upon the size,
shape, type, and hardness of the abrasive, particle velocity
and angle of impact, hardness of the surface, amount of
recycling, and the proper maintenance of working mixtures
of grit and/or shot.

The allowable minimum/maximum height of profile is
usually dependent upon the thickness of the coating to be

applied. Large particle sized abrasives (particularly metal-
lic) can produce a profile that may be too deep to be
adequately covered by a single thin film coat. Accordingly,
it is recommended that the use of larger abrasives be
avoided in these cases. However, larger abrasives may be
needed for thick film coatings or to facilitate removal of thick
coatings, heavy mill scale, or rust. If control of profile
(minimum/maximum) is deemed to be significant to coating
performance, it should be addressed in the procurement
documents (project specification). Typical profile heights
achieved with commercial abrasive media are shown in
Table 5 of the Surface Preparation Commentary (SSPC-SP
COM). Surface profile should be measured in accordance
with NACE Standard RP0287 (latest edition), “Field Mea-
surement of Surface Profile of Abrasive Blast Cleaned Steel
Surfaces Using Replica Tape, “ or ASTM(1) D 4417 (latest
edition), “Test Method for Field Measurement of Surface
Profile of Blast Cleaned Steel.”

�����.,�;�<��*��&�(&�)� SSPC-VIS 1-89 (Visual
Standard for Abrasive Blast Cleaned Steel) provides color
photographs for the various grades of surface preparation
as a function of the initial condition of the steel. The series
A-SP 7, B-SP 7, C-SP 7 and D-SP 7 depict surfaces cleaned
to brush-off blast grade. Other available visual standards
are described in Section 11 of SSPC-SP COM.

��’���;( ����,1��( ��*,���) Surface imperfec-
tions can cause premature failure when the service is
severe. Coatings tend to pull away from sharp edges and
projections, leaving little or no coating to protect the under-
lying steel. Other features that are difficult to properly cover
and protect include crevices, weld porosities, laminations,
etc. The high cost of the methods to remedy surface
imperfections requires weighing the benefits of edge round-
ing, weld spatter removal, etc., versus a potential coating
failure.

Poorly adhering contaminants, such as weld slag resi-
dues, loose weld spatter, and some minor surface lamina-
tions may be removed during the blast cleaning operation.
Other surface defects (steel laminations, weld porosities, or
deep corrosion pits) may not be evident until the surface
preparation has been completed. Therefore, proper plan-
ning for such surface repair work is essential because the
timing of the repairs may occur before, during, or after the
blast cleaning operation. Section 4.4 of SSPC-SP COM and
NACE Standard RP0178 (latest edition), “Fabrication De-
tails, Surface Finish Requirements, and Proper Design
Considerations for Tanks and Vessels to be Lined for Im-
mersion Service” contain additional information on surface
imperfections.

��2���+�1,��<����*�1,��*,��) Steel contami-
nated with soluble salts (e.g., chlorides and sulfates) devel-
ops rust-back rapidly at intermediate and high humidities.

(1) ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-

2959.

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