1. GENERAL
This specification defines minimum quality and technical
standards governing design, manufacturing and supply of aluminum bracelet
anodes used with offshore pipelines.
This specification is to be used in conjunction with the following
documents:
·
Basis of Design 84506-60-30-2L-060
·
General Specification
84506-60-00-2L-000 - Definitions and Specification Directory
·
General Specification
84506-60-00-2L-010 - Quality Assurance / Quality Control
·
NACE RP-0387-90 - Metallurgical and
Inspection Requirements for Cast Sacrificial Anodes for Offshore Applications
·
NACE RP-0492-99 - Acceptance Criteria
for Cracks in Cast Anodic Materials
·
NACE RP-06-75 - Control of External
Corrosion on Offshore Steel Pipelines
·
ASTM A283 - Standard Specification for
Low and Intermediate Tensile Strength Carbon Steel Plates
·
BS EN 10204 - Inspection Documents for the Delivery of Dry Metallic Products.
·
AWS D.1.1 - Structural Welding
·
SSPC-SP-10 - Near White Blast Cleaning
·
DNV RP B401 - Cathodic Protection
Design
2. ANODE DESIGN
2.1 CONTRACTOR
shall be responsible for aluminum bracelet anode design, in accordance with
NACE RP-06-75 and DNV RP B401, and as detailed below:
2.2 CONTRACTOR
shall submit detailed fabrication drawings of each anode design for COMPANY
approval.
Table 2.1 – Anode Design Requirements
|
Service Life
|
As per Basis of Design
|
|
Anode Type and Material
|
Bracelet / Galvalum III or COMPANY-approved equal
|
|
Anode Utilization Factor
|
0.80
|
|
Anode Output Capacity @ 10°C
|
2500 Ah/kg (seawater) / 2000 Ah/kg (buried)
|
|
Driving
Potential
w.r.t. Ag/Ag/Cl |
-1.05V (seawater)
-0.95V (buried)
|
2.3 Bracelet
anodes shall be sized to form a snug fit on the anti-corrosion coating.
2.4 Each
bracelet half-shell shall be capable of being attached to its partner half
shell by welding together the protruding tabs of the anode insert material.
3. MATERIALS
3.1 Anode Material
3.1.1 The
sacrificial anode material shall be an aluminium-zinc-indium type alloy, which
shall exhibit the electrochemical properties defined in Table 2-1.
3.1.2 Test
data demonstrating the performance of the anode material in terms of
electrochemical efficiency and closed circuit potential shall be supplied for
COMPANY approval. The data shall show
performance at a range of temperatures between 5°C and 65°C in both seawater and saline mud.
3.2 Insert Material
3.2.1 All core steel
used in anode bracelet construction shall be ASTM A283 Grade C or COMPANY
approved equal, and shall be welded by welders qualified to AWS D.1.1. using
COMPANY-approved welding procedure specifications.
3.2.2 The
carbon equivalent (CE) of the insert material shall not exceed 0.40% as
determined by the following equation based on ladle analyses:
Each element symbol represents its percentage content by
weight.
Mill certificates for steel insert materials shall be
supplied in accordance with BS EN 10204 Type 3.1(b).
3.3 Cable
3.3.1 Each anode
bracelet half shell shall include two (2) insulated bonding cables welded to
exposed steel core flat bar(s), using a Cadweld F-33 alloy Thermit charge, or
COMPANY approved equal. Each electrical
lead shall have a conducting area equal to four (4) American Wire Gage (AWG)
standard insulated copper wire and length sufficient for the free end to be
attached to the linepipe in the center of the gap between the anode half
shells. The connections shall be
carefully cleaned and protected against all damage during handling and
shipping.
3.3.2 Technicians
applying cad welds shall be pre-qualified by performing at least 3 attachments
for destructive testing. Two joints
shall be destructively tested for strength.
The third joint shall be cross-sectioned for fusion evaluation.
3.3.3 Each
of the bracelet half shell bonding cables at each anode assembly shall be
connected separately to the pipeline, connected in the center of each gap.
4. MANUFACTURING
4.1 CONTRACTOR
shall provide, for COMPANY approval, a minimum 30 days prior to start of
production, a project quality plan, manufacturing and test/inspection procedures
covering steel core fabrication, design and fabrication of casting and cooling
molds, alloy melting and casting and bonding cable installation.
4.2 As
a minimum requirement, casting and cooling procedures shall specifically
address:
·
Controlling the pouring temperature for
the chosen alloy.
·
Continuous pouring of the molten metal
into the mould to prevent molten alloys from stratifying on cooling.
·
Cooling/time ratios.
·
Cooling procedures.
·
Manufacturing design to produce anodes
with minimal susceptibility to shrinkage cracks in the thin area over the anode
core.
4.3 COMPANY
has the right to require pre qualification of the manufacturing process prior
to full production. This may include, but not be limited to, manufacture of
casting and cooling molds, steel core fabrication and anode manufacture.
4.4 Anode
casting molds shall prevent excessive distortion during the cooling process
after casting.
4.5 Manufacturing
procedures shall include a dimensional core check, to ensure suitable
incorporation into the casting. Bare
steel core dimensions and structure shall be COMPANY approved prior to
beginning the Work. Core reinforcement,
connecting bar dimensions and position shall be COMPANY approved prior to start
of anode casting.
4.6 Cores
shall be abrasive cleaned to standard SSPC-SP-10 and shall be incorporated into
the anode casting within twelve (12) hours of cleaning. Cores shall be stored in a clean, dry
environment after blasting. Each core
shall be examined for cleanliness immediately prior to casting and any core
contaminated with rust, dirt, mill scale, grease or other surface imperfection
shall be re-cleaned using the method described.
4.7 Net
weight of each anode bracelet, defined as the minimum acceptable weight of the
bracelet excluding the steel core, shall be in accordance with that specified
in the Purchase Order, and shall be COMPANY approved.
4.8 Each
anode assembly shall be coated with coal tar epoxy on the inside surface and
the edges. The minimum coating thickness
shall be 300 microns.
5. INSPECTION AND TESTING
5.1 Bracelet
anodes shall be inspected and tested in accordance with NACE RP-0387-90 and as
detailed below. COMPANY may witness all
aluminum bracelet anodes manufacturing and testing phases at CONTRACTOR works. CONTRACTOR shall provide all reasonable
facilities to COMPANY to ensure anodes are manufactured in accordance with this
specification. All inspections and tests
are to be made prior to shipment from CONTRACTOR works.
5.2 CONTRACTOR
shall furnish all material, equipment and qualified personnel to perform the
examinations and testing specified herein.
Any inspection provided by COMPANY shall not relieve CONTRACTOR of its
responsibility to ensure quality control.
5.3 In
addition to 5.2, CONTRACTOR shall provide continuous Third Party monitoring of
all aspects of the casting operation to ensure adherence to manufacturing,
inspection and testing requirements.
5.4 Welded
steel cores shall be subject to ten percent (10%) random Magnetic Particle
Inspection (MPI).
5.5 Mill
certificates shall be provided to COMPANY for each alloy melt. These certificates shall indicate:
·
Name of manufacturer
·
Alloy metallurgical composition using
spark emission spectography
·
Net and gross weight of each anode
·
Dimensions of each anode
5.6 Quality
control samples shall be taken at the start and finish of melts producing more
than four (4) bracelets, otherwise, one (1) sample is required. Sample Q.C. certificates shall be provided to
COMPANY for approval.
5.7 Efficiency
and solution potential test results shall be furnished for each production lot
to confirm minimum efficiency and potential requirements have been met. Tests shall include, but not be limited to,
closed circuit potential and current capacity measurements. Efficiency shall be determined by the
twenty-four (24) hour gas evolution test method, except that for at least ten
percent (10%) of the samples the test shall be continued for twenty-eight (28)
days and efficiency determined by weight loss.
Testing shall be done by a COMPANY approved independent testing
laboratory.
5.8 CONTRACTOR
shall perform dimensional inspection of each bracelet anode segment, and the
following dimensions shall be as shown on approved shop drawings, with
tolerances of:
·
Pipe, external anti-corrosion coating
and concrete thickness
·
Inner Diameter (-0.0 mm, +1.5% of anode
ID)
·
Outer Diameter (+/-5.0 mm)
·
Thickness (+/-5.0 mm)
·
Length (+/-10.0 mm)
·
Core Position (+/-10.0 mm)
5.9 After dimensional inspection and prior to
inspection for allowable defects, all bracelet anode segments shall be trial
fitted, in connected pairs, to a pipeline joint.
5.10 CONTRACTOR
shall weigh all anodes using a method accurate to plus or minus one half
percent (+/- 0.5%) of gross weight. Each
individual anode net weight shall be within plus or minus three percent (+/-
3%) of the weight shown on the CONTRACTOR shop drawings.
5.11 Net
weight of all anode material shall be established by multiplying average
individual anode net weights by total number of anodes, and shall be within
minus zero, plus two percent (- 0%, + 2%) of the specified total net weight.
5.12 CONTRACTOR
shall perform one hundred percent (100%) radiographic examination on the first
five- (5) anodes of each size or type to establish adherence between core and
anode. Results of the examination shall
be submitted to COMPANY for approval.
5.13 Electrical
continuity tests shall be performed on two percent (2%) of bonding cables,
between free cable end and the anode core.
Electrical resistance shall not exceed 0.01-Ohms. Any bracelet anode where bonding cable
resistance exceeds 0.01-Ohms shall be repaired by removing, cleaning and
reattaching the bonding cable. All other
bonding cables connections made prior to the rejected connection shall be
tested for electrical continuity, until COMPANY is satisfied that bonding
cables are attached correctly.
6. ALLOWABLE DEFECTS
6.1 Every
bracelet anode segment casting shall be visually inspected for defects, and at
least one (1) in fifty (50) for each size shall be sectioned to show
conformance with this specification.
CONTRACTOR shall replace all sectioned units.
6.2 Shrinkage
cavities greater than ten percent (10%) of nominal anode depth, or 5 mm,
whichever is less, shall be rejected.
6.3 Acceptance
criteria for cracks in cast anodic materials shall be in accordance with NACE
RP-0492-99 Section 3 Clause 3.10.
6.4 Craters
exceeding 4 mm in diameter shall be rejected, and no more than ten (10) craters
shall be allowed on the outer surfaces of each anode segment.
6.5 One
(1) in fifty (50) bracelet anode segments shall be sectioned transversely by
single cuts at twenty-five percent (25%) and fifty percent (50%) of nominal
length, to determine the bond between steel core and anode material, location
of the steel core and internal porosity levels.
CONTRACTOR shall reject any sectioned bracelet anode segment where:
·
Surface porosity exceeds four percent
(4%)
·
Combined void length adjacent to the
steel core exceeds five percent (5%)
·
Any individual pore in the outer eighty
percent (80%) of anode material depth exceeds 8 mm in length or 25 mm2
in area
·
Any individual pore in the inner twenty
percent (20%) of anode material depth exceeds 10 mm in length or 64 mm2
in area
6.6 Should
any sectioned bracelet be rejected, CONTRACTOR shall divide that batch of fifty
(50) bracelet anodes segments in batches of ten (10) and section one segment
from each smaller batch. Rejection of
any segment in the smaller batch of ten (10) shall result in rejection of that
entire batch of ten (10).
6.7 Slag
or casting (sand) inclusions shall not be permitted.
6.8 All
welded connections shall be visually inspected for defects, and any defect
disclosed shall be removed and rewelded to COMPANY satisfaction.
7. MARKING
Each anode shall be stamped with the following information:
·
Manufacturer's Mark
·
ADGF Project
·
Cast Number / Melt Number
·
Weight (required gross)
·
Internal Diameter (in SI and Imperial)
8. RECORDS
8.1 All
records shall be fully identified with the specific materials they represent,
and they shall be available for COMPANY examination at the time and place of
inspection, whether at the point of manufacture or distributor's location.
9. QUALITY CONTROL
9.1 CONTRACTOR
shall comply with the requirements of Project Specification for Quality
Assurance and Quality Control 84506-60-00-2L-010.
9.2 CONTRACTOR
shall submit a quality plan detailing the quality control program for COMPANY
review and approval.
9.3 CONTRACTOR
shall supply materials only from manufacturers or sub-contractors that have
been approved by COMPANY.
10. HANDLING, STORING AND SHIPPING
10.1 CONTRACTOR
shall pack and ship anode bracelets or wooden pallets in accordance with
COMPANY approved procedures.
10.2 Procedures
shall address as a minimum, all lifting, handling, storing and shipping
requirements.
10.3 Anodes
shall be stored above ground level and be electrically isolated from the earth,
steel structures, and any other objects that may adversely affect the anodes.
11. DOCUMENTATION
CONTRACTOR shall submit to COMPANY for approval 30 days
prior to commencement of work, a comprehensive package of documents including:
a.
Quality Plan
b.
Manufacturing Procedures
c.
Inspection and Testing Procedures
d.
Acceptance criteria for allowable
defects
e.
Design Calculations
f.
Data Sheets
g.
Shop Drawings
h.
Anode Performance Relative to Temperature
i.
Handling, Shipping and Storage
Procedures
CONTRACTOR shall collate the following data as a minimum and
include in a data book:
a.
Alloy Mill Certificates
b.
Material Test Certificates
c.
Certified NDT Examination Reports
d.
Certified Drawings
e.
Inspection Records
f.
Calibration Certificates
Data book shall be submitted to COMPANY within 28 days of
satisfactory completion of anode manufacturing and testing.
All certificates shall be in the English language and use
metric units of measure. CONTRACTOR and
COMPANY shall visibly sign certificates.
All data to be submitted in bith hard copy and electronic
format.