GB/T 21447-2018 PDF English (GB/T 21447-2008: Older version)
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GB/T 21447-2018: PDF in English (GBT 21447-2018) GB/T 21447-2018
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 75.200
E 98
Replacing GB/T 21447-2008
Specifications for steel pipeline
external corrosion control
ISSUED ON. FEBRUARY 6, 2018
IMPLEMENTED ON. SEPTEMBER 1, 2018
Issued by. General Administration of Quality Supervision, Inspection and
Quarantine of the PRC;
Standardization Administration of the PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Basic provisions ... 8
5 Anticorrosion coating design ... 10
6 Cathodic protection design ... 13
7 Interference mitigation ... 18
8 Construction and acceptance ... 23
9 Operation and maintenance management ... 27
10 Corrosion control records ... 32
Foreword
This Standard is drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 21447-2008 “Specification for external corrosion
control for steel pipeline”. As compared with GB/T 21447-2008, in addition to
editorial modifications, the main technical changes are as follows.
- MODIFY the scope of application of this Standard (SEE Chapter 1);
- ADD 5 terms (SEE 3.1, 3.5, 3.11, 3.12, and 3.13);
- REVISE and ADD environmental corrosivity determination methods and
grading assessment index (SEE 4.3);
- REVISE the general provisions on the design of anticorrosion coatings, and
ADD the provisions on overland buried and underwater pipeline
anticorrosion coatings, overland above-ground pipeline anticorrosion
coatings, and on subsea pipeline anticorrosion coatings (SEE 5.1, 5.2, 5.3,
and 5.4);
- REVISE the criteria for cathodic protection of overland pipelines, and ADD
the cathodic protection content of subsea pipelines (SEE 6.1.2, 6.2);
- ADD general provisions on interference control, and REVISE the judgment
index for AC and DC interference and the assessment index for mitigation
effect (SEE 7.1, 7.2.1, 7.3.1);
- REVISE construction and acceptance content (SEE Chapter 8);
- ADJUST operation and maintenance management content; and ADD
inspection and assessment related content (SEE Chapter 9).
This Standard was proposed by and shall be under the jurisdiction of National
Technical Committee 355 on Oil and Gas of Standardization Administration of
China (SAC/TC 355).
Drafting organizations of this Standard. Daqing Oilfield Engineering Co., Ltd.,
China Petroleum Planning & Engineering Institute, China Petroleum Pipeline
Engineering Corporation, CNOOC Research Institute, CNPC Engineering
Technology R&D Company Limited, Southwest Branch of CNPC Engineering
Design Co., Ltd., PetroChina Natural Gas Pipeline Branch, Institute of Safety,
Environment Protection and Technical Supervision of PetroChina Southwest Oil
and Gasfield Company.
Main drafters of this Standard. Yang Chunming, Zhang Kun, Liu Fang, Huang
Specifications for steel pipeline
external corrosion control
1 Scope
This Standard specifies the minimum requirements for the design, construction,
and management, etc. of steel pipeline (hereinafter known as pipeline for short)
external corrosion control engineering, including basic provisions, anticorrosion
coating design, cathodic protection design, interference mitigation, construction
and acceptance, operation and maintenance management, and other contents.
This Standard is applicable to the external corrosion control of oil, gas, and
water pipelines, which are newly-built, expanded, and re-built overland and
subsea, with conveying medium temperature of less than 100 °C.
2 Normative references
The following documents are indispensable for the application of this document.
For the dated references, only the versions with the dates indicated are
applicable to this document. For the undated references, the latest version
(including all the amendments) are applicable to this document.
GB/T 8923.1 Preparation of steel substrates before application of paints and
related products - Visual assessment of surface cleanliness - Part 1. Rust
grades and preparation grades of uncoated steel substrates and of steel
substrates after overall removal of previous
GB/T 19292.1 Corrosion of metals and alloys - Corrosivity of atmospheres -
Part 1. Classification
GB/T 21246 Measurement method for cathodic protection parameters of
buried steel pipelines
GB/T 21448 Specification of cathodic protection for underground steel
pipelines
GB/T 23257 Polyethylene coating for buried steel pipeline
GB 32167 Oil and gas pipeline integrity management specification
GB/T 50538 Technical standard for anti-corrosion and insulation coating of
buried steel pipeline
GB/T 50698 Standard for AC interference mitigation of buried steel pipelines
GB 50991 Technical standard for DC interference mitigation of buried steel
pipeline
GB/T 51172 Inspection code for in-service oil & gas pipeline
GB/T 35988 Cathodic protection of offshore pipeline in petroleum, natural
gas industries
SY/T 0029 Specification of application for underground steel coupons
SY/T 0087.1 Standard of steel pipeline and tank corrosion assessment -
Steel pipeline external corrosion direct assessment
SY/T 0315 Technological specification of external fusion bonded epoxy
coating for steel pipeline
SY/T 0407 Specification of Steel Surface Preparation Before Application of
Paint
SY/T 0414 Specification of polyolefin tape coating for steel pipeline
SY/T 0447 Standard of coal tar epoxy coating for buried steel pipeline
SY/T 5918 Technical specification for thermal insulation repair of buried steel
pipeline exterior coating
SY/T 6854 Technical standard of liquid epoxy external coating for buried
steel pipeline
SY/T 6878 Cathodic protection of submarine pipelines by galvanic anodes
SY/T 6964 Specification of cathodic protection for petroleum and gas station
SY/T 7036 Specification of external coating for piping and equipment in
petroleum and gas stations
SY/T 7041 Specification of polypropylene coating for steel pipeline
SY/T 7347 Standard of coating and insulation for aboveground oil and gas
pipelines
3 Terms and definitions
The following terms and definitions apply to this document.
3.11 Direct assessment; DA
An integrity assessment method which uses a structured process. That is, by
integrating the physical characteristics of pipeline, the operational record of the
system, or the test, inspection, and assessment results, and other information
of pipeline, a predictive conclusion of pipeline integrity assessment is given.
3.12 Fault
The mechanical damage, uncoated dot on the anticorrosion coating and other
defects of anticorrosion coating.
3.13 Subsea pipeline
INCLUDE risers and pipelines below the water level at the highest tidal level.
4 Basic provisions
4.1 It shall, according to factors such as the expected service life of pipeline,
engineering safety requirements, and economy, carry out pipeline external
corrosion control.
a) Newly-built pipeline. External anticorrosion coating (hereinafter known as
anticorrosion coating) or anticorrosion coating combined with cathodic
protection shall be used. If the investigation indicates that corrosion
control is not required, it may not be used.
b) Buried or underwater pipelines which have been built with anticorrosion
coating and no cathodic protection. If the investigation indicates that
corrosion control needs to be strengthened, cathodic protection shall be
added.
c) Pipelines which have been built without external corrosion control.
Corrosion conditions of the pipeline system shall be detected and
evaluated. The corrosion control measures taken, based on the
assessment results, shall be determined.
4.2 The selection of corrosion control method shall consider the following
factors.
a) Environmental corrosivity;
b) Pipeline characteristics;
c) Operating conditions;
anticorrosion coating, in addition to the factors of 5.1.2, the following factors
shall also be considered.
a) Compatibility with cathodic protection;
b) Soil stress, including the stress caused by thermal-cold cycling;
c) Resistance to mechanical damage in rocky area, trenchless crossing
construction, or under the influence of other external forces;
d) Resistance to impact damage;
e) The effects of the interface between the atmosphere and the soil;
f) Matching with the weight coating of pipeline.
5.2 Anticorrosion coating of buried and underwater pipelines
5.2.1 The anticorrosion coating of buried and underwater pipelines shall have
good resistance to soil stress in addition to the basic properties specified in
5.1.1; and shall be matched with cathodic protection.
5.2.2 When the pipeline is constructed in a low temperature environment, the
anticorrosion coating shall also have good low-temperature construction
property.
5.2.3 For rocky segment pipelines and the pipe sections where the construction
process is likely to cause damage to the anticorrosion coating, it shall take
protective measures. The protective measures include but are not limited to fine
soil backfilling, thickening anticorrosion coating, protective layer of
anticorrosion coating, etc. When choosing a protective layer, the following
factors shall be considered.
a) It shall match the chemical and physical properties of the pipeline
anticorrosion coating;
b) The protective layer shall not adversely affect the effectiveness of cathodic
protection.
5.2.4 For buried and underwater pipeline anticorrosion coating, when selecting
the following external anticorrosion coatings of pipeline, the following standards
shall be implemented.
a) The extruded polyethylene anticorrosion coating shall comply with the
provisions of GB/T 23257;
b) The extruded polypropylene anticorrosion coating shall comply with the
6 Cathodic protection design
6.1 Overland pipeline
6.1.1 General provisions
6.1.1.1 Cathodic protection shall be adopted for buried oil and gas long-
distance pipelines, oil and gas field outward-transmission pipelines, and oil and
gas field internal transmission trunk pipelines. Cathodic protection shall be used
for other buried pipelines.
6.1.1.2 Cathodic protection shall be implemented in conjunction with
anticorrosion coating.
6.1.1.3 The cathodic protection engineering shall be surveyed, designed,
constructed, and put into operation simultaneously with the main engineering.
When the cathodic protection system is not operational within three months of
pipeline burying, temporary cathodic protection measures shall be taken. In a
highly corrosive soil environment, when the pipeline is buried, temporary
cathodic protection measures shall be applied. Temporary cathodic protection
measures shall be maintained until the permanent cathodic protection system
is put into operation. For pipelines affected by DC stray current interference,
cathodic protection (including electrical drainage protection) shall be put into
operation within three months.
6.1.1.4 The cathodic protection of buried or underwater pipelines can be done
by forced current method, galvanic anode protection method, or a combination
of the two methods. It shall be economically and rationally selected according
to factors such as engineering scale, soil environment, and quality of pipeline
anticorrosion coating.
6.1.1.5 When designing, it shall be considered that cathodic protection may be
ineffective or partially ineffective under special conditions such as high
temperature, anticorrosion coating peeling, thermal insulation coating, shielding,
bacterial erosion, and abnormal electrolyte contamination.
6.1.1.6 The protected pipeline shall be electrically isolated from other metal
structures. When electric isolation is not possible, the cathodic protection
current loss shall be considered.
6.1.1.7 The protection of parallel or cross pipelines shall meet the following
principles.
a) When the parallel pipeline adopts joint cathodic protection, it shall, at the
confluence and other appropriate positions, set the jumper wire. When
c) AC interference mitigation measures and mitigation effects shall meet the
relevant provisions of GB/T 50698.
6.1.2.7 Cathodic protection criteria under DC interference
a) When the pipeline is affected by DC interference, mitigation measures
shall be taken.
b) DC interference mitigation measures and mitigation effects shall meet the
relevant provisions of GB 50991.
6.1.2.8 The cathodic protection effect can also be determined by corrosion
condition check or coupons corrosion rate test method, to assess the
effectiveness of cathodic protection.
a) Corrosion condition check, including appearance check of the protected
pipeline, corrosion type, corrosion product analysis, corrosion depth and
metal wall thickness test, etc. The results obtained shall indicate that the
degree of corrosion does not exceed the limits allowed by the service life
of the protected pipeline.
b) Coupons corrosion rate test. The coupons corrosion rate test results shall
be limited to the allowable range.
6.1.3 The cathodic protection of buried pipelines shall be carried out in
accordance with GB/T 21448. The cathodic protection of buried pipelines in
stations shall be carried out in accordance with SY/T 6964.
6.2 Subsea pipeline
6.2.1 General provisions
6.2.1.1 For subsea pipelines located in full-immersion zone, cathodic protection
system shall be used to provide adequate protection to the pipeline. The
cathodic protection method can use a galvanic anode or an impressed current.
6.2.1.2 The cathodic protection design of the short-distance subsea pipeline or
its branch pipe directly connected to the cathodically-protected overland
pipeline shall be implemented in accordance with GB/T 21448.
6.2.2 The cathodic protection effect of subsea pipelines shall meet the
requirements of Table 6.
7.1.2 In the engineering design of electric power, railway, subway, pipeline, etc.,
the interference effects which the pipeline may be subjected to shall be fully
considered; and the stray current corrosion and the influence on the corrosion
control system which may occur on the pipeline shall be analyzed and
evaluated.
7.1.3 The party of interference source which causes interference to the pipeline
shall, in accordance with the current relevant national standards, adopt
measures to mitigate interference, and shall provide support for investigation,
testing, and protection of pipeline interference.
7.1.4 In the interference area, the interfered party, the party of interference
source, and other relevant parties shall form an anti-interference coordinating
agency, to conduct unified testing and evaluation of the interference, and to
coordinate the design of interference mitigation measures and implement and
manage separately.
7.1.5 When it is confirmed that the pipeline is subjected to interference effect
and damage, mitigation measures appropriate to the degree of interference
shall be taken.
7.1.6 In the same or the same system of pipelines, according to the actual
conditions, one or more mitigation measures may be used.
7.1.7 The pipeline affected by interference can be fitted with coupons, polarized
probe, or resistance probe.
7.2 DC interference
7.2.1 The judgment of DC interference shall comply with the following rules.
a) The newly-built pipeline in the design stage can be judged by the soil DC
potential gradient on both sides of the pipeline. When the soil DC potential
gradient is >0.5 mV/m, it is confirmed that there is DC stray current. When
the soil potential gradient is ≥2.5 mV/m, the possible influence of DC
interference after the pipeline is laid shall be evaluated; and according to
the evaluation results, the interference mitigation measures shall be
preset.
b) The pipeline which has been built shall be judged by the offset value of
pipe-to-soil potential relative to natural potential when there is no cathodic
protection current. When the pipe-to-soil potential at any point is more
than 20 mV of offset in the positive or negative direction with respect to
the natural potential, it shall be confirmed that there is DC interference.
When the pipe-to-soil potential at any point is ≥100 mV of offset in positive
direction with respect to the natural potential, interference mitigation
measures shall be taken in time.
c) For cathodically-protected pipelines which have been put into operation,
when the interference causes the pipeline to fail to meet the protection
criteria, interference mitigation measures shall be taken in time.
d) The form of interference may, according to the degree of interference and
the change of interfered position with time, be determined to be dynamic
or static.
7.2.2 According to the results of investigation and test, interference mitigation
measures such as electrical drainage protection, cathodic protection,
anticorrosion coating repair, equipotential bonding, insulated isolation,
insulation device bridging, and shielding shall be selected for pipeline sides.
The following factors shall be considered in the selection of mitigation measures.
a) The source of interference and the mutual position relationship between
interference source and pipeline;
b) The form and extent of interference;
c) The range of interference and the location of anode zone of pipeline,
cathode zone of pipeline, and alternating zone of pipeline;
d) Environmental factors such as terrain, landform, and soil resistivity around
the pipeline;
e) Insulating property of pipeline anticorrosion coating;
f) Existing interference mitigation measures for pipelines and protective
effects of the interference mitigation measures.
7.2.3 When the adjustment of cathodic protection system of the interfered
pipeline cannot mitigate the interference effects, electrical drainage protection
and other mitigation measures shall be taken.
7.2.4 After the implementation of interference mitigation measures, the
interference mitigation effect assessment test shall be carried out. After the
interference mitigation measures are taken, the following requirements shall be
met.
a) For pipelines and other common protective structures in the interference
mitigation system, the pipe-to-soil potential shall reach the cathodic
protection potential standard or be in or close to the state of not being
interfered with;
b) For pipelines and other common protective structures in the interference
SY/T 0407.
8.2.1.2 When applying on site, the following provisions shall be met.
a) Defects in the anticorrosion coating shall be repaired. The coating material
of pipeline anticorrosion coating repaired mouths and patches and of
connecting device of pipe fittings and pipelines shall be matched with the
previous anticorrosion coating of the pipeline;
b) The bottom of pipe trench shall be flat; and free of stones or other
materials which may damage the anticorrosion coating or cause electric
shielding. Under harsh conditions, liner pipelines or cushioning at the
bottom of the trench shall be considered;
c) When the pipeline is under the trench and backfilled, care shall be taken
to avoid damage to the pipeline anticorrosion coating by trench tools,
stones, etc.;
d) It shall not, around the pipeline, use materials such as rock shields which
may have an electric shielding effect on cathodic protection;
e) For pipelines partly located on the ground, suitable anti-atmospheric
corrosion materials shall be used.
8.2.1.3 The construction and acceptance of buried pipeline anticorrosion
coating shall comply with the relevant provisions of the following standards.
a) Extruded polyethylene anticorrosion coating shall comply with the
provisions of GB/T 23257;
b) Extruded polypropylene anticorrosion coating shall comply with the
provisions of SY/T 7041;
c) Fusion bonded epoxy anticorrosion coating shall comply with the
provisions of SY/T 0315;
d) Polyolefin cold tape anticorrosion coating shall comply with the provisions
of SY/T 0414;
e) Solvent-free liquid epoxy anticorrosion coating shall comply with the
provisions of SY/T 6854;
f) Coal tar epoxy anticorrosion coating shall comply with the provisions of
SY/T 0447.
8.2.1.4 The anticorrosion construction and acceptance of buried insulation
pipelines can be carried out in accordance with the relevant provisions of GB/T
shall be made.
8.3.1.2 The construction and acceptance of galvanic anode shall meet the
following requirements.
a) The layout, location, and number of galvanic anodes shall meet the design
requirements. When non-prepackaged galvanic anodes are used, all
waterproof packaging materials of the galvanic anode shall be removed.
The filling material shall be filled around the anode; the anode shall be
placed in the center of the filling material. The filling material shall be
mixed uniformly and completely coated with the anode. When
prepackaged galvanic anodes are used, the filling materials shall be
packed in sacks or cotton cloth bags and shall not be packed in chemical
fiber bags. The galvanic anode shall be soaked in water after it is in place.
b) When the ribbon galvanic anode is constructed in a low temperature
environment, attention shall be paid to the influence of the low
temperature environment on the mechanical properties of the ribbon
anode.
c) The connection between cable and galvanic anode steel core shall be
welded or copper pipe clamped. The welded joint shall be anticorrosive
and insulated.
8.3.1.3 The construction and acceptance of line cathodic protection shall be
carried out according to GB/T 21448. The construction and acceptance of the
cathodic protection of stations shall be carried out according to SY/T 6964.
8.3.2 Subsea pipeline
8.3.2.1 The galvanic anode and the subsea pipeline can be connected by
thermal-welding, brazing, or welding. The heat introduction of the welding
process shall be controlled. After the anode is installed, the welding heat
affected zone shall be thoroughly cleaned; the exposed steel surface shall be
protected by heat shrinkage tape.
8.3.2.2 For pipelines with concrete weight coating, electric connections
between galvanic anodes and concrete reinforcing ribs shall be avoided.
8.3.2.3 Galvanic anode installation inspection of subsea pipelines shall include
the inspection for weld appearance and electric connection.
8.3.2.4 The construction of cathodic protection of subsea pipelines by galvanic
anodes can be carried out in accordance with the relevant provisions of SY/T
6878.
9.1.1.3 The corrosion defects of the pipe body shall be evaluated. According to
the evaluation results, the repair measures shall be determined, and the defects
shall be repaired in time.
9.1.1.4 After the pipeline leaks due to external corrosion, the corrosion
mechanism shall be analyzed, to determine the cause of the corrosion and take
corresponding countermeasures.
9.1.2 Pipeline inspection
9.1.2.1 The external corrosion inspection of pipeline can be performed by
internal inspection, direct assessment of external corrosion, or other suitable
methods. The internal inspection of pipeline shall be carried out in accordance
with the provisions of GB 32167. The direct assessment of external corrosion
shall be carried out in accordance with the provisions of SY/T 0087.1.
9.1.2.2 After the pipeline is put into production, pipeline baseline inspection
shall be carried out within 3 years. The inspection interval shall be
comprehensively determined based on the results of the last inspection. The
inspection cycle shall be shortened for pipelines with insulation coating.
9.1.2.3 The pipeline management department shall, based on the results of
external corrosion inspection of pipeline, evaluate the effectiveness of the
external corrosion control measures. For the pipe sections where the external
corrosion control measures are ineffective, countermeasures shall be taken in
time.
9.1.3 Anticorrosion coating management
9.1.3.1 Pipeline anticorrosion coating management shall be carried out
combined with the integrity assessment results. When there is an internal
inspection report, the maintenance and management of anticorrosion coating
shall be guided based on the internal inspection results preferentially.
9.1.3.2 It shall conduct regular anticorrosion coating leak detection. A record of
repair for anticorrosion coating leak detection shall be made.
9.1.3.3 It shall, according to the inspection results of external anticorrosion
coating of pipeline, combined with the cathodic protection situations, repair the
defect points of anticorrosion coating of the pipeline. The defect points of
anticorrosion coating located in the area of insufficient cathodic protection and
other areas prone to corrosion shall be repaired in time. The repair of external
anticorrosion coating shall be carried out in accordance with the relevant
provisions of SY/T 5918.
9.1.3.4 Excavation inspections shall be carried out on a regular basis on the
9.2.1 General provisions
9.2.1.1 The external anticorrosion inspection of subsea pipeline shall include
the inspection of pipeline external anticorrosion coating and of pipeline galvanic
anode.
9.2.1.2 Based on the inspection assessment results, the next inspection plan
shall be developed.
9.2.2 Operation and maintenance management of subsea pipeline
anticorrosion coating
9.2.2.1 Anticorrosion coating of risers in splash zone and atmospheric zone.
Appearance inspection of the anticorrosion coating, such as discoloration, swell,
or cracking of the coating, shall be carried out, to determine whether preventive
maintenance is to be taken.
9.2.2.2 Anticorrosion coating of pipelines and risers in underwater areas. For
pipelines exposed on the seabed, visual inspection of the external anticorrosion
coating and underwater thickness measurement may be carried out. By
photography, video, and other methods, the inspection record of pipeline
external anticorrosion coating is carried out. For subsea pipelines, the potential
gradient along the pipeline can be inspected, to judge the missing point of
pipeline anticorrosion coating. When measuring, it shall make sure that the
distance of the measuring electrode deviating pipeline axis is not more than 1
m.
9.2.3 Operation and maintenance management of subsea pipeline
galvanic anode
9.2.3.1 The inspection content of galvanic anode of subsea pipeline mainly
includes but is not limited to.
a) Protection potential of subsea pipelines/seawater;
b) Insulation effect. When the subsea pipeline is protected in sections, the
insulating property of insulation flange (joint) is inspected; and the integrity
and corrosion situations of anticorrosion coating of insulation flange (joint)
pipeline are inspected;
c) The situations of galvanic anode, including. the consumption of galvanic
anode; whether the galvanic anode moves, falls off, damages; whether
the galvanic anode and the subsea pipeline are firmly connected; whether
the galvanic anode surface is covered by marine organism or is
passivated, etc..
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.
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