The Deckhand newsletter · Issue 2 · Energy Street

Sacrificial anodes needed for six offshore structures on each edition of DNV-RP-B401 and DNV-RP-F103

Prepared: Corrosion Deckhand (AI assistant) · Checked: Editor Deckhand · Approved: Vamsee Achanta · 3 November 2026

Sacrificial-anode cathodic protection (CP) protects offshore steel from corrosion with anodes that corrode in its place. DNV sets out CP design in two recommended practices: DNV-RP-B401 for offshore structures and DNV-RP-F103 for subsea pipelines. A subsea export pipeline sized with 9 bracelet anodes (half-shell anodes clamped around the pipe) on the 2010 edition of DNV-RP-F103 needs 34 on the 2019 edition, 277.8 % more, with every other input held fixed.

Each structure is run in the cathodic protection module of the open-source digitalmodel library (MIT licence). In that library, the 2019 edition raises the mean coating breakdown factor for fusion-bonded epoxy, a factory-applied pipe coating, over a 30-year life from 0.0145 to 0.045 (2010 edition, Table A.1; 2019 edition, Table A-1). The coating breakdown factor is the share of the bare-steel current that the coated pipe still needs. For a line carrying fluid at 60 °C, the 2019 edition also raises the mean current density, the current that each square metre of bare steel needs, from 0.060 to 0.075 A/m² (2010 edition, Table 5-1; 2019 edition, Table 6-2). The mean current demand of the 1.5 km section goes from 1.33 A to 5.15 A. Anode mass governs on both editions: the alloy mass needed for the design life sets the count (218.1 kg against 846.1 kg). The count rises 277.8 % and the mass 287.9 %, because each count is rounded up to whole 25 kg bracelets (8.72 to 9, and 33.84 to 34).

Sweep: Design lifeFluid temperature

On the 2019 edition, nine bracelets cover a 10-year design life; on 2010 the same nine cover 30 years. The 2019 count also steps up above 25 °C and above 50 °C fluid temperature, where its current density bands change; the 2010 count steps once, above 50 °C.

The coating breakdown factor does most of the work: changed alone, it raises the anode mass for a 30-year life by 210.3 %, against 25.0 % for the current density alone (the build-up, Figure 2 below).

The other five structures change little (Figure 3 below). Four need the same anode count on all four DNV-RP-B401 editions from 2005 to 2021. The hybrid riser needs one fewer on 2021 (25 against 26, −3.8 %), because the library's 2021 route (its set of values for that edition) sets the closed-circuit potential of aluminium anodes in sediment, the potential of the anode while it delivers current, at −1.00 V against −0.95 V (measured against a silver/silver chloride reference electrode in seawater, Ag/AgCl/seawater). The riser is the only one of the six structures with anodes in seabed sediment, on its suction-pile foundation, so it is the only one that this value changes.

Try it out: find the edition your pipeline's CP design used. If it is DNV-RP-F103 2010, re-check it on the 2019 edition with the same inputs before the next CP potential survey.

The public data set for this study is the platform structures register of the US Bureau of Safety and Environmental Enforcement (BSEE) for the US Gulf of Mexico (US federal government data, retrieved 29 October 2026). Of the 1,301 platform structures still standing in US federal waters of the Gulf of Mexico, 1,124 were installed before 2005, the year of the oldest DNV-RP-B401 edition the library runs; their median installation year is 1983. The register and its map are in Figure 4 below.

Full study

Each structure is one input file in the library. The 84.1 m jacket takes its areas, current densities and anode size from Xu (2023); its other inputs are based on previous project experience. The 60 m wind jacket takes its geometry from Mroczek and others (2023). Every structure is run on every edition route its code accepts, with the anode type, size and alloy, the design life and every other input held fixed. The count is the largest of three checks: anode mass for the design life, current output of new anodes, and current output at end of life.

Table 1 - Anodes required by structure and edition route, runs of 29 October 2026. Four more structures were run and are not shown. A synthetic jacket needs 173 anodes on all four editions. A phased riser base needs the same count on all four, although the final check of its anodes in mud fails on the 2005 to 2017 routes and passes on 2021. A temporary frame gives the same values on all four. A mixed-zone structure runs only on the 2021 route, because the older routes have no anode values at 60 °C.

Export pipeline inputs

The export pipeline's inputs are those of its case file in the library (Table 2). The anode design values, such as the electrochemical capacity, come from the tables of the edition run.

Table 2 - Export pipeline inputs, from the library's pipeline case file (References).

What drives the pipeline change

The coating breakdown factor does most of the work. Changed alone, it raises the anode mass for a 30-year life by 210.3 %, from 9 to 28 bracelets. The current density alone adds 25.0 %, from 9 to 11 bracelets. The two multiply, so together they raise the mass by 287.9 %, to 34 bracelets.

Design life: 10 yr15 yr20 yr25 yr30 yr35 yr40 yr

Tables 3 to 5 - the pipeline sweep behind Figure 1 (above) and the build-up behind Figure 2

Design life (yr)	Bracelets, 2010 (-)	Bracelets, 2019 (-)	Anode mass, 2010 (kg)	Anode mass, 2019 (kg)
10	3	9	57.7	219.4
15	4	15	92.1	352.5
20	6	21	130.4	501.4
25	7	27	172.4	665.9
30	9	34	218.1	846.1
35	11	42	267.6	1,042.0
40	13	51	320.9	1,253.5

Table 3 - Pipeline sweep over design life, fluid at 60 °C, 25 kg net aluminium bracelets.

Fluid temperature (°C)	Bracelets, 2010 (-)	Bracelets, 2019 (-)	Mean current density, 2010 (A/m²)	Mean current density, 2019 (A/m²)
5	8	23	0.050	0.050
20	8	23	0.050	0.050
30	8	28	0.050	0.060
40	8	28	0.050	0.060
50	8	28	0.050	0.060
60	9	34	0.060	0.075
70	9	34	0.060	0.075
80	9	34	0.060	0.075

Table 4 - Pipeline sweep over fluid temperature, 30-year design life.

Design life (yr)	Mean coating breakdown factor, 2010 / 2019 (-)	Bracelets, 2010 (-)	Bracelets, 2019 breakdown factor only (-)	Bracelets, 2019 current density only (-)	Bracelets, 2019 (-)
10	0.0115 / 0.035	3	8 (+204.3 %)	3 (+25.0 %)	9 (+280.4 %)
15	0.01225 / 0.0375	4	12 (+206.1 %)	5 (+25.0 %)	15 (+282.7 %)
20	0.013 / 0.04	6	17 (+207.7 %)	7 (+25.0 %)	21 (+284.6 %)
25	0.01375 / 0.0425	7	22 (+209.1 %)	9 (+25.0 %)	27 (+286.4 %)
30	0.0145 / 0.045	9	28 (+210.3 %)	11 (+25.0 %)	34 (+287.9 %)
35	0.01525 / 0.0475	11	34 (+211.5 %)	14 (+25.0 %)	42 (+289.3 %)
40	0.016 / 0.05	13	41 (+212.5 %)	17 (+25.0 %)	51 (+290.6 %)

Table 5 - Build-up behind Figure 2, fluid at 60 °C, mean current density 0.060 A/m² on 2010 and 0.075 A/m² on 2019. Percentages are the change in anode mass against the 2010 run.

Public data set: BSEE platform structures, US Gulf of Mexico

Source: BSEE Data Center, raw data downloads (Platform Structures). The register lists 7,091 platform structures in US federal waters of the Gulf of Mexico, with type, water depth, location and installation and removal dates; 1,301 have no removal date recorded and are counted as still standing. Of those 1,301, 980 are fixed jackets. By installation year, 849 of the 1,301 were installed before 1993 and 1,124 before 2005 (the 849 are among the 1,124). The register gives installation years, not the CP code edition each structure was designed to. In US practice, the US Code of Federal Regulations lists NACE RP0176-2003, Corrosion Control of Steel Fixed Offshore Structures Associated with Petroleum Production, among the standards that platform plans must conform to, as appropriate (30 CFR 250.901(a)(21)). Its current form is NACE SP0176, kept by AMPP (Association for Materials Protection and Performance); edition to be confirmed.

View: MapInstallation year

Our open-source digitalmodel library runs DNV-RP-B401 editions available. Of the platform structures still standing in US federal waters of the Gulf of Mexico, 1,124 were installed before 2005. This study leaves open how far, if at all, their anode design falls short of the current DNV-RP-B401 edition.

Reusable prompts

Run the six structures of Table 1 on every DNV-RP-B401 and DNV-RP-F103 edition with every other input held fixed, sweep the export pipeline over design life and fluid temperature, compare your counts with Tables 1, 3 and 4, and redraw Figure 4 from the BSEE platform structures register.

Data:

• The six structure input files of the digitalmodel library (MIT licence), in tests/fixtures/cathodic_protection/workflow_inputs: pipeline, multi_component_riser, published_jacket_84m, reference_jacket_60m_members, monopile and manifold.
• BSEE Platform Structures raw data (Bureau of Safety and Environmental Enforcement, US Department of the Interior), PlatStrucRawData.zip on the BSEE raw data page, US federal government data, listed as updated daily. Counted copy retrieved 29 October 2026 10:17Z, SHA-256 bde13c85717ec4ad164f6b95fe0c18758f163dd33efb4d66d949c032b9bc5b52. Recounted from the file of 2 November 2026 (retrieved 3 November 2026 02:28Z, SHA-256 fa24a50febfe689db8446ffa17dd4c29474fbd700fb44ef4ff80c6f78f759b19) with the same counts: 7,091 structures, 1,301 still standing, 980 fixed jackets, 849 installed before 1993, 1,124 before 2005, median installation year 1983.

Code: the cathodic protection module on GitHub (digitalmodel, src/digitalmodel/cathodic_protection, MIT licence); the commit of the study runs is given in References.

Readers are welcome to share their own counts at support@aceengineer.com.

References

Codes: DNV-RP-B401 (2005 with 2008 amendments, October 2010, June 2017 as DNVGL-RP-B401, May 2021); DNV-RP-F103 (October 2010; September 2019 as DNVGL-RP-F103, amended May 2021); NACE RP0176-2003, Corrosion Control of Steel Fixed Offshore Structures Associated with Petroleum Production (current form NACE SP0176, AMPP, edition to be confirmed). Regulations: US Code of Federal Regulations, 30 CFR 250.901, "What industry standards must your platform meet?", eCFR, current to 30 October 2026, ecfr.gov. Software: digitalmodel, cathodic protection module, commit 09089a1, https://github.com/vamseeachanta/digitalmodel; pipeline case file at that commit, pipeline.yml. Other references: D. Xu (2023), Engineering Advances 3(3), 241-245, DOI 10.26855/ea.2023.06.017; M. M. Mroczek, S. R. Arwade and M. A. Lackner (2023), Wind Energy Science 8, 807-817, DOI 10.5194/wes-8-807-2023.