Pre-Commissioning Chemical Cleaning and Passivation of Ship Piping Systems

Abstract: New-build piping is not clean piping. Manufacturing leaves mill scale, cutting fluid and weld spatter; storage and transport leave protective grease and flash rust; installation adds thread sealant, gasket debris and grinding dust. Left in place, these contaminants blind filters, seize valves, wear fuel-injection and hydraulic components and start under-deposit corrosion — and the rework lands exactly when sea trials are due. This article sets out the four-step pre-commissioning process — degreasing, acid cleaning, rinsing and passivation — for sea water, fuel, lube oil, hydraulic and ballast piping, explains how chemical systems differ for carbon steel, stainless steel and cupronickel, and lists the cleanliness and passivation-film tests and the documentation an owner and class society will ask for.

1. Why New-Build Piping Must Be Cleaned Before Commissioning

New pipes are not clean pipes. Three stages put contamination inside the line: manufacturing leaves mill scale, cutting fluid, burrs and weld spatter; storage and transport leave protective grease on the bore and flash rust where rainwater has entered; installation adds thread sealant, PTFE tape debris, gasket offcuts and grinding dust. The film sits tight against the pipe wall, and if degreasing is incomplete the oil blocks the acid from the rust underneath, so the acid stage achieves very little.

The damage is functional. Rust and oil films in sea water cooling lines cause under-deposit corrosion, and pitting in cupronickel is hard to repair. Particles in fuel and lube oil lines reach injectors, bearings and close-tolerance components and cause wear and sticking. Hydraulic lines are the most particle-sensitive of all: oversize metal and sealant debris leads directly to valve failure, and rework after commissioning usually means stripping the whole run out again. Debris in ballast and bilge lines blocks strainers, nozzles and valves.

Piping is ready for cleaning once block outfitting and quay outfitting are underway, and pre-commissioning cleaning is normally scheduled around system integrity testing. Owners and class societies set explicit cleanliness requirements for piping before mooring and sea trials, and piping flushing plus cleanliness inspection is a required stage — so cleaning is both a quality requirement and a milestone item.

2. Pipe Systems and the Contaminants They Carry

Ship piping covers a wide range of materials — carbon steel, stainless steel, cupronickel and titanium — and one chemical system cannot serve all of them. Pipe material and bore condition are confirmed first, then the work is planned system by system. Deposit type can be identified using the simple qualitative methods in Table 1 of GB/T 25146-2010; in new-build lines the deposits are mainly rust and oil, quite different from the mixed deposits found in operating equipment.

Systems containing stainless steel or cupronickel need particular care: both are sensitive to chloride, and chloride in the cleaning solution is the main driver of pitting and stress-corrosion cracking. Clause 5.2.9 of GB/T 25146-2010 requires the chloride content of the cleaning solution to be no more than 25 mg/L when stainless steel is present. For ship piping this should be treated as a hard constraint on chemical selection and water quality control, not something to test for at acceptance.

3. The Four-Step Process: Degrease – Acid Clean – Rinse – Passivate

The main difference from cleaning a single equipment item is loop organisation. By system, the pipe runs to be cleaned, a mixing tank and an acid-resistant pump are connected into a circulation loop with temporary hosing; instruments, strainers and valve internals are removed or isolated; loops are kept short and unobstructed. Circulation velocity is generally 0.5–1.5 m/s — too low gives poor scouring, too high raises system resistance and air entrainment.

Step one, degreasing. Carbon steel systems are circulated with LX-902 compound cleaner (alkaline saponifying type) together with Surfactant and Na₂CO₃-based assistants to strip protective grease, cutting fluid and construction oil from the bore. Whether the oil is gone is not judged by eye: any one of the four methods in clause 5.3.3.1 of GB/T 25146-2010 may be used — no oil trace on filter paper, no fluorescence under UV, the camphor-ball rotation test, or carbon tetrachloride oil content no greater than 125 mg/m².

Step two, acid cleaning. Carbon steel systems are cleaned mainly with LX-903 compound cleaner (Sulfamic Acid based) plus a dedicated inhibitor; stainless steel systems use a Citric Acid based cleaner with no chlorides; cupronickel runs form their own loops and use a citric-acid system with a BTA-type copper inhibitor, with temperature and time set by coupon tests. Hydrochloric-acid products remove rust quickly but leave residual chloride and pitting risk, and should be avoided in ship piping containing stainless steel or cupronickel. Acid strength and iron content are titrated during cleaning; when Fe³⁺ exceeds 1000 mg/L a reducing or complexing agent is added, or the solution is replaced (clause 5.2.10). Actual concentrations and ratios are set from deposit type, thickness and coupon results, and are not listed here.

Step three, rinsing, and step four, passivation. Immediately after acid cleaning the system is rinsed with demineralised or softened water until pH and iron levels are on target, preventing flash re-rusting and over-pickling (clause 5.2.8). Passivation follows: carbon steel systems form a film with a passivating pre-film agent, stainless steel systems use a citric-acid passivation system. Coupons of the same material as the pipe are fitted throughout as required by clause 5.2.11, and the corrosion rate is controlled to Table 2 of the standard — carbon steel no more than 2 g/(m²·h) in laboratory verification and 5 g/(m²·h) in field measurement; stainless steel and copper alloys no more than 1 g/(m²·h) and 1.5 g/(m²·h) respectively.

4. Cleanliness Testing and Handover Documentation

Acceptance for ship piping is not a visual judgement; it is a set of recordable, repeatable test results. Oil residue, passivation film, corrosion rate and residual chloride all have standard methods, while particle cleanliness follows the owner's and the equipment maker's requirements.

Handover documentation normally comprises: the cleaning method statement and process cards, chemical certificates, same-material coupon corrosion records, process records (temperature, time, acid strength and iron titration data), rinsing and flush water reports, cleanliness and passivation-film test reports, and waste collection and disposal records. Complete, traceable documentation is what owners and class societies look at hardest, and Blue Star Cleaning compiles it into a project file for handover.

5. Safety, Waste and Site Organization

Ship piping cleaning is usually carried out in engine rooms, pump rooms and double bottoms, so confined-space permits apply: forced ventilation and oxygen/flammable-gas testing before entry, a safety watchman and external rescue equipment, and explosion-proof lighting and power tools. Acid areas are cleared and isolated with warning signage; crews wear acid suits, goggles and respirators, wash water and first-aid supplies are kept close by, and pipe ends are never pointed at people.

Waste is collected throughout: acid and rinse water is neutralised to pH 6–9 and handed to a licensed contractor or discharged to the yard's environmental requirements, never into the bilge system or over the side; oily degreasing waste and passivation waste are collected separately and not mixed with acid waste. The method statement states the waste containers, transfer route and final destination so that the whole path is traceable.

6. Case Study: Pre-Commissioning Cleaning of New-Build Ship Piping

In August 2026 Blue Star Cleaning carried out pre-commissioning cleaning of piping on two new-build vessels at a shipyard in East China, covering sea water cooling, fuel and lube oil, hydraulic and ballast systems in carbon steel, stainless steel and cupronickel. Sampling before cleaning found protective grease film still on some bores, mill scale and weld spatter around welds, and flash rust in runs that had been stored longer — a classic rust-and-oil mix.

Work was organised into circulation loops by system, with cupronickel runs prepared separately, and the four steps carried out in sequence. Chloride content was monitored throughout on loops containing stainless steel and held below 25 mg/L. Acid strength and iron content were recorded every 30–60 minutes, with same-material coupons fitted. After cleaning each loop was flushed and inspected: oil residue passed the filter-paper and UV methods, carbon steel passed the red-spot test and stainless steel the blue-spot test, coupon corrosion rates stayed inside the standard limits, particle cleanliness was inspected to the owner's requirements, and all loops passed at the first attempt. Neither vessel suffered pipe-stripping rework for cleanliness before sea trials.

7. Frequently Asked Questions

Q1: The pipes are new — why do they need chemical cleaning?

New does not mean clean. Manufacturing leaves mill scale and weld spatter, storage and transport add protective grease and flash rust, and installation brings in sealant debris and grinding dust. Blue Star Cleaning degreases first and then acid-cleans by system, so that an oil film cannot block the acid.

Q2: Will acid cleaning and passivation pit or thin stainless steel piping?

No. Pipe material is confirmed and coupon tests are run first; where stainless steel is present the chloride content of the cleaning solution is held to no more than 25 mg/L under GB/T 25146-2010, the corrosion rate is controlled to no more than 1 g/(m²·h) per Table 2, and same-material coupons are fitted throughout. No pipe wall has been damaged by cleaning in Blue Star Cleaning's 25+ years of work.

Q3: Must the cleaning be done in dry dock, and can it delay delivery?

Piping cleaning normally follows block or quay outfitting alongside system integrity testing, is grouped by system, and runs several loops in parallel so that it can be interleaved with other yard trades. Blue Star Cleaning mobilises ahead of the yard programme and works back from the loop schedule; call 18952832843 to plan the window.

Q4: How is cleanliness proved, and what documents do owners and class societies accept?

By standard methods on record: oil residue by any one of the four methods in clause 5.3.3.1, the red-spot test for carbon steel and the blue-spot test for stainless steel passivation film, together with coupon corrosion rates and process records. Blue Star Cleaning issues the test reports and the full process file for handover to the yard and owner.

Q5: How is ship piping cleaning priced?

Pricing follows the pipe system, diameter and length, material, deposit type and number of loops; stainless steel and cupronickel systems are quoted separately because their chemical systems differ. Blue Star Cleaning surveys on site and analyses deposit samples free of charge before issuing a plan and quotation, with invoicing after acceptance. Tel: 18952832843.

All cleaning processes and acceptance criteria in this article follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment.

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