Jacketed (double-wall) fuel injection pipes on marine diesel engines: what SOLAS requires

SOLAS requires the external high-pressure fuel pipes on a ship’s diesel engines, the ones between the injection pumps and the injectors, to be jacketed: if a pipe cracks, the fuel has to stay inside an outer pipe and be collected, and an alarm has to be given. The requirement came in with the 1994 amendments and, for ships built on or after 1 July 2002, sits in regulation II-2/4, paragraph 2.2.5.2.

What exactly does the SOLAS regulation say?

It asks for three things: a jacketed pipe, collection of leakage, and an alarm. In the SOLAS text published by the UK Maritime and Coastguard Agency (MCA), the paragraph opens:

“External high-pressure fuel delivery lines between the high-pressure fuel pumps and fuel injectors shall be protected with a jacketed piping system capable of containing fuel from a high-pressure line failure.”

SOLAS II-2/4.2.2.5.2, as published by the MCA on GOV.UK, 15 September 2015

The paragraph then defines the part: the high-pressure fuel pipe is placed inside an outer pipe, “forming a permanent assembly”. Its last sentence reads: “The jacketed piping system shall include a means for collection of leakages and arrangements shall be provided with an alarm in case of a fuel line failure.”

The paragraph does not specify the jacket material, where the leakage is collected, or the type of alarm. The MCA publication reflects the 1 July 2002 edition of SOLAS; the 1994 text that older ships fall under, II-2/15.2.9, sets the same three conditions.

Which ships and which engines does it apply to?

The ship’s date of construction decides which paragraph applies. Chapter II-2 as renewed by the 2000 amendments applies to ships constructed on or after 1 July 2002; older ships stay under the previous chapter. Türk Loydu’s circular S-P 16/13 reproduces that text: II-2/15.2.9 requires the jacketed pipes, and 15.2.12 gives existing ships a deadline and one exception.

Ships constructed before 1 July 1998 had to comply by 1 July 2003. The exception is theirs alone, and narrow: on engines of 375 kW or less with fuel injection pumps serving more than one injector, “a suitable enclosure” may be used instead of jacketed pipes. The United Kingdom keeps this wording for its older ships in its 2023 notice MSN 1900.

For the oldest ships the sources do not agree. Türk Loydu’s circular S-P 28/13 (2013), based on the 2001 edition of SOLAS, says the requirements “apply to all SOLAS convention ships from 1 July 2003”. The MCA’s instructions to its surveyors say a later IMO resolution limited them to ships constructed on or after 1 February 1992, and only recommend sheathed pipes on anything older. Your flag State and class society decide which reading applies.

On engines, IMO’s 2009 guidelines apply the requirement to internal combustion engines “installed in any area on board ships irrespective of service and location”, and leave out lifeboat engines and diesel fire pumps.

Why does the rule exist?

Because a crack in a high-pressure pipe turns fuel into a fine spray, and a hot surface can ignite it. IMO’s 1994 guidelines recognise that “oil fuel, lubricating oil and other flammable oil system failures are a major source of shipboard fires”. The 2009 guidelines explain the mechanism: the smaller the droplets, the greater the fire risk, and fuel forced through a small opening at high pressure is atomised.

“Therefore, a small crack in a high-pressure oil fuel pipe may lead to a most dangerous situation.”

IMO, MSC.1/Circ.1321, 11 June 2009, part 2, chapter 2, paragraph 1.2

Neighbouring provisions cover the rest. Regulation 4.2.2.6.1 requires surfaces above 220°C that leaking fuel could reach to be insulated. Regulation 4.2.2.5.3 keeps fuel lines away from hot units and has them screened; the interpretation the MCA reproduces asks for spray shields on the flanged and threaded joints of fuel lines above 0.18 N/mm² near such units. Road vehicles are covered in our article on diesel leaks.

What does a jacketed pipe consist of?

A jacketed, or double-wall, pipe is one assembly: the high-pressure pipe, an outer pipe around it, and the space between them, which leads leaked fuel to a drain with an alarm. IMO’s 2009 guidelines also call it a sheathed pipe and name two designs in use, rigid and flexible. In both, the sheathing has to enclose the pipe fully and “resist penetration by a fine spray or jet of oil from a failure in the pipe during service”.

The guidelines set three more conditions. The annular space and the drainage must be sufficient that pressure cannot build up and rupture the sheath, even if the inner pipe fractures completely. The drainage must keep fuel out of the lubricating oil and “include an alarm to indicate leakage has occurred”. And the suitability of such pipes “should be demonstrated by prototype testing”.

For the enclosure allowed on small engines, the interpretation in Türk Loydu’s circular (SC189) sets a limit: “Screening by the use of reinforced tapes is not acceptable as a suitable enclosure.”

What should be checked at maintenance and when a pipe is replaced?

IMO’s 2009 guidelines say “little additional maintenance or periodic inspection is required” to keep jacketed fuel lines in working order. Their one explicit instruction is about refitting:

“However, jacketed pipes should be inspected regularly and any drainage arrangement which may have been disconnected for maintenance purposes should be refitted on completion of the task.”

IMO, MSC.1/Circ.1321, part 3, chapter 1, paragraph 3.4

1. Reconnect the leak-off line. This is the step the guidelines name.
2. Refit every clamp and support. The guidelines list inadequate support, frequent partial dismantling and reassembly, and vibration among the main causes of fuel system failures.
3. Examine the threaded connections every time. The guidelines ask for this at each dismantling. The 1994 guidelines add a caution: “Care should be taken not to overtighten fittings during these checks.”
4. Test the leakage alarm. Neither set of guidelines says how or how often. The engine maker’s manual and the ship’s planned maintenance system do.
5. Do not fit a single-wall pipe in its place. The regulation does not say so outright; it follows from its definition. A plain pipe has neither the outer pipe nor the leak collection it requires.

What do you give the supplier when ordering a replacement pipe?

The engine’s identity, the pipe’s position, and the old pipe or a drawing. No source gives such a list; the one below is our suggestion.

• Engine make, type and serial number.
• Which cylinder the pipe serves, and the engine maker’s part number if known.
• The old pipe or a dimensioned drawing, with its sheath and leak-off connection.
• Whether the sheath is rigid or flexible, and where the leak-off connects.
• The document your class society expects with a replacement pipe; ask before you order.

Two articles cover measuring and samples: how to describe a line with no readable part number and how to have a discontinued line made from a sample.