DP Fuel Pt.3 – Fuel Faults & Protections

Introduction: Last week’s article looked at the importance of fuel configurations that support DP redundancy. It pointed at some earlier articles and explained the real purpose of good configurations was to reduce the load on the crew and avoid major problems. It all comes down to operations and the most important part of fuel operations is proper fuel handling by the crew. The configuration supports this, but in the end redundant fuel is created manually by the crew doing everything right. Perfect configurations are easier to operate, and required by rules and clear consciences, but it is the crew who makes it work. This time we look at the threats to that and the steps that should be taken by crew to avoid it.

Detour: The Dali’s blackout and demolition of a bridge raised marine consciousness about already known problems with fuel. A preliminary report has been released and the problem seems to be another unpopular reality – the general lack of marine electrical maintenance leading to unexpected unreliability. I’ve written about that before and will cover the Dali in the May incidents article.

Basics: As shown in the last article, redundant DP fuel systems start with untrustworthy common fuel and, via a series of steps of testing and purification, ends up with officially trustworthy split fuel in the service systems. The final step is the “trust but verify” type of trustworthiness, because split fuel is only real if the crew puts in the work to make it real. Every step taken to create this is also something that can go wrong, so operators need to be aware of the threats, take action to detect them, and take action to protect the fuel system. We will step through the fuel system using last week’s table above. We try to create split fuel systems, because we know the processes and people aren’t perfect, faults sometimes slip through, and we only want to lose one redundancy group. Split systems are important, because real world operation isn’t perfect, and we want to limit faults rather than lose the whole thing. DP2 & 3 systems are made to be fault resistant, but fuel systems need people to drive them there. Finally, as a recent incident showed, when you find problems in one part of the fuel system, it’s time to be suspicious of the rest. You can blame the shipyard for a bad design, and the supplier for bad oil, but no one wants to operate badly. We have professional pride.

Bunker Threats: The series on fuel began a couple weeks ago with an article on two DP threats. One was bad fuel and it was based on an industry report about vessels losing power. This got people’s attention and they wanted more. People started telling private stories about water, particles, different types of oil and chemicals mixed in, biological contamination, and in one case almost 30% wax. There are a lot of people who have been burnt, and some lucky ones who don’t understand what the fuss is about (why we have incident reports to learn from). Problems with bunkering begin before the ship, sometime with dishonest mixing, and sometimes with rust, water, chemical, and biological contamination in the storage or transfer tank, pipeline, and hoses. Onboard, the bunker fill systems often have a little condensation and rust and need kept well sealed to avoid becoming a source of water.

Bunker Solutions: Are you in the habit of buying a car sight unseen, and without taking it for a ride? No? Then why would you accept fuel based on a piece of paper or a jar of fuel that make come from another load. Sure, get the piece of paper and the jar, but pull real samples yourself and run some basic tests then and there. Don’t end up in trouble out at sea. Catch them in the act. Sure, most of the providers are honest, but some also make honest mistakes. Sample at the hose before you take any fuel. Sample onboard at the beginning, middle, and end of fueling. Just because the first gulp is good, doesn’t mean the rest is. Older engineers would do crackle tests and use cheap microscopes, but modern ships should have better tools and use pastes and test kits to catch problems. Do you know how much your sample of fuel should weigh? Some ships lack good sample ports and need to be creative to get good samples, and retrofit something better when they can. If nothing else, you need to run some fuel through a properly working purifier to see if it is churning out mysterious jelly, water, or funny smelling substances. This should be common sense, but crew get busy and owners can sometimes be too cheap for their own good. According to the insurers, lot of engines get damaged by bad fuel. Put in the effort to make sure it isn’t you. Take the paper, take the sample, but verify while safe, rather than finding out at sea.

Storage Threats: Of course, getting good fuel in is just the start. Storage tanks have vents that breathe and allow condensation cycles. Vents and sounding tubes can leak. The boundaries of the tanks are adjacent to other fluids and some bad designs even run pressurized pipes through the tanks. Some tanks don’t have sample ports and some people use inappropriate doping and biocide.

Storage Solutions: Find a way to take samples. You can’t control what you can’t measure. Sounding tubes can be your friend and allow samples, inspection, and doping, but real sample ports and water ports are better. Take samples regularly and sample at the beginning, middle, and end of transfers to the settling tank. Expect contamination to happen and go looking for it. Regularly muck out fuel tanks. There can be hidden build up. Use appropriate biocides and beware of creating periodic die-offs that fill the tank with sludge. Prevent growth rather than regularly kill it. Be sure that additives used do not react with the tank coatings. Most ships use manual valves and the status of these valves needs checked before and after fuel transfers. Automatic valves need occasionally checked for mismatches between the local state and the remote indication.

Transfer Threats: Transfer systems are normally common and normally have two different pumps or purifiers fed from different power redundancy groups. Threats include existing contaminated oil in the pipes, rust, sometimes water contamination if run through tanks (shouldn’t be done), and particles from pump, filter, and valve wear and tear. Probably the biggest threat is mixing clean and contaminated oil via valves that are thought to be closed or by trying to switch sources with a common pipe. Eventually dirty oil has to flush out, but it has to be flushed somewhere and that is usually where you want the clean oil to go. It is absolutely vital that transfer and purification piping be separate.

Transfer Solutions: I’m going to repeat myself like a broken record - sample! There are usually sample ports at the pump and the gross filters used in the transfer system need regularly checked. Some old ships had pipe windows for watching the fuel, but that’s no guarantee. Valves need to be easily accessible, protected against accidental operation, well labeled, and their state locally determinable. These are just prerequisites before we start splitting fuel.

Settling Tank Threats: Perhaps the biggest settling tank threat is not having any or not having one for each redundancy group. Settling tanks aren’t storage tanks and they aren’t purifier recirculation tanks. Settling tanks predate purifiers and are the first layer of purification, when all the previous defenses have failed. They will. It's why we have layered defense. We won’t slack off, but we know we will make mistakes, and this is where fuel starts becoming redundant by catching problems here. Long before purifiers existed, people used settling tanks to settle out contaminations. It’s slow but effective, especially as purifiers don’t always purify. First, we settle and drain impurities, and then we purify what is left. Too many people run the purifier in settling tank recirc with the occasional result () like below.

Settling Tank Solutions: Two types of purification gives two chances to get it right, if they are used properly and in series rather than parallel. Let the settling tank get the big stuff. Fill it up, give it time to settle, and then sample. Send the clean fuel to the purifiers next, unless they are known to be bad. Sometimes, auto-fill systems need disabled to allow settling tanks to be properly filled and drained. Like the storage tanks, the valves need regularly checked and tank regularly mucked out. The settling tanks must be separate from engine return fuel and from equipment in other redundancy groups. Don’t end up with tanks like the above.

Purifier Threats: Purifiers are thought to be the solution to all fuel problems by people who have never had purifiers fail to clean fuel or had them contaminate fuel. Mechanical devices occasionally fail. Malfunctioning purifiers can be a source of water and particle contamination. Sampling purifier outputs is important. I don’t see many expensive purifiers that alarm on output contamination anymore. One fellow that I worked with went on board a vessel and discovered they had ordered the wrong parts and were actually running as clarifiers rather than purifiers. The output looked good, but wasn’t being cleaned. Some vessels, like the one in the article picture, have placed all their bets on a single purifier always working. That certainly improves the chances of messing up. Making them part of the fuel oil transfer system, instead of isolated to fuel purification, almost guarantees contamination will get through. Common water or compressed air problems can sometimes cause common faults. Sludge cannot be allowed to backup into the purifiers, if the drains are clogged or valve shut.

Purifier Solutions: There should be one purifier for each redundancy group to provide the second layer of purification. It should be isolated from other redundancy groups, but able to help other groups that lose their purifier. This requires the ability to reconfigure valves and the need to monitor them (crossover valves normally closed and regularly checked). The purifier needs to have a high enough throughput to allow the settling tank time to settle. I don’t understand why I don’t see output quality alarms anymore. It reduces the number of samples that the crew needs to draw and provides a faster alarm. Perhaps we don’t like paying for calibration or don’t want to know if we have a problem. For redundant DP, we need to know if we have a problem, and the old alarms seemed efficient and effective.

Day Tank Threats: The day tanks are where we are supposed to be clear of problems, and each day tank’s fuel independent of all the others. Instead, day tanks are the sum of all the problems in the previous steps, plus dirty oil returned from engines, water returned from engine coolers, and the typical problems of tanks (leaks, condensation, sludge buildup). If there is a problem with the fuel in one day tank, then it’s pretty likely there will be problems in the others, because the cause is usually in faulty fuel handling and verification procedures. Running engines off of the “good” tank is often an illusion. Some amazing optimists have less day tanks than they have redundancy groups, with some ships having a single tank and others cross connecting. Some people feel safer cross connecting redundant systems, because they figure a bad tank will be compensated for by a good tank, rather than affecting all engines. Probably the worst counter examples are the faults that release a lot of built-up sludge (storm) or a large influx of water. Note that the sludge can happen even when the systems are separated.

Day Tank Solutions: Keep the tanks separate. Regularly muck out the tanks. Monitor the final filters after the day tanks for signs of water and particle contamination. Make sure you have filters that can do that. I miss water alarms. I thought they were useful, especially with water-cooled return lines. Many modern designs have CJC filters dedicated to cleaning each day tank. The older designs used the purifier when it wasn’t transferring fuel (again concerns about ensure the purifier actually is purifying rather than making things worse). Overflows should go to overflow tanks, especially with water cooled returns. Many of the storage and setting tank solutions apply here, as tanks have similar problems, but its worse for day tanks, as the engines are a source of pollution as well as the things that they must reliably supply clean fuel to.

Conclusion: The configuration conclusion was to “Keep It Simple, Stupid” and design split systems that ease operator burden. The operations conclusion is “Hustle”. Take Murphy’s Law seriously, figure out what can get you, and how you will stop it. I wish designers spent more time making this easier and that some of the old alarms were still used. Crew are busy, but they can’t afford to become complacent to the threats, and need to maintain good fuel handling practice to avoid fuel caused DP incidents. Experienced people will recognize most of the faults mentioned and remember incidents associated with them. DP crew aren’t people who ride along as the equipment does the work, they are the ones who make sure it happens right in the first place, and fuel is a good example.