August 9, 2007
Gard warns of quality risks with low sulfur fuels
The Gard P&I Club is warning that fuel oil quality may be at risk as refiners explore more advanced production/blending processes to satisfy the global demand for low sulfur fuel.
Gard notes that fuel oil quality is directly related to safe ship operation. And it cites one example where fuel quality problems appear to have resulted in a vessel requiring $1.2 million of engine repairs and 41 days off-hire.
In a Loss Prevention Circular issued this month, Gard warns that the traditional method of assessing fuel oil quality and suitability may be unreliable in certain circumstances. It says that, in relation to the delivery of low sulfur fuel, a growing number of deliveries with excessive Aluminum and Silicon content, problems with fuel stability and ignition quality have been reported.
Fuel oil ignition and combustion quality is not yet part of the ISO 8217 specification. The Calculated Carbon Aromatic Index (CCAI) has historically been the default method of estimating heavy fuel oil ignition quality. Fuel oil density and viscosity are the key parameters needed for calculating the CCAI, and the number 860 has for years been considered the limit for an acceptable ignition quality for a trunk piston engine.
With refineries increasingly using Heavy Cycle oil (HC) in the blending process to achieve low sulfur values, the CCAI and the Calculated Ignition Index (CII) have often been found to be too inaccurate and inadequate to detect fuel with poor ignition properties. The most widely used equipment for fuel ignition tests has been the FIA- 100 FCA, which is already available from some test laboratories and comes with an Institute of Petroleum approved test method, IP 541/06.
Typical engine problems experienced when using a fuel oil with poor ignition properties are:
Illustrating the consequences of poor ignition and combustion properties, Gard cites a recent case where a vessel reported a main engine knocking sound and numerous piston seizures. Temporary repairs were executed, but the chief engineer did not realize that the problems might have something to do with the fuel oil properties, and opted to continue running the engine at reduced RPM with the same fuel oil until the vessel reached a port of refuge.
With the engine opened up severe damages were discovered to all cylinder units. Main bearings had to be renewed and the crankshaft's main bearing journals had to be polished. in addition numerous other parts had to be inspected/overhauled. The damage repairs amounted to USD 1.2 million, and involved 40 days off-hire.
During repairs it was felt that the damage seen had similarities to that which could have been caused by fuel oil with poor ignition and combustion properties, and a decision was made to perform an ignition quality test.
The diagram illustrates the results from the fuel oil ignition tests performed with the FIA 100/3 (A), compared with a reference curve illustrating test results for 'normal' fuel oil.
A: Reference curve. Normal peak pressure and an ignition delay of 5.9 ms (millisecond). Start of main combustion, 7.85 ms.
B: Our vessel. Low peak pressure with "after burning" effects. Ignition delay 13.8 ms, start of main combustion, 21.6 ms.
Among the comments made by the laboratory were;
Gard says lessons learned are: