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Practical Ideas for the Engineer Weak Points of Present Day Condensers Described oe | by Naval Officer--Producer Gas as Marine Fuel HE importance of the elimina- i tion of condenser defects has ; been recognized in the mavy for many years, and as this question is assuming an increasing degree of prominence in the mercantile marine and land installations, it is hoped that some remarks on service experience may be of interest and value. In the early days of low powers and comparatively high ratio of ma- chinery weight in war vessels, a high standard of purity of feed water was not absolutely essential, and owing to its protective qualities a certain amount of boiler scale was not par- ticularly objectionable. Under these circumstances the boilers were fre- quently worked with a slight density, and the admission of small amounts _ of salt water to the feed was a mat- ter of no great moment, and {ndeed would not ordinarily be detected. Further developments in the direc- tion of greater horsepower per unit weight of machinery required the at- tainment of the maximum boiler effi- ciency compatible with the type of boiler then employed, and the pres--- ence of any nonconducting scale upon the heating surfaces could no longer be tolerated. A _ high standard of purity of feed, therefore, became es- sential, and condenser defects, hitherto unnoticed, became more and more apparent. Subsequently the demiands for maximum power on a minimum weight necessitated the development of the water-tube boiler, which in its present form is peculiarly sensitive to the quality of feed supplied, and a condenser defect which formerly would have been regarded as of little importance is now attended by results which are out of all proportion to the magnitude of the defect itself. Results of Defects Among the immediate results follow- ig upon such ia defect as a small 'perforation are: (a) A rise in the density of the boiler water followed by priming (that is, the passage of water with the steam through the system), with consequent possible damage to fast-running reciprocating auxiliaries, and undue wear (erosion) of turbine nozzles in modern vessels; and unless the evaporation is consider- ably eased, and the engines either slowed down or stopped, the mechanical dam- From a. paper read at a meeting of the Institute of Metals, at Barrow-in-Furness, England, Sept. 16, 1920. The author, G. B. Allen, is an engineer lieutenant-commander, royal navy. age caused by the water passed over may be considerable. (b) The deposition of scale upon the heating surfaces. : (c) The commencement of serious corrosive action in the system, includ- ing both boilers and turbines, the first named being particularly severe in the highly forced boilers of the present day. It is on these grounds, both of re- liability and durability, that the im- portance of maintaining a pure "feed" rests. Fortunately, the proportion of de- fective tubes compared. with the num- ber of tubes on service is extremely low and is not greater than 50 in 1,000,000 per annum; but if it be real- ized that in a large vessel fitted with some 48,000 tubes of a total length approximating to 115 miles, such a small defect as 'a vs-inch diameter per hole or one cracked tube may render the vessel unmanageable in a moment of great-stress, it will be evident that it is a matter of great importance to secure immunity from such de- fects and, moreover, one which re- quires considerable investigation and joint co-operation between 'the manu- facturer, the metallurgist, and the user. Care in Fitting Many of the early difficulties €xperi- enced were found to be due to faulty design and 'manufacture, but these, which concerned accuracy of fitting rather than faults in the tubes them- selves, have been gradually eliminated. Defects of this nature may be sum- marized as follows: 1, Insufficient support of tubes be- tween the tube plates. 2. Holes in diaphragm plates too large. 3. Holes in tube plates too large or too small. 4. Unsuitable packing. 5. Slackness of ferrules in plates. 6. Steam or drain orifices unsuit- ably placed, allowing steam and hot water, sometimes contaminated with oils, to impinge on certain tubes. Insufficient support leads to undue vibration of ithe tubes, and although this has been largely rectified by the provision of suitable and unequally spaced diaphragm plates, and by lim- iting the diameters of the tubes and the holes through which they pass, a certain clearance must of necessity be allowed. The effect of vibration, more especialiy in high-speed vessels, can- not be ignored. tube Experience has shown the necessity of adhering to rigidly defined limits 614 in regard to the tolerances of tubes and holes in tube plates, both on the score of guarding against the fit being too close, with consequent abnormal strain thrown on the tubes when screwing up the glands, and also of guarding against too loose a fit, re- sulting in the packing being forced between tube and tube plate and probable leakage. Similarly, the exact concentricity of ferrules and_ tubes within narrow limits is of importance. Since the adoption of limiting clear- ances, defects of this character have to all intents and purposes'. been eliminated. Causes of Corrosion Investigations into the general problem of the naltture of the under- lying causes of corrosion within the alloy itself have resulted in various theories, none of which has as _ yet met with general acceptance, and in the present stage the most we are able to do is to endeavor to trace each defect to its immediate observable source. In many cases this is pos- sible and a fairly simple matter; but in Others, such as may be covered by the description "general corrosion," considerable difficulty may be experi- enced. Fortunately such cases are comparatively few, and though it may be argued that this comparative free- dom hardly justifies the necessary expense and trouble of further inves- tigation, yet from naval considerations it is just these few cases for which remedy must. be found. The information available at the admi- talty is derived from reports forwarded by ships as failures occur. Owing to the conditions of service during hostil- ities it has been impossible to obtain -- complete records of all failures during that period, but from examination of reports received since the cessation of hostilities, the following statement has been deduced to show the present causes of failure in the proportion in which they have occurred: Per Cent of total failures (a) Deterioration at inlet ends 18. (b) Perforation due to local pitting 14.8 (c) Perforation due to obstruction : 14.8 (d) Perforation due to steam impingement 0.4 (e) Crushed ends ., 3 ; ; : - oc (f) Splitting . ' : : : <3. (g) Perforation due to-contaminated circulating water 1.0 (h) General corrosion : 2 The large proportion of failures due to deterioration at the inlet ends of the tubes is noteworthy. Generally speaking, there is a marked thinning