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compressor blade damage

compressor blade damageclick for a larger image
Various types of damages that compressor blades can sustain. Only one or two may take place simultaneously though these have been combined in this illustration.
The various types of damages to compressor blades and their appearances are as follows:
i. Bend. The blade gives the appearance of ragged edges. Smooth repair of the edges or surface in question can be carried out, but the extent of the damage that can be repaired is limited.
ii. Bow. The main source of this type of damage is a foreign object. The blade is bent at the tips and the edges.
iii. Burning. The damage is caused by overheating. The surface of the blade is discolored. If the overheating is severe, there may be some flow of material as well.
iv. Burr. A ragged or turn-out edge is indicative of this type of damage. This takes place during the grinding or cutting operation of the blade at the manufacturing stage.
v. Corrosion. Oxidants and corrosive agents, especially moisture present in the atmosphere, are the main reasons for the corrosion or pitting of the blades. Normally, regular washing is sufficient to prevent it. The blade gives a pitted appearance, and there is some breakdown of the surface of the blade. Also called pitting.
vi. Cracks. Excessive stress from shocks, overloading, or faulty processing of blades during manufacturing can cause cracks and result in their fracture.
vii. Dent. These can be caused by FOD (foreign-object damage) or strikes by dull objects like those in bird strikes. Minor dents can be repaired.
viii. Gall. This type of damage is from the severe rubbing of blades, in which a transfer of metal from one surface to another takes place.
ix. Gouging. The blade gives the appearance of displacing material from its surface, and a tearing effect is prominently visible. This type of damage is from the presence of a comparatively large cutting material or foreign body between moving parts.
x. Growth. The damage manifests itself in the form of elongation of the blades. Growth type of damage takes place because of continued and/or excessive heat and centrifugal force.
xi. Score. Deep scratches are indicative of scoring, which is caused by the presence of chips between surfaces.
xii. Scratch. Narrow and shallow scratches are caused by sand or fine foreign particles as well as by mishandling the blades.
xiii. Pitting. Pitting takes place because of atmospheric corrosion, especially seawater. The surface of the blade shows signs of pitting.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
References in periodicals archive ?
The difference between wholesale petroleum products and crude oil prices, known as the crack spread, is an important determinant of refining margins.
And entering 2011, crack spreads are inspiring flashes of deja vu.
The crack spread, or profit for processing three barrels of oil into two of gasoline and one of heating oil, rose to a four-month high last week as fuel demand climbed.
Lower diesel shipments from China for July offered some support to the Singapore gas oil crack spread to $6.50 a barrel, up from $6 lows earlier in the week.
Figure 1 shows the average month crack spread in the U.S.
"Throughout the quarter refining fundamentals improved, gasoline and distillate inventories rebalanced, and the April blended crack spread of $18.80 is more than double the first-quarter average.
Refining margins, as typified by generic markers such as the 3-2-1 crack spread, have also showed renewed strength after weakening in the first week of May.
In Asia, steady demand from India and Pakistan soaked up gasoil cargoes, which lent support to mid-distillate crack spreads. Petroleum Argus of May 10 said ultra-low sulphur gasoil cargoes from Asia-Pacific could potentially move to North-West Europe (NWE), where the diesel crack spread to Dated had firmed to a 2010 high of $14.45/b.
Current refinery margins--what is called the "crack spread"--the difference in prices between the cost of a barrel of crude oil and money paid for the products made from the barrel--are high, running in the $20/barrel range.
The relative strength of gasoline to crude oil in February pushed the crack spread - the profit margin in buying crude oil and selling gasoline - to nearly $10/b, the highest level since August 2007.
In refining terminology, the difference between what is paid for the crude and what the products sell for is called the "crack spread." According to Muse, Stancil & Co.