Steam Bubble Cavitation

Understanding Corrosion: Cavitation

Cavitation is a fascinating yet destructive phenomenon that can have a profound impact on the integrity of materials, particularly in steam systems. This article delves into the world of cavitation and its role in pitting corrosion, shedding light on how it can lead to significant damage to steam heater tubes and piping systems. 

 

Cavitation occurs when steam bubbles rapidly collapse, generating an extraordinary amount of pressure on the adjacent material. This can result in the formation of pin-sized to larger holes, which can ultimately lead to the leaking of steam heater tubes. The process is driven by the collapse of steam bubbles, creating a highly localized and intense pressure that causes damage to the material's surface. 

Fig 1.- Tube Inside Cavitation | Motic Panthera SMZ171, Moticam 10 Stack

Image Credit: Willem Cramer

Cavitation erosion is closely linked to the behavior of flash steam in the system. Flash steam occupies a relatively large volume but rapidly condenses when it loses heat, which is transferred through the tube wall into the surrounding fluid. This sudden condensation of flash steam results in a significant change in volume. 

The specific volume differences between steam and condensate are key to understanding cavitation's destructive potential. When flash steam condenses, it creates a large void that is swiftly and often violently filled by adjacent condensate. This rapid filling of the void generates shock waves known as water hammer. 

Fig 2.- Tube Outside Cavitation | Motic Panthera SMZ171, Moticam 10 Stack

Image Credit: Willem Cramer

The rapid collapse of the flash volume and the associated shock, caused by high-velocity condensate filling the void, can have severe consequences. The force generated by water hammer and the erosion caused by the swift filling of voids can result in significant damage to piping systems. In conclusion, cavitation is a complex phenomenon with the potential for significant damage in steam systems. The rapid implosion of steam bubbles, driven by specific volume differences between steam and condensate, can lead to the formation of holes and result in pitting corrosion. Understanding the mechanics of cavitation is crucial for preventing and mitigating the destructive consequences it can have on steam heater tubes and piping systems.

© willemsmicroscope.com

Fibrosarcoma cat

A fibrosarcoma is a malignant tumor of mesenchymal connective tissue cells. Fibrosarcoma mainly occurs as a solitary tumor in the older cat. It can occur in several parts of the body. Usually on the trunk and often also between the shoulder blades, because injections are usually given here. First there is an injection site reaction that degenerates neoplastic. The rabies vaccine is known to be a possible cause of this. It is a malignant derailment of the dermal and subdermal connective tissue cells. The sarcoma grows locally very infiltratively and aggressively, not metastasizing quickly. But if so, then to the lungs and lymph nodes. Fibrosarcoma can also occur in young cats. In these cases it is often induced by a virus and there are multiple tumors over the entire body.

Cracks in the pipe

The cracks in the austenitic stainless steel sample on the picture below are most likely a case of Stress Corrosion Cracking (SCC). SCC is the cracking induced from the combined influence of tensile stress and a corrosive environment (such as chlorides). The impact of SCC on a material usually falls between dry cracking and the fatigue threshold of that material. The required tensile stresses may be in the form of directly applied stresses or in the form of residual stresses. The problem itself can be quite complex.

Pear rust and Junipers

Pear Rust is an increasingly common fungal disease in pear trees. This disease can significantly slow the growth of a pear tree, and the tree will also give less fruits. Pear Rust is a fungus that cannot stay the whole year on the pear: in winter the tree has no leaves and the fungus is only present there. In winter, the fungus needs a Juniper to overwinter. After the winter the fungus makes spores, which are spread through the air. The spores fall on the pear tree, causing the fungal disease.

Escherichia coli are usually blamed

Cystitis, or bladder infection, is the most common urinary tract infection. It occurs in the lower urinary tract (the bladder and urethra) and nearly always in women. In most cases, the infection is brief and acute and only the surface of the bladder is infected. Deeper layers of the bladder may be harmed if the infection becomes persistent, or chronic, or if the urinary tract is structurally abnormal. Uncomplicated urinary tract infections (UTI’s) are due to a bacterial infection, most often E. coli. Microscopic examination of the urine sample shows e.g. the presence of white blood cells and bacteria.

Symptoms of lower urinary tract infections usually begin suddenly and may include

Yellow, widespread and strong

Xanthoria parietina is a yellowy orange colored leafy lichen that is one of the most common species around. The yellow chemical xanthorin is thought to be produced as a defense against UV radiation to which it is exposed in its normal habitat like cement tiled roofs, exposed twigs and branches etc.

How to be heat and drought resistant?

The Oleander has big, red, white or yellow, highly fragrant flowers. The 7 - 8 m high shrubs are spread from the Mediterranean to East Asia, growing in sunny locations and near watercourses. In North West Europe it is often drawn as a container plant.

Its leathery, lance-shaped leaves show the characteristics of xeromorphic - that means drought resistant - sun plants. Oleander is adapted to the very hot and dry borders of watercourses in summer.

Holding on to your host

Moniezia expansa is primarily present throughout ungulates of Europe, Asia, Africa, America and Australia. This parasite has also been found in South American countries, including Peru and Argentina.

Like all cestodes, or tapeworms, M. expansa are flat with multiple segments of proglottids, used for producing gametes for reproduction. The adult bodies lack digestive tracts and are covered with microvilli to increase surface area for the absorption of nutrients. Moniezia expansa adults can reach lengths of 4 to 5 meters and are separated into three sections including the scolex, neck and strobila. The scolex is usually less than 1 millimeter, and contains suckers and hooks to assist in holding on to the host. The small neck produces immature proglottids, while the large strobila (main body) consists of a large chain of mature male and female proglottids.

Breathing through your roots?

Mangrove is a type of forest in the tropics and subtropics, located along a low coast or a river, which is submerged at high tide, is sheltered and muddy, has a salty soil and is characterized by a vegetation consisting of trees and shrubs with breathing roots or aerial roots.

Diamonds are forever

The first diamonds were discovered more than five thousand years ago in India and have held mankind for many enigmas since then: how was it that diamond was harder than any known matter, what was the composition of this mineral, etc.