Damage that valves suffer and why
Can valves get sick? Who or what causes valve damage?
Next, we present a series of pathologies or damage suffered by the valves, our beloved control tools, due to the slow wear of the process or suffering an acceleration in its deterioration due to some human negligence.
A valve installed without regard to a method of protecting it from weather factors, such as a coating, can stop working long before the end of its useful life.
Environment damage
EXTERNAL DAMAGE THAT VALVES SUFFER
The valves can be attacked from the outside, that is, damages that are not generated by the fluid that passes through them. In any process installation, it must be considered whether the valve is protected or exposed to the elements, whether there is dust, gases, humidity, whether the material of the body is compatible with the substances corrosive substances in the environment, live microorganisms, saline environments or condensation from the insulation itself. A valve installed without taking into account a method that protects it from weather factors, such as a coating, can stop working long before the end of its useful life.
To avoid these attacks we must carefully select the materials in contact with the outside of the valve and protect exposed areas such as pipes, actuators or positioners as well to carry out periodic maintenance.
Damage inside the valve
INTERNAL DAMAGE THAT VALVES SUFFER
The internal damage suffered by the valves is produced by the fluid that passes inside and affects the all the elements that are in contact. In this section we are going to go into detail, since the valves can get sick due to various factors.
Abrasion
The speed and particles in suspension of an internal fluid cause a loss of the material that makes up the valve, which causes some parts to be more polished or worn than others, normally the points where the speed is higher, the sealing medium and the joints or seats.
Abrasion consists of the loss of material due to the impact of suspended particles.
The damage of abrasion will depend on the angle of incidence, the velocity of the fluid, the density and size of the particles in suspension.
The valves that transport abrasive fluids will have a useful life depending on the product that it transports and the quality and anti-abrasive behavior of the sleeves that are inside the valve housing. The higher the quality, the less downtime and lower maintenance cost.
Corrosion
Corrosion is the result of two elements reacting with each other and altering their characteristics. The damage suffered by valves due to corrosion occurs both inside and outside the valve, it is one of the most adverse effects and difficult to prevent in valves. Damage to valves due to corrosion occurs due to incompatibility between materials between the content and the container, temperature and pressure of the process, PH, concentrations and environment.
Even knowing these data, it is almost impossible to know for sure what the causes of the appearance of corrosion damage will be, since this can appear due to random triggers: calculation errors, the appearance of condensate under the insulation or leaks in the gasket.
Corrosion damage usually intensifies more where the corrosive fluid impacts with greater force, such as transition zones that generate splashes. Fully submerged or exposed areas are less susceptible to damage.
Corrosion is the result of two elements reacting with each other and altering their characteristics. Corrosion damage occurs both inside and outside the valve, it is one of the most adverse effects and difficult to prevent in valves
In mixture 1, as it is a homogeneous combination of materials, corrosion will attack slowly. However, in mixture 2, the opposite will happen. Although the corrosion is located in the border area, the phenomenon will attack the other material much faster.
Corrosive action intensifies in materials where the elements are not mixed, so when a gasket fails, ambient air mixed with the process fluid drastically accelerates the corrosion process in the transition zone of the valve stem.
Condensation
Condensation is the change of state of matter from a gas (usually steam) to a liquid. This liquid appears in the form of drops inside the valves that are projected at high speed, generating abrasion on the internal parts.
Corrosion damage tends to intensify more where the corrosive fluid impacts with greater force, such as areas of transition that generate splashes. Fully submerged or exposed areas are less susceptible to damage.
High speed
The narrowing of a section (such as a valve) increases the pressure and velocity of the fluid along of this section, excessive speed can damage the valve as well as produce vibrations and noise. Speed combined with other factors such as corrosion, abrasion or condensation can reinforce the impact very negatively. Speed damage is usually seen at the valve outlet forming striations or channels.
As a general rule, a speed limit is established that will prevent intolerable damage. This limit will depend on the characteristics of the fluid and the robustness of the valve. To give an example, in applications with water it is recommended not to exceed 10m/s, or 30m/s in steam.
Cavitation
Valves also suffer from cavitation damage. This effect is the opposite of condensation, it consists of the implosion of gas bubbles within the liquid fluid. To understand this phenomenon we must imagine a pressure curve that the fluid will follow as it passes through the valve.
The pressure in a circuit is always higher before the fluid passes through the valve. Once inside that section, a pressure rebound will occur, so it will be below the outlet pressure. If the pressure falls below the limit, cavitation will occur, the fluid will vaporize for an instant, generating gas bubbles that will release a large amount of gas. of energy drastically damaging the internals of the valve. Cavitation damage is clearly visible in the valve plugging medium.
Flashing
Flashing is an effect similar to cavitation only that it happens after the constraint. It is another of the damages suffered by the valves. This phenomenon is not avoidable, since it depends exclusively on the process conditions. As you can see in the graph, this time the limit for the vaporization of the fluid is too high to be avoided, so the liquid fluid will generate bubbles that will impact the outlet of the downstream valve.
The damage is similar to that generated by high velocity, only more devastating and always in the direction of the fluid.< br />So, what is the method to reduce this damage? Well, quite the opposite of cavitation, in this case we want the fluid to quickly cross the vena contracta without practically touching the internals of the valve. The best design in this case will be a valve with an outlet at an angle of 90º.
Degassing
This phenomenon occurs when the fluid is made up of a mixture of liquid with a dissolved gas of different molecular weights, normally in applications that are severe service in refining, petrochemicals and oil and gas. When the drop in pressure breaks the equilibrium between the liquid and the gas, the latter is released.
This process has a great potential for damage , since when the gas is released it suddenly increases the volume of the flow. If the flow area following the valve is not larger, the fluid velocity will increase. The restricted section can generate drops that will impact, eroding the inner parts of the valve, and can also generate vibrations and noise.
This problem can be solved with a correct resizing of the valves to accommodate the volumetric expansion of the flow.
And here we end with the damage suffered by the valves, which is not few! As you can see, it is important to carry out a good study to prevent strong> this type of effects, but remember that you are not alone, if you have a demanding industrial process, at risk of suffering one of these attacks, the GRM team will be happy to help you choose the best solution.
Damage that valves suffer and why
Can the valves get sick? Who or what causes valve damage?
A valve installed without regard to a method of protecting it from weather factors, such as a coating, can stop working long before the end of its useful life.
Environment damage
EXTERIOR DAMAGE THAT VALVES SUFFER
The valves can be attacked from outside, that is, damage that is not generated by the fluid that passes through them. In any process installation, it must be considered whether the valve is protected or exposed to the elements, whether there is dust, gases, humidity, whether the material of the body is compatible with the substances corrosive substances in the environment, live microorganisms, saline environments or condensation from the insulation itself. A valve installed without taking into account a method that protects it from weather factors, such as a coating, can stop working long before the end of its useful life.
To avoid these attacks we must carefully select the materials in contact with the outside of the valve and protect exposed areas such as pipes, actuators or positioners as well to carry out periodic maintenance.
Damage inside the valve
INTERNAL DAMAGE THAT VALVES SUFFER
The internal damage is produced by the fluid that passes inside and affects all the elements that they are in contact. In this section we are going to go into detail, since the valves can get sick due to various factors.
Abrasion
The speed and particles in suspension of an internal fluid cause a loss of the material that makes up the valve, which causes some parts to be more polished or worn than others, normally the points where the speed is higher, the sealing medium and the joints or seats.
Abrasion consists of the loss of material due to the impact of suspended particles.
The damage of abrasion will depend on the angle of incidence, the velocity of the fluid, the density and size of the particles in suspension.
The valves that transport abrasive fluids will have a useful life depending on the product that it transports and the quality and anti-abrasive behavior of the sleeves that are inside the valve housing. The higher the quality, the less downtime and lower maintenance costs.
Corrosion
Corrosion is the result of two elements reacting with each other and altering their characteristics. Corrosion damage occurs both inside and outside the valve, it is one of the most adverse effects and difficult to prevent in valves. Damage to valves due to corrosion occurs due to incompatibility between materials between the content and the container, temperature and pressure of the process, PH, concentrations and environment.
Even knowing these data, it is almost impossible to know for sure what the causes of the appearance of corrosion damage will be, since this can appear due to random triggers: calculation errors, the appearance of condensate under the insulation or leaks in the gasket.
Corrosion damage usually intensifies more where the corrosive fluid impacts with greater force, such as transition zones that generate splashes. Fully submerged or exposed areas are less susceptible to damage.
Corrosion is the result of two elements reacting with each other and altering their characteristics. Corrosion damage occurs both inside and outside the valve, it is one of the most adverse effects and difficult to prevent in valves
In mixture 1, as it is a homogeneous combination of materials, corrosion will attack slowly. However, in mixture 2, the opposite will happen. Although the corrosion is located in the border area, the phenomenon will attack the other material much faster.
Corrosive action intensifies in materials where the elements are not mixed, so when a gasket fails, ambient air mixed with the process fluid drastically accelerates the corrosion process in the transition zone of the valve stem.
Condensation
Condensation is the change of state of matter from a gas (usually steam) to a liquid. This liquid appears in the form of drops inside the valves that are projected at high speed, generating abrasion on the internal parts.
Corrosion damage tends to intensify more where the corrosive fluid impacts with greater force, such as areas of transition that generate splashes. Fully submerged or exposed areas are less susceptible to damage.
High speed
The narrowing of a section (such as a valve) increases the pressure and velocity of the fluid along of this section, excessive speed can damage the valve as well as produce vibrations and noise. Speed combined with other factors such as corrosion, abrasion or condensation can reinforce the impact very negatively. Speed damage is usually seen at the valve outlet forming striations or channels.
As a general rule, a speed limit is established that will prevent intolerable damage. This limit will depend on the characteristics of the fluid and the robustness of the valve. To give an example, in applications with water it is recommended not to exceed 10m/s, or 30m/s in steam.
Cavitation
Valves also suffer from cavitation damage. This effect is the opposite of condensation, it consists of the implosion of gas bubbles within the liquid fluid . To understand this phenomenon we must imagine a pressure curve that the fluid will follow as it passes through the valve.
The pressure in a circuit is always higher before the fluid passes through the valve. Once inside that section, a pressure rebound will occur, so it will be below the outlet pressure. If the pressure falls below the limit, cavitation will occur, the fluid will vaporize for an instant, generating gas bubbles that will release a large amount of gas. of energy drastically damaging the internals of the valve. Cavitation damage is clearly visible in the valve plugging medium.
Flashing
Flashing is an effect similar to cavitation only that it happens after the constraint. This phenomenon is not avoidable, since it depends exclusively on the process conditions. As you can see in the graph, this time the limit for the vaporization of the fluid is too high to be avoided, so the liquid fluid will generate bubbles that will impact the outlet of the downstream valve.
The damage is similar to that generated by high velocity, only more devastating and always in the direction of the fluid.< br />So, what is the method to reduce this damage? Well, quite the opposite of cavitation, in this case we want the fluid to quickly cross the vena contracta without practically touching the internals of the valve. The best design in this case will be a valve with an outlet at an angle of 90º.
Degassing
This phenomenon occurs when the fluid is made up of a mixture of liquid with a dissolved gas of different molecular weights, normally in applications that are severe service in refining, petrochemicals and oil and gas. When the drop in pressure breaks the equilibrium between the liquid and the gas, the latter is released.
This process has a great potential for damage , since when the gas is released it suddenly increases the volume of the flow. If the flow area following the valve is not larger, the fluid velocity will increase. The restricted section can generate drops that will impact, eroding the inner parts of the valve, and can also generate vibrations and noise.
This problem can be solved with a correct resizing of the valves to accommodate the volumetric expansion of the flow.
And here we end with the damage that the valves can suffer, which is not few! As you can see, it is important to carry out a good study to prevent< /strong> this type of effects, but remember that you are not alone, if you have a demanding industrial process, at risk of suffering one of these attacks, the GRM team will be happy to help you choose the best solution
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