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USED BOILERS

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A. Las calderas de tubos de humo también llamadas pirotubulares tienen una vida útil promedio de hasta 30 años, siempre y cuando se operen correctamente. Se tienen que hacer mediciones continuas de sus cifras de combustión y un riguroso control del agua de la caldera (tratamiento químico correcto de agua). La vida útil de la caldera se recorta drásticamente cuando ha
sufrido daños en su hogar (o tubo cañón) y en sus espejos por bajo nivel de agua.

El envolvente del cuerpo de presión de la caldera (cuerpo de la caldera) sufre a través del tiempo pérdidas del espesor requerido, sobre todo en los puntos cercanos a la salida de vapor y la
entrada de agua por erosión y corrosión interna.

Evaluating a Used Boiler La única forma correcta para poder determinar la presión máxima de trabajo de una caldera usada, es por medio de la medición de espesores por ultrasonido (un método relativamente económico y seguro), con más de 50 mediciones en el envolvente de la caldera y tomando especial cuidado de medir espesores en las periferias (5 a 40 cms.) de los coples:

• Steam exit.
• Water feed.
• Bottom blowdowns.
• Surface blowdowns.

The critical minimum thickness of the boiler shell can thus be detected and based on this measurement, the maximum allowable working pressure of a used boiler can be calculated.

Lo anterior es únicamente en relación con el envolvente del cuerpo de presión de la caldera, pero la caldera en su operación tiene partes más críticas y más expuestas a desgaste como lo es el tubo cañón u hogar, que recibe a la flama del quemador.

The furnace, which is directly exposed to the burner flame during operation, is an even more critical component to the longevity of a used boiler. Los continuos cambios de temperatura pasando de “apagado, a flama alta, flama baja, apagado” y con la noble obligación del acero de absorber las expansiones y contracciones, por consiguiente,

La fatiga del material del tubo cañón u hogar se da por antigüedad (tiempo), por falta de agua o recalentamiento, por un mal tratamiento de agua o una falla en el control de nivel de agua de la caldera.

En cuanto a la operación de la caldera usada, ésta dependió en sus años pasados de la correcta operación de sus controles de seguridad y el manejo correcto o incorrecto del operador de la misma a través del tiempo. Una falla por bajo nivel de agua, causó una tremenda fatiga en el tubo cañón u hogar de la caldera, dañó la resistencia del material del hogar y de los espejos, bajando considerablemente su restante vida útil sin poder detectar físicamente el daño en el cuerpo de presión. Lo mismo sucede con un torito o falsa explosión. El verdadero estado de la calderausada lo conoce únicamente el usuario a través del tiempo. (Obviamente cuando nos quieren vender una caldera usada, el vendedor dice que casi nunca operó y que por lo tanto sus años de operación antiguos son de uno o dos. Nos “cuenta” que nunca tuvo bajos niveles de agua, que nunca tuvo explosiones y que su sistema de controles está en “casi” perfectas condiciones, lo cual lamentablemente nunca es cierto).

You get what you pay for, as the saying goes, with used boiler purchases, with “great deals” often turning out to be extremely expensive because of costly repairs. ya que una reparación mayor no solamente es sumamente costosa, sino que adicionalmente no es recomendable porque el cuerpo de presión nunca volverá a ser el mismo. En el cambio de un espejo o tubo cañón, el corte y la soldadura dañan al material viejo fatigándolo en exceso y aumentando el riesgo de la futura operación de la caldera).

Changing the tubes will not extend the useful life of the other components of the boiler. Los tubos flux son parte del material que se debe cambiar en una caldera periódicamente durante su tiempo de vida útil. The frequency of the tube changes depends on the gauge of the tubes and the water quality control of the boiler.

The bottom line is it does not matter how a used boiler looks, if it has a new lining and tubes or no. What matters in terms of the useful life of a (used) boiler is the condition of the pressure body – the shell (more specifically its critical thickness), the furnace, and the tube sheets.

B. In our neighboring country united States of America, changed the boiler more frequently (at a younger age), because the insurance increase your premiums significantly every year from the seventh year. (A new boiler patterned pay a lot less insurance premium to a boiler similar to 10 years of age).

Rarely are we going to find boilers in operation with more than 20 years of age, in companies and prestigious institutions in U. S. A.

In addition, the americans have buyers of boilers used (considered junk), in the markets of Mexico and Central america.

Existen empresas en U.S.A. que se dedican a comprar calderas usadas como chatarra, les cambian el forro y los tubos flux y las ofrecen a sus países vecinos del Sur como calderas semi-nuevas con muy poco uso real, lo cual nunca es cierto ni comprobable.

• A cauldron of smoke tubes with an age of 5 to 7 years is a boiler, semi-new used.

• A boiler with an age of 15 years or more, is a caldera junk that you no longer should buy or sell for high risk.

We emphasize: No importa como se ve la caldera, si tiene un forro nuevo o no, o si tiene tubos flux nuevos o no. Lo que importa en la vida útil de una caldera usada es su cuerpo de presión: su envolvente – thickness critical –her home , the tube or barrel and its mirrors.

C. A new boiler, equipped with a high efficiency burner, is ecological, Consume menos combustible que una caldera usada. Normalmente con el ahorro de combustible de la nueva caldera, su costo de adquisición quedará amortizado en muy poco tiempo.

Una caldera nueva trabajando 24 horas se paga en año y medio por los ahorros de combustible. De esta forma, genera posteriormente grandes ahorros a través del tiempo una vez que se ha amortizado el costo inicial de la inversión.

While a simple price comparison between new and used boilers may lead to the conclusion that a used boiler is the cost-effective way to go, such a surface-level analysis does not provide information required to make a truly informed decision.

Fire tube boilers have an average useful life of up to 30 years, but only if they are operated correctly, undergo continuous review of their combustion figures, and count on a rigorous control and treatment of their feedwater. The useful life of a fire tube boiler is dramatically shortened when it suffers damages to its furnace and tube sheets because of low water levels, scaling or thermal shock. For this reason, it is extremely critical to know how to evaluate the current condition of a boiler before making a used boiler purchase.

Evaluating a Used Boiler

The shell of the boiler, for example, suffers a loss of its required thickness with time. This loss is most acutely observed in the points closest to the steam exit and water entrance due to erosion and internal corrosion. Reduced thickness at any point in the shell of the boiler body means a decline in the pressure at which the boiler can be operated.

One way to determine the maximum allowable working pressure (MAWP) of a used boiler is by measuring wall thickness via ultrasound. This technique is relatively safe and cost-effective, and should be performed on at least 50 points of the boiler shell, including the periphery of the couplings:

• Steam exit
• Water feed
• Bottom blowdowns
• Surface blowdowns

The critical minimum thickness of the boiler shell can thus be detected and based on this measurement, the maximum allowable working pressure of a used boiler can be calculated.

The previous method can be applied only to the shell of the boiler, however this is not the only part of the boiler that can experience wear from use.

The furnace, which is directly exposed to the burner flame during operation, is an even more critical component to the longevity of a used boiler. It is exposed to the greatest amount of material fatigue over time as its steel frame absorbs the expansions and contractions caused by temperature changes (from “off” to “ high flame” to “low flame” to “off” for example).

The material fatigue of the furnace is produced by use over time but can also be caused by a lack of water or overheating; by poor water treatment; or by a defect in the boiler water level control.

With respect to the operation of a used boiler, this depends on the care with which it was run in the past – on the correct operation of its security controls and on the correct (or incorrect) handling of the boiler by its operator.

As discussed previously, a failure caused by low water level produces a tremendous amount of material fatigue in the furnace, thus reducing the material resistance of both the furnace and the tube sheets and considerably shortening the remaining useful life of the boiler. Unfortunately, this type of defect does not result in physical damage to the pressure body of the boiler and is not, therefore, easily detected. This is the same case for small explosions inside the combustion chamber.

The true condition of a used boiler can only be ascertained by its previous owner. Some used boiler salespersons will state that the boiler was hardly ever operated, never had low water levels or explosions, and that its control system is in “almost perfect” condition; unfortunately, this is almost never the case but will be hard to prove.

You get what you pay for, as the saying goes, with used boiler purchases, with “great deals” often turning out to be extremely expensive because of costly repairs. These repairs, moreover, are not recommendable because the pressure vessel of the boiler will never return to its previous top condition, as changing a tube sheet or furnace causes damage to the old material (via the cutting and welding), further wearing it out and increasing the risk to the future operation of the boiler.

Changing the tubes will not extend the useful life of the other components of the boiler. The tubes represent a part of the material of the boiler that should be changed periodically throughout its useful life. The frequency of the tube changes depends on the gauge of the tubes and the water quality control of the boiler.

The bottom line is it does not matter how a used boiler looks, if it has a new lining and tubes or not. What matters in terms of the useful life of a (used) boiler is the condition of the pressure vessel – the shell (more specifically its critical thickness), the furnace, and the tube sheets.

Benefits of New Boiler

A new boiler, equipped with a high efficiency burner, is much more efficient, consuming considerably less fuel than a used boiler. In fact, the acquisition cost of a new boiler is generally amortized by the fuel savings after very little time. The cost of a new boiler will pay itself back with the fuel savings, in about a year and a half. After that, the benefit to the owner is pure fuel cost savings over the rest of the useful life of the new boiler.

These impressive savings, coupled with the reduced risk of operational issues and the security of knowing with clarity both the current condition and expected useful life of your capital investment make purchasing a new boiler worth the additional upfront cost.