When is brazing of tubes-to-tubesheet is done?

Brazing is done when the stress concentration and the crevice corrosion cannot be tolerated, but neither the temperature is very high nor is the possibility of leakage of one fluid into the other is hazardous.

It is generally preferred only in cases where welding cannot be done, such as joining dissimilar materials such as aluminum and steel. Since the brazing alloys (copper, copper alloys, aluminum alloys, etc.) are brittle, no welding can be done close to a brazed joint because the heat and/or the thermal stresses due to welding may crack the brazed joint.

What harm does hydrogen cause to carbon steel? What materials should be used if hydrogen is present?

Carbon in steel combines with hydrogen to form methane and other products under high pressure and temperature (above 200 degrees C or 390 degrees F). This first results in decarburization followed by localized fissuring of the vessel due to high gaseous pressure, leading to the failure of the vessel.

Chromium- and molybdenum-containing steels are best suited for use with hydrogen. They resist decarburization, fissuring, and the associated loss of strength.

What is the difference between IRON and STEEL?

Iron, in industrial terminology, generally refers to cast iron, which is an alloy of elemental iron and carbon.
Steel is refined form of iron with carbon in solution as Fe3C, while cast iron has carbon in the form of graphite besides that in the solution, which gives it non-uniform structure and makes it brittle.

When is welding of tubes-to-tubesheet is done?

A simple rolled tube-to-tubesheet joint may spring a leak due to fatigue or stress relaxation. Welding is done for more leak-tightness and for high-temperature operations.

Oppose Efforts to Impose New Tax Burdens on the Internet | eBay Main Street – Public Policy and Breaking Ecommerce News

Oppose Efforts to Impose New Tax Burdens on the Internet | eBay Main Street – Public Policy and Breaking Ecommerce News.

What are the affects of tube material on the performance of heat exchanger?

Type material has the following effects on the performance of heat exchanger:

-          Resistance to corrosion, erosion, and vibration damage (natural frequency of the tube)

-          Thermal stresses induced due to differential thermal expansion of the tube bundle and the shell

-          Extent of fouling

-          Extent of microbial deposit

-          Resistance to heat transfer

-          Ease of joining tubes to the tubesheet

-          Cost and weight of the unit, etc.

What materials are used for tubes in saltwater coolers?

Salt water can be brackish, brine, or sea water, the last being used a lot in coolers and condensers in plants on the sea coast. Titanium is widely used for saltwater coolers. Aluminum bronzes are also used if there are no pollution.

Which types of steel can be used for high-temperature service?

There are basically 4 different types of steel used for high-temperature service:

• Carbon steels – for most usage up to 750 degrees F (400 degrees C). Carbon steels are cheaper, very strong, with highest thermal conductivity. Above 750 degrees F, their creep increases; above 950 degrees F (510 degrees C) they get oxidized too.
• Chromium-molybdenum steels – resist oxidation up to 1200 degrees F (650 degrees C). But their thermal conductivity is lower; and chromium-molybdenum steels are more expensive than carbon steels.
• Ferritic stainless steels – can be used up to 1500 degrees F (820 degrees C).  Ferritic stainless steels have higher thermal conductivity, lower thermal expansion coefficient, and less expensive than other materials for the same service. Ferritic stainless steels can resist oxidation as well as attack from sulfur- and carbon-containing flue gases. Coefficient of thermal expansion of ferritic stainless steels is lower than for austenitic stainless steels. Loose strength after a very long usage at high temperatures.
• Austenitic stainless steels – the strongest among steels for use at high temperatures and do not loose strength after very long usage at high temperatures. Austenitic stainless steels resist oxidation at high temperatures and are widely used in boilers, super-heaters, refinery services, etc., where chlorine is not present.

What is an ALLOY STEEL?

It is steel that contains, besides carbon, one or more of the following materials:

• Aluminum
• Boron
• Chromium
• Cobalt
• Manganese
• Molybdenum
• Nickel
• Niobium
• Silicon
• Titanium
• Tungsten
• Vanadium
• Zirconium, etc.

Each of these alloying elements affects the properties of steel. The amount of added elements depends on the end use of the steel.

What factors generally cause mechanical failure of heat exchangers?

Among the several factors that can cause mechanical failure of heat exchangers, both of PHEs and shell-and-tube, are:

• Corrosion of parts
• Excessive thermal or mechanical stresses acting alone or in combination
• Unexpected seismic load
• Vibration
• Inferior workmanship and poor inspection
• Defective or unsuitable materials of fabrication
• Poor maintenance