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How to radiographic test for welding quality in your heat exchanger

Posted by Krista Drager on 4/19/16 4:20 PM

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Sample coolers and heat exchangers cool samples from process streams. A sample flows through the tube side of the heat exchanger, and the cooling fluid, usually water, flows through the shell side to cool the process gas or fluid so it can be monitored or analyzed.

Sample coolers and heat exchangers generally range from one to five square feet of heat transfer surface and have different purposes. For reasons of safety and efficiency, it is important that the right product is used for the right application, considering specific type of gas or fluid, temperature, pressure and flow conditions.

Choose the right base heat exchanger for your unique application

A wide variety of industries around the globe use sample coolers and heat exchangers. Occasionally, these products need specialty testing such as radiographic testing of weld joints to ensure quality. When selecting a heat exchanger base model, consider your application specifications so you can choose the correct product materials for flow, viscosity, pressure and temperature.

For instance, a U.S. facility required a pair of spiral heat exchangers. For efficiency and durability, each heat exchanger featured 20 tubes that were 3/8-inch and 316 stainless steel in a 16-inch diameter 304 stainless steel shell. On the surface, this was a fairly typical spiral heat exchanger with ASME certification.

Check product certifications to ensure quality from the start

American Society of Mechanical Engineers (ASME) certification tells customers that the strength, chemical composition, and pressure testing and ratings of a product’s materials comply with the strictest industry quality mandates. An ASME Code manufacturing facility will manufacture products that receive the Pressure Vessel designation (the “U” stamp), guaranteeing their alignment with written ASME procedures, specifications and test requirements.

Unique test: Radiographic examination of heat exchanger proves quality

To ensure quality, you may require a radiographic examination of the weld joints between the heat exchanger spiral manifolds and special connection fittings. Radiographic testing involves taking an x-ray of the welds to ensure there is no porosity or cracks. A Level III NDE (non-destructive examination) inspection may be required to approve the radiographs prior to proceeding with product finalization.

After the radiography examination, a “sensitive leak test” may be performed. This requires pressurizing the coil assembly with helium and using an ultrasensitive helium detector to ensure there were no leaks in the coil assembly. The analyzer can detect a helium leak that is the equivalent of 1x10-9 cc per second. At this miniscule leak rate, it would take about 30 years to fill only a one cubic centimeter volume.

Certain companies specialize in these two tests. Once the high-quality welding work on the heat exchangers passes the coil assembly test, you can be confident of the product performance and quality and thus, time and money savings.

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Topics: Power, Hydrocarbon Processing, Any Application

Written by Krista Drager

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