Testing Method for Stainless Steel Flange Butt Welding Ring Material - Manufacturer of Wholesale Aluminum Pipe Flanges

50. Sulfuric acid test

The sulfuric acid immersion test for stainless steel flange butt welding rings can differentiate between 302 and 304 stainless steels from 316 and 317. The cut edge of the sample should be finely ground, then cleaned and passivated in nitric acid (specific gravity 1.42) with a volume concentration of 20~30% and a temperature of 60~66 ℃ for half an hour. The volume concentration of the sulfuric acid test solution is 10% when heated to 71 ℃. When 302 and 304 steel sheets are immersed in this hot solution, they rapidly corrode and produce numerous bubbles, with the samples turning black within a few minutes. Conversely, the samples of 316 and 317 steel do not corrode or react significantly (without bubbles), and their color remains unchanged within 10-15 minutes. For increased accuracy, simultaneous testing of samples with known compositions can facilitate a more precise comparison.

50. Copper sulfate point test

The copper sulfate spot test is a straightforward method to rapidly distinguish between ordinary carbon steel and all types of stainless steel. A copper sulfate solution with a concentration of 5-10% is used for this test. Before conducting the spot test, ensure that the test area is thoroughly cleaned of grease or impurities, and a small area should be polished with a soft abrasive cloth. Then, drip the copper sulfate solution into the cleaned area using a dropping bottle. Ordinary carbon steel or iron will form a layer of surface metal copper within a few seconds, while the surface of stainless steel will not produce copper precipitation or exhibit a copper color.

50. Magnetic test

A magnetic test is a straightforward method to distinguish between annealed austenitic stainless steel and ferritic stainless steel. Austenitic stainless steel is typically non-magnetic, but it may exhibit slight magnetism after cold working under high pressure. In contrast, pure chromium steel and low-alloy steel are known for being strongly magnetic.

50. Nitric acid point test

A notable characteristic of the stainless-steel flange butt welding ring is its inherent corrosion resistance to concentrated and dilute nitric acid. This property facilitates its easy differentiation from most other metals or alloys. However, high-carbon 420 and 440 steel sheets may experience slight corrosion during the nitric acid spot test, while non-ferrous metals will corrode immediately upon contact with concentrated nitric acid. Dilute nitric acid is highly corrosive to carbon steel.

How to Assemble and Weld Stainless Steel Flanges

Preparing a flange guiding rule or square is essential for assembling and welding stainless steel flanges. The requirement is that the longitudinal centerline of the pipe be perpendicular to the end face of the stainless steel flange.

During assembly, place the stainless-steel flange onto the pipe end, ensuring the pipe end overlaps by more than half of the flange thickness but doesn't exceed the plane of the end face. Then, a flange guiding rule will be used to check whether the upper and lower-end faces are perpendicular. If they are nearly aligned, spot weld the upper end with electric welding and rotate it 180 degrees. Recheck for alignment; if necessary, use a hammer to knock and align it until it's perfectly vertical. Once it's vertical, spot-weld it again. Alternatively, spot weld two points on the other two opposite sides for formal welding. For smaller flanges, spot welding at three points may suffice.

When using a square, measuring whether the outer surface of the stainless-steel flange and the pipe wall are perpendicular is crucial. The diagonal alignment method is also employed for assembly. It's worth noting that the outer surface of the stainless-steel flange must be parallel to the end face to ensure accurate measurements. During welding of the stainless-steel flange with the pipe, consider the allowable inclination of the flange and the permissible deviation of the screw hole position.

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