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Inspectioneering Journal

Results of Degassing of Refinery Steel Components Prior to Welding

Some Field Observations - Part 1

This article appears in the May/June 1997 issue of Inspectioneering Journal

Case 1: Fuel Gas to boilers in boiler house: in 1992 two flanges were installed for installation of knock blinds. No degassing was completed. Both welds were radiographed and noted as acceptable. The pipe was 3" and a 250 degree preheat was used.

Case 2: Alky Unit Flare Header: No degassing completed in 1993 on multiple tie-ins. All of these tie-ins were radiographed and noted as acceptable. The size of pipe was 6", 10", 12" and a 250 degree preheat was used.

Case 3: Fuel gas to FCCU Heater: in 1994 modifications to the fuel gas lines were completed. Tie-ins were completed at the heater. The radiographs showed major areas of gas pockets and were rejected. Rosebud degas along with elevated preheat and interpass temperatures of 400F - 500F were used unsuccessfully. Entire welds had to be ground out and repaired in order to qualify these welds. Pipe size was 4".

Case 4: Flare piping downstream and within 100 feet of piping of the Wet Gas Compressor in the FCCU. No degas was performed prior to any welding in 1994 modifications to the system. All radiographs were noted as rejectable. All piping had to be replaced between flanges. Degas could have been done but replacement between flanges was less expensive. Piping sizes were 6", 4", and 3".

Case 5: Fuel Gas to Platformer and Hydrobon Heaters: Modifications were made on all heaters in the platformer and the hydrobon piping systems. Tie-ins were radiographed and 50% were noted as rejectable. Elevated preheat and interpass temperatures of 350F-400F were used unsuccessfully. The gas pockets were isolated and eventually removed at extra cost.

Case 6: 4" waste gas from seal drum to vacuum heater line in the crude unit, 4" line.

A section of piping was replaced in August of 1994. Tie-in points (field welds) were not degassed prior to welding. Both welds were radiographed and noted as rejectable. The two field welds were then degassed according to a controlled degassing procedure, replaced, re-radiographed and noted as acceptable.

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