Currently conducting (Automatic GMAW+P) weld metal build up repairs on the inside of a heat exchanger. Material is SA516-70 (¾" thick). Surface was sand blasted & a hydrogen bake out @ 500⁰F for two hours was completed before welding. Final weld repair location was inspected using liquid penetrant (PT) no relevant indications. First layer was welded surface was ground to smooth surface. PT inspected with no relevant indications noted. Second layer was welded & same surface prep & inspection (PT) as the first layer with no relevant indications. When Tube bundle was installed it was noted there was not enough clearance we were requested to remove some additional weld metal @ this time there were porosity indications noted after more grinding there is now significant porosity. During the welding there were no indications of porosity & the machine also has a low gas sensor. This vessel has been in service for thirty years. Service Shell Side-Hydro Carbons (Naphtha), Operating Shell side 200psig @ 650⁰F. I am thinking there may be an issue with the base metal. Graphitization possibly.
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SA156-70
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