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PRCI PR-75-9714
- Damage to FBE and Liquid Epoxy Coating from Hydrogen Outgassing from Welds
- Report / Survey by Pipeline Research Council International, 05/26/2004
- Publisher: PRCI
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L51903e
Case Western Reserve University
Need: Hydrogen in welds and its affect on performance from the perspective of cracking and embrittlement of steels has been widely studied, and welding procedures have been developed to minimize the deleterious effects of hydrogen. The practical problem is whether hydrogen outgassing from welds causes damage to FBE and liquid epoxy coatings on pipelines. FBE coatings on longitudinal welds made at pipe mills have developed defects because of hydrogen outgassing. Field welds are often coated shortly after welding, inspected and either buried or submerged, and there is a greater chance for more hydrogen in the field welds than mill welds. If coating damage occurred by outgassing, the damage could go undetected and affect the pipeline corrosion control.
Result: The objectives were to examine hydrogen outgassing as a cause of damage to FBE and liquid epoxy coatings, to collect and contrast experience with hydrogen in longitudinal welds and circumferential welds, to quantify hydrogen pickup and release from steel pipe and welds. Methods and practices are identified to avoid damage to FBE and liquid epoxy pipeline coatings from hydrogen outgassing. The approach was to examine epoxy coatings applied over welds for damage from hydrogen outgassing and to conduct experiments to determine the amount and rate of hydrogen desorption (outgassing) from welds. The effects of hydrogen desorption on coatings was examined for commercial FBE and liquid epoxy coatings along with screening tests with liquid glycerol and clear epoxy. Hydrogen desorption was measured directly on welds, and a model was developed to describe the outgassing of diffusible hydrogen and the amount of diffusible hydrogen remaining in the weld.
Benefit: The likelihood of hydrogen damage to coatings depends upon the amount of hydrogen that is introduced into the weld by the weld consumable and welding process, the holding time after welding and prior to coating, and any surface treatment or thermal treatment applied after completion of the weld and prior to coating. Hydrogen permeation was evaluated as a function of weld consumable and location/orientation in the weldment. A model was developed for hydrogen desorption from welds in order to understand the hydrogen movement within the weld metal. Hydrogen desorption from welds as well as diffusible hydrogen remaining in welds was evaluated as a function of time. Three weld consumables were used to examine a range of weld hydrogen levels.
Case Western Reserve University
Need: Hydrogen in welds and its affect on performance from the perspective of cracking and embrittlement of steels has been widely studied, and welding procedures have been developed to minimize the deleterious effects of hydrogen. The practical problem is whether hydrogen outgassing from welds causes damage to FBE and liquid epoxy coatings on pipelines. FBE coatings on longitudinal welds made at pipe mills have developed defects because of hydrogen outgassing. Field welds are often coated shortly after welding, inspected and either buried or submerged, and there is a greater chance for more hydrogen in the field welds than mill welds. If coating damage occurred by outgassing, the damage could go undetected and affect the pipeline corrosion control.
Result: The objectives were to examine hydrogen outgassing as a cause of damage to FBE and liquid epoxy coatings, to collect and contrast experience with hydrogen in longitudinal welds and circumferential welds, to quantify hydrogen pickup and release from steel pipe and welds. Methods and practices are identified to avoid damage to FBE and liquid epoxy pipeline coatings from hydrogen outgassing. The approach was to examine epoxy coatings applied over welds for damage from hydrogen outgassing and to conduct experiments to determine the amount and rate of hydrogen desorption (outgassing) from welds. The effects of hydrogen desorption on coatings was examined for commercial FBE and liquid epoxy coatings along with screening tests with liquid glycerol and clear epoxy. Hydrogen desorption was measured directly on welds, and a model was developed to describe the outgassing of diffusible hydrogen and the amount of diffusible hydrogen remaining in the weld.
Benefit: The likelihood of hydrogen damage to coatings depends upon the amount of hydrogen that is introduced into the weld by the weld consumable and welding process, the holding time after welding and prior to coating, and any surface treatment or thermal treatment applied after completion of the weld and prior to coating. Hydrogen permeation was evaluated as a function of weld consumable and location/orientation in the weldment. A model was developed for hydrogen desorption from welds in order to understand the hydrogen movement within the weld metal. Hydrogen desorption from welds as well as diffusible hydrogen remaining in welds was evaluated as a function of time. Three weld consumables were used to examine a range of weld hydrogen levels.
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