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51317--9623-Are Drill Pipe Conventional Coatings Suitable for Subsea Early Production Risers?

This paper presents failures of the internal coating of drill pipe riser (DPR) systems that operated for 8 months in extended well testing (EWT) in Brazilian pre-salt fields at 1900-m sea depth. After two different EWT operations, blisters were seen through the internal coating of tubes that had been in service.

Product Number: 51317--9623-SG
ISBN: 9623 2017 CP
Author: Rodrigo Barreto
Publication Date: 2017
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Drill pipe (DP) materials and corrosion protection methods have been designed for a specific envelop of drilling operational characteristics concerning stress level temperatures (high) and fluids (mud). Changing the functionality of DP from drilling operation to completion operation with early production in a subsea environment requires a good critical analysis since the typical internal coating designed for the mud abrasive and erosive actions may not be suitable for exposure to the potentially corrosive production fluids.This paper presents failures of the internal coating of drill pipe riser (DPR) systems that operated during eight months in extended well testing (EWT) in Brazilian pre-salt fields at 1900 meters sea depth. After two different EWT operations blisters were seen through the internal coating of the tubes which had been in service. Visual inspection was carried out on a sampling of the tubes that operated in different positions of the string along the water depth in order to characterize and to provide an assessment about the damage found on the internal coating.An investigation was conducted and the coating disbondment was found to be associated with hydrogen blistering and the intensity of blistering increased with the water depth. Hydrogen was generated by the cathodic protection from sacrificial anodes distributed on the wellhead stack-up frames crossing through the wall of the tubes from the external to the internal side and emerging as bubbles under the internal coating. Temperature has been considered as a major catalysis factor of the process and the adherence of the coating onto the metallic substrate determined the size and severity of hydrogen blisters. The conclusion was that even when a good epoxy coating is specified for corrosive protection it may not be compatible with the subsea hydrogen charging due to cathodic protection generated by the connection of the column into a subsea structure.

Key words: blistering, cathodic protection, thermal gradient, internal plastic coating (IPC), drill pipe riser, early production riser, sour service, SSCo

 

Drill pipe (DP) materials and corrosion protection methods have been designed for a specific envelop of drilling operational characteristics concerning stress level temperatures (high) and fluids (mud). Changing the functionality of DP from drilling operation to completion operation with early production in a subsea environment requires a good critical analysis since the typical internal coating designed for the mud abrasive and erosive actions may not be suitable for exposure to the potentially corrosive production fluids.This paper presents failures of the internal coating of drill pipe riser (DPR) systems that operated during eight months in extended well testing (EWT) in Brazilian pre-salt fields at 1900 meters sea depth. After two different EWT operations blisters were seen through the internal coating of the tubes which had been in service. Visual inspection was carried out on a sampling of the tubes that operated in different positions of the string along the water depth in order to characterize and to provide an assessment about the damage found on the internal coating.An investigation was conducted and the coating disbondment was found to be associated with hydrogen blistering and the intensity of blistering increased with the water depth. Hydrogen was generated by the cathodic protection from sacrificial anodes distributed on the wellhead stack-up frames crossing through the wall of the tubes from the external to the internal side and emerging as bubbles under the internal coating. Temperature has been considered as a major catalysis factor of the process and the adherence of the coating onto the metallic substrate determined the size and severity of hydrogen blisters. The conclusion was that even when a good epoxy coating is specified for corrosive protection it may not be compatible with the subsea hydrogen charging due to cathodic protection generated by the connection of the column into a subsea structure.

Key words: blistering, cathodic protection, thermal gradient, internal plastic coating (IPC), drill pipe riser, early production riser, sour service, SSCo

 

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