Published on 28 January 2013
When one of the Middle East's leading oil and gas operators discovered corrosion damage on the internal surface and in the sandwash nozzles of two of its high pressure separator vessels it required a prompt response.
The damage was mainly located in the dish head and vessel shell. As a temporary measure, in one instance, a nozzle with a blind flange was attached to the external side covering the corroded area.
The purpose of the nozzle was to prevent leakage in the event of the corrosion continuing through the vessel wall thickness.
A plant shutdown was scheduled for September 2005. The operator approached TWI in October 2004 requesting technical support for their intention to implement a permanent repair by weld overlaying the corroded areas.
TWI provided method statements and procedure qualification recommendations for:
- Weld repair of corrosion damage to the dish and shell plates using controlled deposition repair technique.
- Replacement/repair of corroded sandwash nozzles.
- Repair of corrosion damage by complete removal of the damaged dished end and shell section and inserting a flush insert plate into the vessel wall.
- Repair of corrosion damage to the nozzles by inserting a replacement nozzle using a flush insert plate into the vessel wall.
TWI reviewed qualification records for welders and procedures from the contractor hired by its client to carry out the repairs. This was followed by a visit during the shutdown to the offshore platform.
TWI spent three days on site offshore carrying out inspection of the repaired vessels and represented its Industrial Member in technical discussions with the underwriters and contractors in finalising the repair strategy.
The vessels were 100% visually inspected from inside, all damage mapped out and the repair for individual areas discussed and agreed in a final onshore review meeting.
TWI then provided technical support from UK. The repairs were carried out witnessed by the Authorised Inspector from the underwriter.
Following the successful repair of these two fabrications two further vessels were repaired using the same methodologies with witnessing by the same sub contractors and underwriters.
For information about TWI's capabilities please contact us.