Breakthrough of riser repairs

Until now Riser repairs has been a time consuming operation with reduced possibilities of extended lifecycles. Now a new process has been developed for Workover Risers in a joint venture between FMC Kongsberg Subsea AS and Scana Offshore Vestby AS.

The Scana Riser Repair Program provides the following advantages:

• Improved resistance against scratches and wear
• Improved resistance against corrosion and erosion
• Extended lifetime and service interval/cost
• Significantly reduced turn around time of repair (reduced time out of service).

The development project was initiated as a follow up of the repair/upgrade work carried out by Scana Offshore Vestby on Ormen Lange Risers for FMC Kongsberg Subsea AS during the autumn 2008. The purpose of the project was to improve the repair/upgrade processes for work over risers.

The project included:

• Development of new process for tungsten carbide coating inside the riser box end
• Development of new process for Inconel 625 coating of seal groves on riser pin end
• Documentation of existing process for tungsten carbide coating of pin end on annulus pipe

The new processes developed with tungsten carbide and Inconel 625 coating will reduce cost of maintenance significantly.

The coating process includes the following steps:

• Measurement control before machining
• Pre machining off existing coating to clean material
• NDT (Liquid penetrant testing) of ground material
• Thermal coating to required thickness
• Post machining according to specified inside diameter and tolerances
• Pressure testing
• NDT (Liquid penetrant testing) of coating
• Final measurement control

New Scana pre machining and post machining processes
In order to save time during the repair process SOV has developed special tools to pre machine and post grind the seal surface of the box end and pin end. The new processes are particularly beneficial for long risers where other methods of machining require significant time to align the riser. This significantly reduces the time required to coat the box end and pin end on the riser.

Choice of coating material and spray programme
When the seal surface in the riser box end is pre-machined, the diameter is measured and the necessary thickness of the coating is established. The choice of material and coating programme is determined by the necessary coating thickness.

A successful FAT and gas leak test was done by FMC Kongsberg Subsea AS.

Experience
Scana Offshore Vestby AS has a long track record of coating with Inconel and Tungsten carbide on products like rods in different sizes and pin ends.

Contactperson at Scana Offshore Vestby AS
Mr. Per Kristian Gabler, Mobile: +47 91737374, e-mail: pkg@scana.no