Matt Dalton Transocean Offshore Deepwater Drilling Inc. (Gulf Coast Region)
Division Engineer 1311 Broadfield Blvd. Suite 400
Houston, TX 77084.
To : Eddy Redd
Cc : Logan Puckett, Thomley, Donnie
From : Matt Dalton
Date : 10th May 2001
Subject : Report - Deepseas Riser Tensioner Rod P1 Repair.
Reference : DDS-8597
In mid April 2001, tensioner rod P1 began leaking fluid. It was taken out of service until the next rig move on 3rd May 2001.
This rod was found to have coating failure during inspection on the last rig move on 26th March 2001. A patch repair was performed approximately 6" x 10" in size.
As Hydralift had a damaged rod at their facility for repair, they were requested to bring in a machining company (NTI) with the idea to remove the original coating all the way around the rod and perform a test piece for machining after coating, instead of hand finishing. Unfortunately, Hydralift did not instruct the coating company (National Thermospray) to remove the coating right round the rod, but only a patch. But the final result was good.
National Thermospray was mobilized to the Deepseas prior to the BOP being retrieved onboard, as we did not know the full extent of the repair. At this point we had the option to patch or machine if required.
On inspection, the patch repair was intact and showed no signs of damage or deterioration. The original coating had failed from the "starboard" side of the patch right around the rod circumference to the forward face of the rod.
The decision was made to blast the coating away from the total circumference of the rod, with a height of approximately 20". The theory being that if this was indeed a bad section of coating due to the positioning of a steady rest during the original coating procedure, as described by Hydralift, then we could remove and replace the whole area which would prevent future failures.
The blasting was completed and an application of bond coat was applied. Finally forty ceramic rods were sprayed onto the blasted area. The photograph below shows the spraying process and the blasted rod with additional bond coating.
The total time for blasting this area was approximately 12 hours. The coating time for forty rods was approximately 4 hours. On future work, this spraying time should be extended to 6 hours to allow an additional twenty rods to be applied.
On completion of the coating process, the machinists move in and set up their equipment. They set up the frame with precision to ensure the rotation/machining will be uniform all around the rod. From the photographs below, you will see that the equipment clamps around the rod and rotates around the circumference. The machinists perform runs of approximately 6 inches in width and measure the diameter with a micrometer, until it is equal to that of the original rod diameter. The grinding machine is then lowered in the frame for the next run. In total, four passes were made in approximately 14 Hrs.
Below are some photographs of the machining process.
Machine Set up
Machine Set up
Machining Process
For the first attempt, the final result was good. After machining, there was some hand finishing required, due to some low spots following the coating process, which prompted the decision to apply more rods in future. However, the machine finish was excellent and much more precise than the hand finishing that we had done in the past.
Below is a photograph of the finished repair.
Following the machine finishing of the repair, the rod seal was removed and inspected. The photograph below shows two sections of the original seal cut off the rod. The damaged areas can be clearly seen.
The whole seal was replaced with a new "split" type for ease of installation.
If this repair proves to be reliable, it is felt that it may be prudent to repeat this process for the remaining five rods during upcoming rig moves, whether they are damaged or not. It may be possible to perform this work on two rods per rig move, depending on the amount of time available.
NATIONAL THERMOSPRAY, INC.
5120 Oak Ave.
Pasadena, Texas 77503
Contact Ken Norris
OFFICE: 281-373-0609 or 281-991-1133
Cell 713-898-6844
Fax: 281-991-9911