Line Stopping Used to Change Leaking Valve with Zero Interruption to Production in Nigeria

Summary of Project

Wellube team successfully completed a 10” and 12” double position line stop operation for one of our client’s in Nigeria without any interruption to the production.

Client Requirement

The client approached Wellube to change-out the leaking valves, with spools, without stopping the existing live line and to continue the production uninterrupted.

Challenges

• Careful manual excavation had to be performed to ensure safety of the pipeline
• As the project location was near the seashore, tide water was constantly seeping into the excavated location
• The concrete coating on the spool needed to be removed prior to the welding on the pipe
• Specific safety regulations needed to be followed for confined space welding
• As the line medium was Liquified Natural Gas (LNG), preheating had to be performed to avoid cracks and other issues due to welding

Unique Solution delivered

The solution Wellube provided was performed at several stages beginning from preparation of the site to completion of the project inclusive of tests to assess the integrity of the pipelines.

First Stage of the Project:

The project began with the clearing of the dense bushes on site, followed by the manual excavation process to avoid damaging the pipeline due to normal use of heavy equipment, such as tractors and mechanized diggers. Dewatering pumps were utilized throughout the project due to the job site’s proximity to the beach

Second Stage:

Following the site clearing and manual excavation, the pit walls of the confined space were securely shored up. The concrete coating on the spool was removed using a high-pressure water jetting machine, after which the weldolets and split tees were welded on the 10” and 12” pipelines.

The pipelines were preheated to avoid cracks due to welding as the line medium in both the pipelines was cold liquified natural gas. This was followed by non-destructive tests to ensure that the pipelines were in good condition.

Final Stage:

The hot tap machine was mounted on the 10” spool and pressure tested with nitrogen to check for any leaks on the fittings before the cutting operation could begin. The same process was also carried out on the 12” pipeline. Pressure test was also carried out for all the 4” gas bag insertion valves as well as on the 2” vent and equalization points on both the 10” and 12” pipelines.

After completion of the hot tapping process, the temporary sandwich valves were closed, the hot tap equipment dismantled, and the linestop and bypass housing and spool installed, and leak tested using nitrogen. Line stop heads were introduced into the pipeline for isolation and diversion of gas flow through the bypass spool.

For the secondary isolation, gas bags were inserted through the 4” valves and inflated with nitrogen, thereby, preparing the redundant spool to be cut in order to remove the faulty leaking valves and install the new pipe spools. The redundant valve sections were cut using our pneumatic driven cold cutting machine and the entire process of cutting was completed in about 3 hours.

Nitrogen was used for continuous purging during the inline welding of the replacement pipe spools, which were tack welded in place, after NDT tests were carried out, followed by full encirclement welding.After completion of all welding activities, radiography testing was carried out to ensure no weld defects were present. The pipelines were equalised, and normal flow was established. The cut coupons were welded on to the 4” completion plugs, and the respective plugs were inserted into the 4” line stop & 2” vent fittings.

All service equipment and temporary bypass lines were removed, the pipelines backfilled, and the site was returned to its original state.

Despite the challenges of the site location and difficult work conditions, the entire project was completed in a professional and safe manner by Wellube’s team, with no production downtime.

Benefits Delivered

• Avoided shutdown of the pipeline
• Customized solution with zero loss of production
• Project completed within the timeframe
• Fully HSEQ compliant with zero incidents