Monday, June 15, 2020

Geoff Connors Presents Buoyancy Control for Very Large Pipelines

This presentation was presented to the International Pipe Line & Offshore Contractors Association (IPLOCA) in May 2020.


Good morning, this is Geoff Connors for PipeSak pipeline products in Canada, this is my presentation for the IPLOCA Spring 2020 session webinar due to the COVID 19 situation.

The topic of my presentation is buoyancy control for very large pipelines, a case study. Hope you enjoy it.

As we all know oil and natural gas piplines frequently require some form of buoyancy control. Negative buoyancy, whether crossing bodies of water, swamps or more commonly just groundwater. Of course, the larger the pipeline diameter the greater the need.

This past year my company, PipeSak, was asked to design and manufacture a weighting system within extremely tight tolerances and constraints to control the buoyancy of three 84 inch diameter water pipelines. The project proved not only challenging but groundbreaking in many respects. I’d like to present PipeSak’s small but critical component to the success of this important project.

As a little background we at PipeSak pride ourselves in supplying innovation to the pipeline construction industry, helping to make pipelines a little safer through the use of modern technology.

In the late 1990s PipeSak delivered the world’s first geotextile fabric pipeline weight that was suitable for the rigours of pipeline construction.

15 years later we brought an innovative new way to support and protect pipelines in areas of rock, the PipelPillo. Most recently we refined an existing product to protect the pipelines’ coating in areas of light rock, the PipeJacket.

In the coming months we will be introducing two products to further protect pipelines. PipeDefender, which will allow trench backfill in areas with large rocks, and the PipeArch, which is designed to protect buried pipelines from above ground load.

As we all know water has always played a large part throughout the history of the Netherlands. The Dutch certainly deserve a reputation as the world’s experts on how to handle and control water. After an uncommonly dry summer in 2018 the Dutch water supply company Evides received government approval to improve the accessibility of water in the southern half of the Netherlands. The project involved a new high capacity intake pumping station at the Bergsche Maas, and the pipelines to supply it. Evides contracted a Belgian company DENYS along with the large dredging company Van Oord to design and build a system of three 84 inch diameter pielines to stretch from the Bergsche Maas to the Buchbasch reservoirs.

Early in 2019 DENYS approached PipeSak to help with the design of the buoyancy control system and to supply PipeSaks and the DENYS crew could fill right on site.

The PipeSak buoyancy control system is not common in Europe. I believe we were considered in large part due to the involvement with IPLOCA, and the contacts we made there. For this I thank Juan for tracking me down to join a few years back.

I’m sure other methods to control pipeline buoyancy were considered by DENYS, including concrete coated pipe. I suspect PipeSak was selected mainly due to the extreme environmental significance of the area where importing gravel and concrete was likely frowned upon or not allowed.

Not even being allowed to use local fill as ballast gave PipeSaks a huge advantage.

As mentioned earlier, DENYS, was to build three sperate pipelines each with a diameter of 84”, and a wall thickness of 22.2 millimeters. The pipelines connected a large reservoir to the north, and a water source to the south at Bergsche Maas. The pipelines construction setup to the north and all three pipelines were pulled in unison southerly.

The pipe itself was heavy, weighing in at 1153 kilograms per meter. The upward buoyant force acting on it was a whopping 3572 kilograms per meter. A lot of weight will be needed to sink this pipe. The top picture is inside the welding shack when they were welding the 84 inch pipe, and the bottom picture shows an earlier version of the PipeSak just to give you a look at the scale of this pipe and the PipeSak.

EVIDES had a few tough requests for PipeSak. Number one, each PipeSak can be no longer than 1.13 meters when filled. Number two, to ensure there is room for adjacent pipeline the leg width could be not exceed more than 760 millimetres. Number three, the height of each PipeSak could not exceed 2.54 meters, or about 200 millimeters off the trench floor once its installed. And most importantly, number four, once installed, each PipeSak had to weigh at least 440 kilograms using only the silty sand excavated from the trench.

Through the years PipeSak has supplied buoyancy control for many water pipelines, though our typical projects are oil and gas. From four and a half inch to 40 inch OD pipelines, 114 mm to 1212 mm in diameter. Our largest PipeSak to date was for a 56 inch pipeline project in natural gas. The PipeSaks were actually filled with an iron ore to achieve a dry weight over 17,000 pounds or 7700 kilograms. PipeSaks are typically filled with gravel in gravel pits local to the pipeline as shown here with clean sand or gravel being used as ballast. As filling is completed the PipeSaks are stockpiled right on site while we’re inside the gravel pit and retrieved by contractor as needed and then trucked to the site, installed on the pipeline and then backfilled. Pretty straightforward.

Using our typical design criteria DENYS would not be  able to place PipeSaks close enough to achieve the negative buoyancy they wanted. The dimensional restrictions demanded for this project the excavated material was just not dense enough. In my view we needed to import proper gravel, in addition the plan was to drag all three pipelines into position in unison. The friction of fully weighted pipelines on the trench floor would be immense, if not impossible to overcome. DENYS design a method to overcome both concerns by adding heavy marine chains they could achieve the negative buoyance incorporating a small amount of flotation near the bottom of the trench, reducing any bottom friction and coating damage.

Once installed the marine chains, which were 70 kilograms, attached to each PipeSak, and 1.3 ton marine chain draped over every 15th PipeSak. It had enough additional negative buoyancy to drag the pipelines down to the bottom of the trench. As they approached the trench floor the longer chains were designed to partially fold up, to reduce the negative buoyancy to a point where the pipeline buoyancy was just plus of neutral, allowing all three to float submerged just off the trench floor.

I don’t know, this may be a common offshore practice, but for an onshore guy, I found the solution ingenious. But DENYS ingenuity didn’t stop there. With PipeSak and the chain design each PipeSak butt up against the next there was little margin for error. It was critical for DENYS to ensure the weight for each PipeSak was right on design. Since the PipeSaks are so tall, a standard PipeSak filling frame would not be efficient or safe. Plus, the use of somewhat sticky material would be tough to get into the PipeSak. So based on PipeSak’s base frame, DENYS engineers and welders evolved it into a tall solid frame with two vibrating plates on the bottom to help get the fill down to the bottom of each PipeSak.

For consistency and to help get the moist ballast out of the excavator’s bucket, a high capacity bucket and excavator was also design and built for the project specialty with two controllable gates and a another vibrator.

Following filling every PipeSak was numbered and weighed, both dry and under water. The loaders would help relocate each PipeSak to the stockpile were equipped with load cells on each fork. Not only did they know the total weight of the PipeSak, but they knew the weight of each side of the PipeSak just to ensure it doesn’t tip over on the pipe.

For the underwater weight each PipeSak was submerged into water tanks for 20 minutes to ensure the void spaces was reduced. Just prior to removing from the water tanks the submerge weight of every PipeSak was carefully recorded. Once removed from the saddling tanks the PipeSaks were immediately stockpiled and 70 kilogram chains were attached with specially designs straps sewn into each PipeSak.

Every 15th PipeSak required an additional 13 meters of marine chain draped over each pipeline. Here’s a shot of those chains and they’re huge. The PipeSaks were eventually relocated to the water’s edge adjacent to the crane for installation since PipeSaks were to be placed on the pipeline by barge and crane access to release the individual PipeSaks was restricted. A specially designed lifting devices was made to spread open the PipeSak legs to install over this wide pipe, allow the crane operator the ability release the PipeSak with the flip of a switch. All three pipelines were pulled in by a series of winches on a barge approximately 500 meters away. I believe DENYS screws were welded and installed one to two joints per day on all three pipelines.

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