Industry collaboration delivers world’s first proven DNV-GL Type Approved means of repair for corrosion-resistant alloy clad or lined subsea pipelines
Read the full article in UT3 Magazine, Issue 4, August 2020.
Authored by James Rowley, Business Development Director, Connector Subsea Solutions
The oil and gas industry is renowned for its ability to overcome technical challenges, particularly those that arise when operating in deep water, high pressure environments.
For every new challenge that is faced, it is addressed and solved through brilliant engineering and innovative technology, and another potential solution is added to the engineer’s ever-expanding toolbox.
This means that today, almost any issue can be addressed using a combination of engineering and technological solutions that have been developed over the years, enabling successful exploration and production even in the most complex fields, in the most challenging environments.
As the industry has evolved, so too have the challenges, but some have been with us since the 1970s; for example, how to effectively produce oil with either high sulphur or carbon dioxide (CO2) content with its corrosive qualities. The same challenge exists for the production of gas with high hydrogen sulphide (H2S) content.
And this is a challenge that prevails today. According to the International Energy Agency, it is estimated that 70% of the world’s remaining oil reserves consist of crude oil with these qualities that require the use of high quality, corrosion-resistant materials in order for it to be produced safely and effectively.
Initially, duplex pipelines were the solution, however these come at a significant cost and in many applications are superseded by clad and lined pipelines which were first put into service in the late 1970s. These pipelines consist of a carbon steel parent pipe that provide the necessary structural strength, clad or lined with a high value corrosion-resistant alloy (CRA).
An effective solution for the challenge at hand, but with one major drawback; if seawater enters the pipeline the damage to the CRA can be critical and irreversible. In the case of a future need to intervene with the pipeline for planned modification or bypass operations the cost could be extremely prohibitive, but what about the risk of an emergency repair situation?
Regardless of the best engineering and planning, every pipeline in the world is at risk of failure; corrosion, erosion, fatigue, dropped objects, dragged anchors, impact damage, even sabotage represents a notable threat is some geographic locations.
Although the probability of damage or failure occurring is relatively low, the associated cost in terms of risk to health and safety, environmental damage, lost production, and potential resulting operational and reputational issues is significantly high. Therefore, a means to contain, mitigate or perform an emergency repair is a critical element in the engineer’s toolbox of solutions.
However, historically there was no proven means of repair for subsea pipelines that are clad or lined with CRA. This meant that any damage to a pipeline would leave the operator with two options; (1) the high-risk and expensive strategy of deploying unproven technology, or (2) isolating and replacing the entire pipeline system and accepting the significant associated lost production that this operation would incur.
In-situ welding options have been concept-proven, however, the lack of a field deployable solution coupled with the poor suitability for emergency repair requirements make this an unattractive and unworkable solution for subsea repairs in both shallow and deep water.
The use of mechanical connectors in the repair of standard pipelines including carbon steel, duplex and stainless is commonplace, field-proven and with expansive and detailed DNV-GL Type approved solutions readily available. However, these existing products do not suit CRA clad or lined application due to the CRA pipe being made up of a composite with the clad core layer. If cut to allow installation of a conventional mechanical connector, the aggressive media being transported can bypass the clad layer and penetrate the base metal with detrimental effect.
Identifying a clear gap in the market and the need to find an effective and proven means of repair, in 2010 a Joint Industry Project (JIP) between Chevron, another major oil and gas operator and MORGRIP®, a DNV-GL Type approved connector system since the late 1980s got underway.
MORGRIP proposed that by making modifications to its standard mechanical connector, the same benefits of performance, reliability and long-term integrity could be achieved when using the connector on CRA clad or lined pipe.
All MORGRIP mechanical connector products use the same radial sealing system, a metal-graphite-metal sandwich arrangement, which is compressed onto the pipe’s outer diameter during connector activation. The standard seal assembly consists of two metal anti-extrusion rings either side of a graphite ring. The metal rings provide the primary seal due to their intimate contact with the inner diameter of the coupling and the outer diameter of the pipe. The graphite filler material provides resilience, longevity and caters for any imperfections on the pipe surface.
The seal has exceptionally high performance, a long life and is particularly tolerant of surface imperfections which are inevitable with many pipeline applications.
During the JIP, using extensive analysis and testing, MORGRIP engineers developed a reliable, repeatable and predictable method of successfully end sealing onto the inner lining of a clad or lined CRA pipe by mechanical means. The technology is fully protected by a standard patent with a 20-year term.
In 2019, after five years of successfully collaborating on deep water pipeline repairs, the MORGRIP products and business was acquired by Connector Subsea Solutions, specialists in providing repair and tie-in solutions for pipelines, risers and subsea distribution systems. The acquisition coincided with the completion of the JIP under the guidance of DNV-GL.
Existing MORGRIP technology facilitates the replacement of damaged sections of pipeline by gripping and sealing onto the outside of the pipe either side of the cut-out repair position. Although acceptable for conventional pipelines, clad or lined CRA pipelines require a means of sealing at the CRA layer which runs through the core, ensuring that the line media does not bypass and reach the parent pipe material leading to critical failure.
To prevent this scenario, the sealing onto the inner lining has been achieved through the development of an end seal module which is incorporated within a standard MORGRIP connector. The module is designed to use existing knowledge from the work on the radial seal and fill a defined volume by pressurizing a ring of graphite on the cut end of the pipe.
As with the main graphite seals, the end graphite seal requires anti-extrusion features to prevent an increase in seal volume, reducing the seal pressure. These two features exist within the end seal module and are able to consistently and reliably ensure end seal action on the full range of pipe tolerance including mean, maximum, minimum, ovality, skew, eccentric and even weld beads.
The technology qualification was carried out in accordance with DNV-GL RP A203 and conducted in three phases: Proof of Concept, Prototyping and Production. The testing requirements were reviewed, approved, executed and concluded under the vigilant watch of the JIP partners and DNV-GL. The testing primarily focused on:
- The retention of the graphite seal mass through the anti-extrusion features
- The controlled pressurization and flow of the graphite seal
- The activation sequences for diver and remote (deep water) applications
Upon successfully completing the Proof of Concept and Prototyping, a 16” 300 barg subsea connector was built to production specification based on DNV-GL OS-F101/RP-F113 and NACE MR0175/ISO15156.
The scope was based on an existing offshore requirement and included the additional stringent requirements of the operators’ specification. Upon completion of additional testing on the production unit, the MORGRIP Clad and Lined Pipe (CLiP) Connector was added to the MORGRIP product range’s DNV-GL Type Approval. This approval, for carbon steel, stainless steel and duplex pipelines already covered ½” to 42” sizes with pressures up to ANSI Class #2500 and temperatures from -40 degC to +250 degC.
As the specification from the JIP was driven by exact operator requirements, the DNV-GL Type Approval for the MORGRIP CLiP Connector has been limited to 10” to 26”, up to 364 barg, up to 149 degC, but remains applicable to onshore, topside, subsea and deep-water application.
James Rowley, Business Development Director, Connector Subsea Solutions explains; “MORGRIP is a great product with a strong track record and we were confident that some modifications would allow us to develop the world’s first proven and only DNV-GL Type Approved means of repair for subsea pipelines that are clad or lined with a corrosion-resistant alloy.
“On the face of it, these modifications and extension of these parameters may seem to be quite a straightforward process as the end seal module is designed to fit within the existing MORGRIP technology. However, to repeatedly and reliably accommodate all pipeline tolerances has taken a lot of work by our team of engineers and we are very proud of what has been achieved by doing what we do best – developing bespoke engineering solutions to overcome challenges.
“We are extremely grateful to the JIP partners for their guidance, patience and investment in Connector Subsea Solutions. We remain 100% committed to supporting their future requirements and look forward to seeing the MORGRIP CLiP Connector being deployed subsea as soon as possible.”
More than 3200 MORGRIP connectors have been supplied to the oil and gas industry over the last 30 years, and Connector Subsea Solutions and MORGRIP is the worldwide supplier of all but one field-deployed remote connector repair in the last 23 years.