Completion & workover operations are complex: temporary equipment is deployed to access to a pressurised oil or gas well, changing the well integrity and barrier philosophy. On subsea wells offshore, the completion & workover riser (CWOR) string is normally deployed by a drilling rig, providing a direct conduit from the well to the rig floor.
The CWOR also acts as a backbone for service lines (annulus access, umbilicals), which are strapped to the riser joints and connect to control packages above the rig floor. A the rig moves and heaves, a wear casing is strapped to the outside of the joint running through the rig floor (making it a cased wear joint) protecting the service lines from damage.
Risk management starts long before operations, as risks are identified and mitigated through HAZOP studies, which extensively cover the “what-if” scenarios for every operation.
While the wear casing serves an important purpose, it significantly degrades the reliability of the rig’s diverter function, which would protect rig floor personnel in the event of CWOR or subsea test tree (SSTT) failure – both of which could result in gas release in the marine riser annulus. This is because the seams, gates and voids in the wear casing allow gas to flow through at high rates.
SRP’s sealing wear casing effectively mitigates this risk, by: sealing on the main riser pipe, sealing on each umbilical, service line and annulus line, and providing a smooth outer surface for the diverter to achieve a seal.
The casing construction is steel and there are no loose fixings or fittings that can drop in the well bore. We can supply the casings as individual modules, or a complete cased wear joint.
In conjunction with our sister company – InterMoor – we developed the proven Rocksteady subsea mooring connector into an acoustically operated quick disconnect connector: Rocksteady QD, marketed as InterMoor’s Inter-M Release.
A quick disconnect connector is loaded with energy that releases the connector at the press of a button, this functionality can save days of rig time, and even protect assets from extreme weather events. However, the connectors are part of the mooring system that keep drilling rigs in position over a well, so managing the risk of accidental release while providing the required availability presents a significant engineering challenge.
SRP managed this risk through FMECA based design methodology and a rigorous testing program that included control software unit and user testing, and extensive factory acceptance testing.
By issuing type approval, DNV has certified that the integrity of the Rocksteady QD acoustic release meets or exceeds the system reliability requirements set out in DNV-OS-E301 for Position Mooring.
We are pleased to announce that Rocksteady – our subsea mooring connector – has been awarded United States Patent No. 10,144,488.
This patent award validates the world class innovation here at SRP. Rocksteady also has ABS and DNV type approval, and we are always improving and optimising with our product development program … these are all hallmarks of a quality product.
Johnny Shield, Managing Director, SRP
The connector features automatic latching and can be preloaded to withstand bending and torsion loads, improve fatigue life and optimise subsea installation. Rocksteady is now far smaller and easier to install than any other subsea quick connector.
Since the original qualification and fatigue testing in 2012, SRP has developed multiple derivative Rocksteady products, including hydraulic lifting tools, remote control high load release, and ROV-free connectors loaded with sensors.
We’ve all accidentally dropped our phones and watched them shatter in apparent slow motion while we vainly grasp at the air or, worse, kick out a foot, only to propel the (now smashed) phone across the room.
But why do our smartphones shatter, when your old Nokia 3210 would bounce around happily on concrete with barely a scratch?
Part of the reason is that there is now a big screen that can shatter – the screen in a 3210 was only about 20% of the size of the phone, modern smartphones are nearly all screen.
Another reason is that modern phones are slabs of glass and aluminium, made to feel heavy so they feel expensive compared to the cheap/flimsy/plastic versions that creak when you hold them to your ear. So is it all that extra weight that’s causing the issue? Well yes, that is a part of it. The Nokia 8210 is only about 1/3 of the weight of a plus phone, which means only 1/3 of the kinetic energy that must be dissipated when it hits the floor. Surprisingly though, the difference isn’t normally that stark – this modern droppable from Huawei weighs the same as a 3210!
So what gives?
Part of the expensive feeling of a heavy phone isn’t actually the weight, it’s the stiffness: the phone doesn’t flex, so it feels more substantial. It also feels more substantial to the ground and does not flex elastically (i.e. bounce back) as readily when struck or dropped, compared to a thin plastic shell. If the structure cannot flex, the energy is then dissipated locally, typically as cracks in your screen or dents in the aluminium chassis.
The challenge of efficiently absorbing and distributing impact energy is studied across a huge range of fields, subjects such as:
car crashes (cars have crumple zones, and air bags, which are crumple zones for your face)
phone case makers (probably, though that might just be fashion)
Below is a short clip from a study of different designs of bumper for our subsea mooring connector. You can see how the different structures absorb energy very differently, one flexes like bamboo in the wind, the other results in a dented dome. So, which is better?
Lighter and more flexible is often a desirable outcome for the simple reasons of less material, less cost. However, structural integrity and interfaces with adjacent objects can often be the deciding factor. In the above case, where the bumper is just a bumper, the overriding design factor is the interfacing geometry during and after impact. We can tolerate a dent in the dome and it is covered by a flexible urethane coating, so this is acceptable. The first case shown has large lateral deflections, these will impact the working parts of the connector so must be avoided.
I’m off to buy a phone case.
Got a comment or correction? Here’s the post on linkedin.
InterMoor, the world leader in mooring services, has obtained the exclusive rights to our quick disconnect variant of Rocksteady – Rocksteady QD – for traditional offshore mooring. The connector will be used as part of their game-changing mooring technology called Inter-M Release, which allows operators to safely drop moorings away from the rig and saves days in prelay moves and weather avoidance.
The QD connector retains all the functionality of a subsea mooring connector as well, so can be used with InterMoor’s SEPLA and other pre-installed anchor technologies.
Read more on InterMoor’s press release on their website. If you would like to know more about using the Inter-M Release system, you can drop us a line, we’re more than happy to put you in contact with the right people.
Our engineers are power users of Sharepoint’s PowerApps functionality, so we have put it to good use – creating a size calculator to enable our sales team and partners to rapidly respond to requests for quotation.
Rocksteady holds design approval certificates from both DNV and ABS for our scaling method all the way up to 3,000t; and each bespoke size is subject to FEA performance verification, proof and break load testing.
FEA has always been one of our core analysis tools, though it has become more important as our products are developed with advanced strain based design techniques.
Why do we do this? It is driven by the our markets, for example: mooring applications define manufacturing test loads above yield (see video below!), and HPHT (20,000psi) codes refer to ASME Div III design methods. Strain based design also confers reliability and efficiency advantages: localised regions of stress above yield can be assessed and checked against strain data from testing.
Our engineers operate ANSYS FEA software, routinely modelling subsea and riser equipment with 2D & 3D linear (elastic) analysis and non-linear (plastic) analysis. Some of the services we offer include:
Simplified axi-symmetric stress analysis for concept level designs
Detailed 3D stress analysis for complex components and structures
Analysis of parts and assemblies with complex contacts
Modal and frequency response analyses
Stress linearisation and assessment against API, ISO, DNV and NORSOK codes
Below you can see a video of a stud-link chain analysis that we completed with our sister company InterMoor. We developed a detailed wear model of the chain interfaces to predict wear rates with bending loads applied, following deformation of the chain to the proof loaded condition.