Making sure your sonar cable matches exact specifications is crucial, especially in the naval defense sector. How does proper Subsea Cable Testing work?
To be able to prove to your customer that all requirements of their (sonar) cable have been met, testing and validation are indispensable. How do you do this as efficiently as possible?
You can only do this by knowing when analyzing data will suffice and for which components or metrics extensive subsea cable testing is required.
We will discuss various verification methods and the importance of testing and validating thoroughly on this page.
There are many different applications imaginable for a subsea cable. Testing and Validating are the constant factors in all of these applications. After all, the client and you as an engineer need to be sure the requirements are being met. This is particularly important in the defense market.
Proper verification enables you to check and describe a subsea cable’s mechanical performance and the applications/situations it can be used in safely.
A lot of verification can be done by analysis (calculations, computer modeling, or comparing similar products). This is usually a lot cheaper than extensive subsea cable testing. However, analysis can’t tell us everything we need to know. The complex geometry and construction makes subsea cable testing vital for verifying a cable’s real-life behavior.
It is virtually impossible to rely solely on computer-based analysis. This can even be dangerous. The verification process has to be as complete as possible, to not take any chances.
Besides testing and analysis, there are three other verification methods we can use, bringing the total to five:
The Design Compliance Matrix forms the foundation of the project. It determines for each requirement how we are going to verify that it is met. For this purpose, a choice is made between the five possibilities above. Sometimes multiple verification types are used to verify a requirement. For example, analysis may be used in the design phase, followed by testing during the development phase.
Inspection is the checking of visible specifications that are passed on from the customer. For example, does the cable contain the specified amount of drain wires?
Demonstration is used to demonstrate operational specifications. In this way, we can immediately see whether these specifications are realistic and can be met in-field.
The CoC (Certificate of Conformity) ] is provided by our suppliers, who have already done testing/analysis on their own components. The CoC can then be used as evidence for verification, nullifying the need for additional tests.
Analysis and testing are explained more in-depth below.
While conducting tests can never be completely excluded, there are a number of factors within subsea cable testing that can be verified through analysis. Calculations, modeling and simulations can be sufficient, without expensive tests. Three examples are strength, environment, and lifespan.
Strength is perhaps the most important factor to analyze. Of course, the strength of a cable is verified later by testing, but before the cable is built, materials and the cable design are already analyzed for strength. This prevents modifications at a later stage.
The environment in which a cable will eventually be used can also be analyzed. After all, there is data from areas like oceans on temperature, chemical resistance, salinity and depth. For example, you can easily analyze how temperature- or chemical-resistant your cable should be.
The third factor, lifespan, mainly relates to fatigue. For example, can the cable be towed behind a ship for 5,000 hours? This can be analyzed with data on waves or other movements, cycles and variations in tension and comparing these operational conditions with the fatigue life of the strength member by using the proper fatigue model.
Analyzing is a cheap(er) way to verify certain requirements, but as an engineer, you cannot neglect subsea cable testing. Relying on analysis alone can even be dangerous. That is why qualification testing and a proper FAT are of vital importance. Examples of subsea cable testing are deployment/retrieval, electrical/optical data measurements and the Elongation VS Load test.
One of the main requirements of a subsea cable is how often it can be launched and retrieved. Every cable is custom-made, and it is vital that the cable can handle being launched and retrieved the right amount of times. The bend over sheath fatigue test is therefore a standard part of the qualification tests.
Verifying electrical and optical properties is a fixed part of the FAT. Standardly performing electrical and optical measurements is important, as this can reveal defects in components. For example, the insulation resistance between two components may be too low. Missing such defects can jeopardize the project.
The third important test is the Elongation VS Load test. It is crucial that the cable does not stretch beyond 0.6% when loaded to prevent permanent deformation. This must be verified by subsea cable testing.
Whitepaper Mechanical Tests
Before subsea cable testing and analysis are even on the table, a thoroughly specified cable design must be created. After all, you cannot test or analyze a cable if there are no requirements and specifications to check.
Read more about cable construction and how the geometry of a cable is determined here:Read more
How do you stay as cost and time-efficient as possible in your cable design process?
Our R&D Manager shared important insights on cable construction and a couple of proven verification methods in our webinar. Download the recording here and rewatch the most interesting parts any time you like: