Compression limit state of HVAC submarine cables
- Authors: Reda, Ahmed , Forbes, Gareth , Al-Mahmoud, Faisal , Howard, Ian , McKee, Kristoffer , Sultan, Ibrahim
- Date: 2016
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 56, no. (2016), p. 12-34
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- Description: An industry accepted standard does not currently exist for determination of compression limits in a subsea cable. This has resulted in most manufacturers specifying that subsea cables are not permitted to be axially loaded in compression.Additionally industry guidance does not exist regarding the consequences of inducing compression forces within subsea cables and the resulting effect on cable integrity. Industry recommended practice and guidance also does not have any information regarding experimental test arrangements to determine allowable compression levels within a subsea cable. This lack of modelling/testing guidance along with manufacturer recommendations of zero compressive loads within subsea cables results in overly conservative and restrictive design parameters for subsea cable installation and use.Due to the complex interaction within a subsea cable structure, such as contact interaction and friction between cable strands, theoretical modelling has been unable to provide reliable stress predictions and therefore an experimental testing regime is required if compression limits within the cable are to be appropriately determined. This paper describes combined axial and bending test arrangements that can be used as a guideline for determination of allowable compression limits for subsea cables. © 2016 Elsevier Ltd.
Design and installation of subsea cable, pipeline and umbilical crossing interfaces
- Authors: Reda, Ahmed , Howard, Ian , Forbes, Gareth , Sultan, Ibrahim , McKee, Kristoffer
- Date: 2017
- Type: Text , Journal article
- Relation: Engineering Failure Analysis Vol. 81, no. (2017), p. 193-203
- Full Text: false
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- Description: Deterioration of subsea cable, pipeline and umbilical crossings often occur due to relative movement between the crossing members. Any crossing design should aim to achieve a sound, fit for purpose solution that will be maintenance free over the crossing life. Due to the increased density of subsea fields, crossing instances need to be increasingly accommodated. Current subsea design codes are not explicit in the criteria for subsea crossings, beyond recommending pipeline separation distances. The work within this paper describes two case studies in the novel use of articulated padding applied to the crossing member, using the crossed pipeline as a support and then using the articulated padding resting on traditional grout-bag supports. The results highlight the ability of the articulated padding to provide the required separation on subsea crossings without the need for extra support design. It is also shown that the articulated padding can be used on grout-bag shoulder supports to allow full subsea crossing separation for crossing lays that will undergo large environmental loading conditions, and hence relative motion. The results presented also provide a basis for the development of future industry standards incorporating articulated padding designs. © 2017 Elsevier Ltd
Guidelines for safe cable crossing over a pipeline
- Authors: Reda, Ahmed , Rawlinson, Andrew , Sultan, Ibrahim , Elgazzar, Mohammed , Howard, Ian
- Date: 2020
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 102, no. (2020), p.
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- Description: High voltage submarine cables are increasingly being installed in existing and new offshore oil and gas fields for power supply and control purposes. These power cables are both large and with a high submerged weight, which poses a challenge when designing a safe, maintenance free (economical), and fit-for-purpose crossing over a pipeline. Damage to subsea pipeline crossings caused by deterioration of a crossing support, field joint materials and cover components is well known in the industry, particularly with old pipelines. Crossing cables over an existing pipeline should be avoided whenever economical and practical. However, it is inevitable in some situations to use the existing pipeline (unburied) as the crossing support to a new cable/umbilical. In these situations, crossing the cable/umbilical over the existing pipeline may be a cost-effective and worthy consideration. However, there are no explicit guidelines or criteria in the industry concerning the acceptable practice of design and construction of crossings. The only clear recommendation is relating to pipeline separation distances. This paper documents a recent case study of damage of a field joint coating at a crossing of an existing pipeline by a 132 kV subsea cable of 191 mm outside diameter. Investigation of the damage on site revealed that it was caused by lateral movement of the cable under the influence of hydrodynamic forces. Further to investigation and assessment of the damage of the case study presented here, the paper proposes some guidelines for the safe design and construction of cable crossing. Another objective of this paper is to invite further evaluation of the proposed guidelines so that appropriate crossing design requirements can be further developed and standardised. © 2020 Elsevier Ltd
Failure analysis of articulated paddings at crossing interface between crossing cable and crossed pipeline
- Authors: Reda, Ahmed , Elgazzar, Mohamed , Sultan, Ibrahim , Shahin, Mohamed , McKee, Kristoffer
- Date: 2021
- Type: Text , Journal article
- Relation: Applied Ocean Research Vol. 115, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: While subsea crossings are undesirable for many reasons, they are unavoidable due to the sheer density of subsea assets. The use of articulated paddings is a cost-effective and practical method to achieve the required vertical separation between the crossing and the crossed pipelines or cables, though, not without limitations. In this paper, the failure of articulated padding at several points along a subsea cable in operation was investigated. The articulated padding has experienced partial fractures at numerous crossing locations and in some places has fallen off the cable completely. A complete failure mode analysis was conducted where several possible modes of failure were considered in detail. In-place finite element (FE) analyses of the articulated padding components and the corresponding environment were also performed. The FE modelling concluded that the original design loads were significantly lower than the expected worst-case load scenarios. To replicate the failure mode, two abrasion tests were also conducted and the results of which were studied. It was concluded that the predominant failure mode (partial fracture to the articulated padding discs) was likely a combination of the increased dynamic loads, excessive lateral movement causing unexpected levels of fretting, unbalanced free span causing unexpected stress concentration factors and reduction in material mechanical properties. All above factors have contributed to the root cause of the system failure and instigated the predominant mode of failure “partial fracture”. © 2021