Ship Collision Study
A Ship Collision Study is required to assess the hazards arising from external impacts during the normal operating mode and maintenance, leading to possible loss of containment and asset damage.
The overall risk posed to a given facility from ship to platform collisions is dependent on two (2) factors as follows:
- Likelihood of a vessel colliding with the facilities
- The impact energy (as a function of vessel mass and speed)
There are two (2) primary concerns in assessing the impact consequences to the platform. The first major concern is the potential for a critical platform structure to be hit (such as a platform leg) leading to its failure and subsequent loss. The loss of the platform structure may be gradual if the platform load is redistributed amongst the remaining structural elements leading to their subsequent failure.
The second major concern is an impact onto the risers, which may cause their immediate failure and the subsequent combined effect of a massive hydrocarbon release and platform structural damage. The situation may be further exacerbated by the potential ignition of the hydrocarbon release by sparks created by the ship’s movement against the platform.
Evaluation of ship collisions risk involved the following steps:
- Identification of marine traffic, which could impact on the facility
- Determination of collision frequencies from historical data
- Estimation of the probability of marine traffic impacting critical platform structures
- Determination of the consequences of ship collisions on critical structures by estimating the energy transferred from a collision event.
Ship traffic data is used as the basis for the ship collision study. The following ship traffic data is typically required for a ship collision study:
- Merchant vessels passing the installation (per year)
- Supply boats to nearby platforms (per year)
- Supply boats to distant installations (per year)
- Shuttle tanker to the platform (per year)
- Fishing vessel density (per km²)
- Supply boat arrivals to the platform (per year)
- Effective boat loading / unloading time at the platform (hours / year)
Therefore, two (2) distinct groups of marine vessel traffic are identified to have the potential to collide with the wellhead or gas gathering platform:
- Passing Vessel in Contact with WHP / CGP – Passing vessels (External Traffic) are vessels not related to the facility, including merchant vessels, fishing vessels and offshore traffic unrelated to the WHP / CGP
- Infield Vessel in Contact with WHP / CGP – Infield vessels (Field-related traffic) are offshore traffic serving the platform, e.g. supply vessels, standby vessels etc.