Free Span Mitigation Methods

The DnV-RP-F105 (Free Span Pipelines, 2006) and DnV’s FatFree Program can be used to check for the maximum allowable free span length. If the actual free span length exceeds the maximum allowable free span length, the free span should be corrected using one of the mitigation methods below (also see Figure 12.3):
• Alteration of seabed (cut-off high seabed spots by plough or trencher)
• Concrete mattress or sand-cement bags
• Mechanical support
• Strakes or fairings

Figure 12.3 Examples of Free Span Mitigation Methods

(a) Mechanical support

(b) Strakes

(c) Fairings

Source:

Lee, Jaeyoung. 2007. Introduction to Offshore Pipelines and Risers.