Hydrascope Flooded Member Detection

HydraScope Flooded Member Detection is designed to indicate whether through-thickness cracking has occurred to a structure, resulting in member flooding, without the need for the member to be cleaned down to bare metal. This allows detailed crack inspection to be carried out on a limited number of high-risk members, saving both time and cost.

The use of radioactive sources for the inspection for flooded members on offshore steel structures is a well-proven technique. FoundOcean have operated with radioactive sources offshore for more than 25 years and have successfully utilised logging techniques for various monitoring applications.

The HydraScope Flooded Member Detection system was developed from this extensive experience to address the specific needs of repair and maintenance programs in conjunction with subsea inspection requirements. The majority of FoundOcean’s offshore personnel are trained and competent in the safe use of radioactive sources.

Equipment and Operation

Foundocean uses a small radioactive source mounted in a source housing detector pod. Computer and FMD software logs all relevant data and produce reports. A radioactive source and robust detector unit are mounted on opposite forks of a variable yoke positioned across the diameter of the member under inspection. The equipment can be configured to operate at any angle from horizontal to vertical to suit measurements on horizontal, diagonal or vertical members.

The ROV-mounted FMD system operates on the principle that a collimated beam of radiation is transmitted through the member and received by the detector at the other side. The strength of the received beam is compared with computer predictions for a dry or flooded member. These predictions are derived from calibration measurements performed in a specially-constructed test assembly in FoundOcean’s laboratory near Edinburgh.The system is mounted on the front of any ROV type and requires a screened twisted pair and a 24 volt power supply subsea within the ROV umbilical.

Performance

The design of the system permits inspection of members with diameters from 150mm to 2000 mm and wall thickness of up to 60mm to be tested. The system in normal mode can determine whether a member is dry or flooded with 100% accuracy. Reliability of the results allows checks to be carried out quickly. Foundocean has carried out FMD jobs in a variety of different locations, please see track records page for further information.