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Pipeline Integrity Management

Chemical Cleaning and Internal Coating of 22" Subsea Bulk Loading Pipelines

Project Overview

The Primary Client, Ital Petroli operate a Fuel Storage and distribution Depot in Civitavecchia, Port of Rome.

This facility is supplied with refined fuel products including heavy fuel oil and Jet fuel via a 16 km pipeline system consisting of twin 22” subsea pipelines running from an offshore loading tower located approximately 1.5 km offshore. 

As a result of a Magnetic Flux Leakage (MFL) survey by Rosen, it was discovered at the time to have suffered what was thought to be up to 85% wall thickness loss due to what was established as Sulphate Reducing Bacteria Attack.  Picture 1 below shows typical SRB pitting on one of the spools that was removed from the loading tower.

Before starting any operations, it was discovered that the internal surface of the pipeline at the valve stations was uniformly covered with what was initially thought to be some form of localised internal coating (Picture 2). This was subsequently revealed by Camera Survey to be far more extensive, i.e. the entire pipeline was affected.

As there had never been any internal coating applied during the 9 year life of the pipeline, Consub recommended a Chemical Analysis of this material and it was discovered to be a very Sulphur Rich, Calcium Carbonate deposit.  This was a very fortunate discovery as acidizing the pipeline as per the procedures would have resulted in vast quantities of H2s being produced into the atmosphere.

As a result, Consub developed and managed an extensive mechanical cleaning program to remove this potentially deadly deposit and some 7 to 10 tonnes was removed. Picture 3 gives an indication of the amounts of deposit removed during each mechanical cleaning run. 

 

 

 

 

 

 

At this stage, the client (ItalPetroli) was informed that the accuracy of the MFL survey would have been affected by this deposit as Rosen were also unaware of its presence and as a result, wall loss could have been higher than the 85% maximum reported.

However, it was agreed that acidisation could now take place with minimum risk to personnel and the environment.

Several pig runs were executed using a 17% concentration of inhibited Hydrochloric Acid to remove corrosion products from the pipeline prior to internal coating.

Unfortunately, during the final stages of the pre-coating works, leaks were discovered in the land section of one of the pipelines and at a subsea flange at the riser base at the tower. Subsequent investigations revealed that the wall loss at the onshore leak location was greater than 85% and that the flange leak was due to massive external corrosion caused by galvanic action and external bacteria attack (see Pictures 4, 5 & 6).

These leaks were repaired but after recent dewatering and a subsequent air test, more leaks were found both on and offshore.

The situation is now under evaluation as to how to proceed to rectify a major integrity issue and Consub are providing assistance and expertise during this investigation.

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Scope of Services

Consub acted as a Consultant to PNS NL in the preparation of procedures for the Chemical Cleaning and Internal Coating of the said Pipelines.

Consub also provided Project Management services on site in Civitavecchia during the works execution phase and are acting as a Consultant in planning the best course of action to take to rectify the situation.