Alfredo JONES

Advances in E&P technology, new deep-water discoveries combined with the  global increase in demand for oil & gas products has led to much of   the world’s aging offshore  infrastructure including  platforms & pipelines to still be in operation.

This article deals with some newly developed survey methods & innovative & cost effective Cathodic Protection solutions that are helping to make it easier for life extensions of aging oil & gas infrastructure, and reducing the consequences of catastrophic structure integrity failures due to corrosion.

Introduction
Advances in technology, has enabled oil and gas companies to be able to produce more oil & gas and for longer periods, hence the need for life extension solutions for older offshore oil & gas producing facilities, which in many cases have reached or are reaching the end of their design life, but are still in operation.

Initially, a lot of these facilities where designed with a life span of 25-30 years, once they reach this age, offshore structures are at the highest risk of catastrophic external corrosion failure, as their Cathodic Protection systems which were designed with the same life span as the structure they were meant to protect have now reached the end of their useful life or are depleted, so they are not protecting the structure anymore and need to be replaced.

The result of structures without adequate corrosion protection is that the  integrity of the facility could be compromised, which could lead to structural failures or leaks due to corrosion, the  consequences could be costly accidents, loss of life, loss of production, pollution to the environment etc

Even with the above mentioned consequences of not maintaining the structural integrity of offshore oil & gas structures, there are still a lot of facilities out there operating without adequate corrosion protection. Reasons range from poor maintenance cultures, like don’t fix it till it’s broken to the high costs involved in replacing (retrofitting) depleted anodes on offshore facilities.

Corrosion Protection of offshore oil & gas facilities
Offshore oil & gas infrastructure is protected from seawater corrosion through Cathodic Protection which works by either a galvanic (sometimes called sacrificial) anode, or an impressed current anode and power supply, into an immersed corrosion circuit.

They work by supplying sufficient low voltage direct current (DC) flows from the anode to overcome the natural DC current that flows from the offshore steel facility into the seawater during the corrosion process, this causes the corrosion to cease.

Corrosion protection of offshore structures traditionally involve the use of sacrificial anodes attached to new structures during fabrication or just before been put in the sea. This is easy to do and is cost effective as the corrosion protection solution is either welded or bolted on before the structure is put in the sea.

The conventional  approach to a CP retrofit, when the CP system has reached the end of its design life, is to replace anodes on a one for one basis, this approach is completely un-necessary as it is very costly, complicated, dangerous for divers, in some deepwater cases impossible i.e. divers cannot reach below certain depth to attach  replacement  anodes.

What to do?
There are three basic strategies that offshore oil & gas facility owners should adopt when considering a CP retrofit:
1.CP Survey of the facility
2.Retrofit a Cathodic Protection system on the structure
3.After installation, survey &  carryout routine monitoring

CP Surveys
Regulatory requirements state that routine CP surveys should be carried out on offshore oil & gas facilities. Having said this, a lot of operators don’t routinely survey their facilities, or when it is done in the case of pipelines, the survey is usually of little value because the method used is not adequate.

The types of survey performed may be broadly categorized as surface deployed potential (drop cell) survey and diver or ROV assisted potential survey. The drop cell survey involves dropping a portable reference electrode in even depth increments through the structure and the data is displayed on a topside meter and hand recorded.

Subsea surveys are carried out by physically contacting the structure or pipeline at intervals with reference electrodes through divers or an ROV. It can also be done through connecting permanent reference electrodes to the structure & taking CP readings of them. The survey will let the CP engineer know the condition of the structure and make informed decisions regarding CP retrofit designs.

New and innovative cathodic protection retrofitting Solutions for offshore structures
The main reason for carrying out a CP retrofit on an aging offshore oil & gas structure is that the original CP system would have depleted, and the integrity of the structure which has to be maintained is compromised, while the structure is still in operation.

A few companies specialising in providing corrosion protection solutions like Deepwater Corrosion Services inc, in the US and UK, recognised the high costs, logistics and health, safety and environment concerns involved, in replacing depleted cathodic Protection systems (anodes) on offshore structures and have developed a series of non weld retrofit options that include  galvanic (sacrificial) anodes and impressed current cathodic protection systems, that cut down on cost, reduce installation time and that can be installed at depths that cannot be reached by divers.

Innovative ways of connecting CP retrofit solutions to structures

RetroClamp
RetroClamp provides fast reliable electro-mechanical tieback for subsea cathodic protection systems. Originally designed for pipeline CP retrofit applications, the RetroClamp is now widely used in a variety of subsea retrofit projects including connecting retrofit CP systems to platforms, FPSOs & wellheads, they  can either be installed by diver or ROV.

Innovative CP retrofit Solutions for Pipelines

SmartMat
The Smart Mat is a galvanic (sacrificial) anode system that combines the proven technology of a segmented concrete stabilization mattress with an integrated cathodic protection system. This is an excellent solution for the retrofit of an aging or damaged pipeline.

Placing the mat directly over the pipeline provides up to 30 years CP for up to 2 miles of pipeline in each direction. This is easy to install, by just dropping over the pipeline with a crane, and the tieback to the pipeline can be made via ROV or diver with the RetroClamp system.

Innovative CP Retrofit solutions for FPSOs, Platforms & Welheads
A way to reduce the cost of doing a CP retrofit on a structure is to reduce the number of anodes that need to be installed to get adequate CP to protect the structure. As mentioned, traditionally you would have had to replace every depleted anode, which is costly, time consuming & dangerous.

With the new innovative ways, cost is reduced, because installation time is reduced, there is no need for welding and the number of required anodes is drastically reduced to provide CP protection. Two patented systems on the market are the Retrobouy which is an impressed current system and the RetroPod which is a Galvanic (sacrificial) anode system.

RetroBuoy
The RetroBuoy is an efficient and environmentally responsible CP retrofit system with high capacity impressed current cathodic protection designed to be retrofitted to existing structures. The RetroBuoy can provide up to 400Amps of CP, protecting approximately 80,000Sq ft of underwater steel and this makes it a better and viable option than the conventional method which requires many anodes.

It’s typical for large and smaller offshore platform complexes. The RetroBuoy has a single float version which is called the RetroBuoy Jr. and its provides reliable CP when depth and current conditions allow for all varieties of dock and jetty structures.

RetroPod
The RetroPod is an aluminum anode system arranged in stable, self contained ‘’pod”, which is ideal for replacing depleted anodes on mature assets. The RetroPod is extremely cost effective for replacing or supplementing the CP on aging offshore structures that sit in between 85ft and 300ft of seawater.

The installation of the RetroPod with an ROV makes it suitable for any depth limit. The RetroPod is less expensive and its installation time is less than a quarter of the time it would take to install the equivalent amount of CP anodes using the traditional method which also gives the structure an additional weight with the clamp-on anodes.

After installation, survey & routine monitoring
Cathodic protection systems should be monitored for performance, from topsides with the drop cell method, from subsea typically by divers or ROV measurements of the level of protection, at commissioning stage and routinely thereafter. Galvanic anode systems require monitoring but no maintenance if properly designed.

By Alfredo Jones, Managing Director of Alduco Energy company.