As regional oil producing companies and countries march ahead with their plans of ramping up oil production in this current battle to defend market share, oil and gas equipment, drilling platforms, tools and manufacturing units in use are being subjected to more wear and tear than ever. Rigs and machinery – particularly in the high corrosion sectors such as offshore and sour gas – are rusting rapidly, thereby burdening companies with increased expenditure on maintenance and repair.
In this low oil price era, when energy players are striving to do ‘more with less’, corrosion control thus assumes paramount importance. Although a natural phenomenon, corrosion, if left unchecked, has the potential to not just render equipment useless but also damage entire operations.
Regional oil and gas companies have not been known to spend much on the proverbial ‘stitch in time’, as a result of which local oil and gas equipment corrode by an estimated 4 to 5% annually, according to a senior industry expert.
“Normally you get 4-5% degradation annually, depending on the equipment and its usage. That’s what you get when you build a pipeline and don’t look at it – within 10-15 years it is out. So you have to put the protection and make the investment to recover some of it or eventually you will have to replace it,” Mohammad A. Al-Sultan, manager of Saudi Aramco’s Mechanical Services Shops Department, told Oil & Gas Middle East.
Are some sectors more corrosion-prone?
Corrosion in the oil and gas industry can occur on both the internal and external surfaces of production and processing equipment. Aqueous corrosion occurs in the presence of water. Internally, the main corrosion threats are due to carbon dioxide (CO2), hydrogen sulphide (H2S), microbially induced corrosion (MIC), and under-deposit corrosion.
Safety Critical Elements (SCE), or equipment that handles potentially hazardous fluids such as hydrocarbon liquids and gases, are fabricated from carbon steels, making them prone to rusting. CO2 corrosion is caused by the creation of carbonic acid in solution, which is aggressive to carbon steels. As the flow rate increases the rate of corrosion can increase, causing Flow Influenced CO2 corrosion (FICC).
In addition to corrosion, SCE’s can suffer from stress assisted environmental cracking. For the internal surface of carbon steels, this is typically in the form of Sulphide Stress Corrosion Cracking (SSCC), Hydrogen Induced Cracking (HIC) and Hydrogen Blistering caused by the presence of Hydrogen Sulphide (H2S), or sour gas.
“Different parts of oil and gas processing units will be more susceptible to corrosion depending on the fluid properties and metallurgies used in certain parts of the asset. Produced fluid that contains high sulphur content or sour gas is more corrosive and more care should be taken to ensure the pipe wall is not corroded too quickly,” Jake Davies, marketing director, Permasense, told this magazine.
When H2S is present, the corrosion rate can increase further, and can be calculated using mathematical models. However, sour gas producing units are not generally prone to corrosion and H2S in fact can also be ‘beneficial’ in reducing general weight-loss corrosion, as one expert points out.
“Some operators even deliberately introduce H2S into pipelines to lower corrosion rates. But, some material such as high strength steel, can fail in different ways by cracking when H2S is present. There are well known international standards (ISO 15156) that provide guidance on the safe selection of materials for sour gas conditions,” Dr. Liane Smith, founder and managing director of Wood Group Intetech, says.
“Elemental sulphur production can be exceedingly aggressive to carbon steel and the most effective protection is to keep the sulphur in solution by adding solvent, so that it does not deposit as a solid on the surface of the steel. Sulphur is a catalyst to a specific set of reactions that can cause localised pitting. Corrosion rates from sulphur deposits can be over 10 millimetres per year.
“In many cases the worst corrosion can be in the less high profile systems. Operators worldwide are plagued by corrosion in their water injection systems because of the difficulty in maintaining excellent oxygen removal from water. Excursions in conditions to higher oxygen levels quickly result in high rates of corrosion attack,” she added.
According to Smith, non-flowing ‘dead-legs’ can be another problem area for operators because the low flow conditions encourage proliferation of microbial species. “There is a vast amount of hydrocarbon nutrients in oil and gas systems and temperatures are generally pleasantly warm, encouraging microbial species to colonise the surface with a microbiological biofilm. Under this slimy film the species metabolise hydrogen sulphide into various other sulphur species like sulphate ions – the same way animals metabolise oxygen to carbon dioxide to get energy – and those sulphur species then cause localised corrosion of the steel,” she said.
Effective corrosion control
The global cost of corrosion in the oil and gas industry was estimated by the US National Association of Corrosion Engineers (NACE) to be over $5bn. Without online monitoring of corrosion in their operational assets, it is almost impossible to know whether operators are investing enough in corrosion control.
A reduction in capital expenditure favours the use of cheaper metallurgies in the building and maintenance of oil and gas assets. However, this must then be adequately monitored and may result in increased operational spend in corrosion inhibitor chemicals.
There is consensus among industry players, however, that the GCC oil and gas industry is quite aware of the menace of corrosion eating into both its budget and operations.
“I would say that over the years, corrosion management in the regional oil and gas industry, and at Aramco specifically, has been good,” Sultan told this magazine on the sidelines of the Manufacturing Conference & Exhibition for Oil & Gas (MAF 2016) in April in Dubai.
He elaborated on an interested practice at Aramco: “I think we have gone a long way in protecting our equipment and scrapping our pipelines. Aramco has designed and implemented a quality inspection programme that monitor all aspects of degradation, corrosion and erosion. We have Aramco-designed specific corrosion programmes. We have 17-steps that we need to comply with and each operating facility needs to comply with. It (inspection) happens every year. Then there are findings (reports) also. I think in the last 7 years we have made a leap forward in corrosion control through this 17-step programme.”
Dr. Hussain Al Fadhli, secretary general of the Saudi Council of Engineers, revealed to this magazine during the recently held that Aramco spends about SAR 1bn ($266.58mn) each year on corrosion control.
Industry professionals suggest a number of methods for efficient corrosion control, with the choice of technique being used based upon its ability to work effectively and also the cost of applying the technique. Andrew Duncan, lead consultant at Intertek Production & Integrity Assurance, outlines a number of proven methods to contain rusting of equipment.
“Corrosion inhibitor chemicals are used to manage internal corrosion in carbon steel pipelines, while biocides can be used to control sulphate reducing bacteria. Scale inhibitor chemicals are also used to control scaling precipitates in pipelines, while wax inhibitors are used to control wax deposition in pipelines. Metallurgical solutions may be used to control SSCC and HIC by controlling the hardness of the steel and by using steel with low levels of inclusions,” he says.
He further suggests: “Corrosion resistant alloys may be used to manage very high corrosion threats, however, these materials also have their own corrosion risks. Cathodic protection can be used to protect the external surfaces of buried or submerged pipelines and structures and also of the internal surfaces of vessels. Coatings can be used to protect the external surfaces of buried or submerged pipelines and structures and also of the internal surfaces of vessels. Coatings are also used on above ground or surface steel work which is exposed to marine environment corrosion. Design may be used to minimise corrosion, for example by using swept bends to reduce erosion, and by avoiding ‘dead legs’ in process piping.”
Along with corrosion management techniques it is essential to deploy corrosion monitoring techniques which measure the corrosivity of the fluids, and non-destructive testing (NDT) techniques which measure the wall thickness of the SCE, analysts recommend. In 2015, the GDP of the UAE was estimated to be $406bn, hence the theoretical cost of corrosion at 3.1% was a mammoth $12.18bn. For Abu Dhabi alone, with an estimated GDP of $206bn, the theoretical cost of corrosion at 3.1% amounts to a whopping $6.38bn.
“The cost of corrosion reports estimate that 25% of the amount spent could be saved by application of corrosion management techniques, equating to a potential saving of $3bn and $1.6bn for the UAE and Abu Dhabi respectively,” Duncan said.
“It is important to understand that corrosion is first and foremost a safety risk which has to be managed. Once the safety risks are managed the economic risks associated with uncontrolled corrosion will fall into place,” he said.
