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What is Corrosion under insulation (CUI)? Corrosion Under Insulation (known by its acronym in English, CUI) is a phenomenon that normally affects pipes and pressure equipment made of carbon steel, as a result of the entry or condensation of water under the thermal insulation. Within this category of corrosion can also be included the corrosion generated –for the same cause– under the lagging (CUF, corrosion under fireproofing) of pipes and pressure equipment.

The inspection of storage tanks in accordance with the American API standards are vital to avoid not only catastrophic failures but also problems related to their mechanical integrity affected mainly by corrosion on floors, walls, and ceilings. In this article we want to show very quickly and graphically the different elements / techniques / equipment for carrying out inspections according to API-653 and with IN OUT SERVICE condition of the tank (in this link you can find information on equipment for conducting operational inspections for storage tanks)

The inspection of storage tanks in accordance with the American API standards are vital to avoid not only catastrophic failures but also problems related to their mechanical integrity affected mainly by corrosion on floors, walls, and ceilings. In this article we want to show very quickly and graphically the different elements / techniques / equipment for carrying out inspections according to API-653 and with IN SERVICE condition of the tank (in this link you can find information on equipment for conducting operational inspections for storage tanks)

The probability of failure in a storage tank can be low but the consequences can be catastrophic. A leaking storage tank can not only cause serious environmental problems, affect human and animal life around it, but can also have a major impact on the profitability of the operation in the form of product loss, unscheduled downtime and prolonged repairs to rectify the damage, as well as environmental remediation and non-compliance with legislative clauses. That is why the inspection of them and especially the floors play an important factor. Full surface coverage with NDT inspection was often prohibited due to inappropriate methods that are time-consuming and therefore too expensive. This created the demand for so-called detection tools with which suspicious areas can be detected very quickly. In recent years, several of these methods have been introduced to the market. This article will discuss two methods that can be applied to carbon steel components.

In the past article we talked about the techniques to inspect volumetrics defect, now… Let us start with traditional methods and the most recent techniques to detect surface and sub-surface discontinuities:

When talking about this topic, we must consider at least 3 important aspects: i) Welding, which is already an extensive topic, but here we can define very briefly that it is a process that leads to the union of two or more materials together, in such a way that they remain as a single piece. For the purposes of this article, we are talking about metallic materials. There are many welding processes (At SOLDOZA we are experts in everything related to welding, see references), in other articles we will describe the welding processes in detail. ii) The defects present in the weld, as in the previous point, we will detail these defects in other related articles (see references). And the… iii) Non-Destructive Testing including: …techniques both surface detection and volumetric inspection. Each technique has its own advantages and limitations, but in most cases, they can be complementary and combined to provide operators with the most comprehensive data. Thanks to the continued advances in NDT technology enables improved detection of defects and sizing.

Nickel belongs to group VIII of the Transition elements together with Iron and Cobalt. It has the atomic number 28 and an atomic mass of 58,6934, representing a composite of 5 stable isotopes. In solid state, it has FCC crystallographic structure with a lattice constant of 0,35167nm at 20ºC. Nickel doesn’t show allotropic transformations in the entire ranges of temperatures up to the melting point. Its electronic configuration is Ar 3d8 4s2. Pure nickel has 0,2% offset yield strength of 59MPa and Ultimate Tension test of 317MPa with an elongation of 30%. Due the high solubility of many other elements, there are an important number of commercial alloys, which improves its mechanical properties by solid solution or secondary phase’s precipitation.

The 9%Ni steels could be welded using filler metals with similar chemical composition if the appropriate heat-treatment is applied to match the mechanical properties of the base metal. Filler metals having 12% nickel have also been developed, showing good toughness but low ductility. Welds made with this consumable have shown good results in the laboratory test, but have not been accepted for the construction of large vessels.

Natural gas is transported by pipelines at high pressure, LPG, where the maximum rentable length is around dozens of thousands of kilometers or at low temperature and ambient pressure by LNG sea carriers, where natural gas could be transported for longer distances than LPG technology. At both sides of LNG production chain, the product should be temporally in storage; after liquefaction, while is waiting to be charged on LNG carriers, and at the receiver side, while it is waiting to be processed in the regasification plant. This temporal storage of Natural Gas is made in liquid state at a temperature below -165ºC in LNG tanks, which are designed like huge multi-layer thermos, with a few insulator layers placed between different structural parts of the tank.