When there are so many important issues in running a fertilizer plant, then how high up in importance is the amount of corrosion in a facility? To put it into perspective, NACE International carried out a survey in 1978 and 2016, estimating that the cost of corrosion for the US was US$276 million in 1978 and, by 2016, had reached a staggering US$1.1 trillion, excluding indirect costs, such as loss of income during shutdown periods. Today, approximately 5 metric t of steel is degenerated every second worldwide, and 40% of all produced steel is used to replace corroded steel.
These figures make for an interesting introduction, but what do they mean for the fertilizer business?
To look at this, we need to understand the differences between operations of the different plants and units within these plants. For example, an ammonia factory takes a long time to shut down and start up again. This means that planning is of the utmost importance. An actual fertilizer plant or a blending plant, on the other hand, are relatively easy to shut down and start up again and, by the nature of the product, these stoppages are frequent. So, maintenance of the plant can be easily carried out. ‘Easily’ is probably the wrong word, but this will be discussed later.
The topic of corrosion control is by necessity broad. This article will focus on corrosion under insulation (CUI), which is relevant to all types of facility.
CUI is a very complex subject. Prior to the 1970s, there was little discussion and very little understanding around the subject. Insulation had started to be used more extensively due to the oil crisis at that time in an attempt to reduce the energy required to operate the plants. Subsequently, the advantage of a balanced temperature system for the process and of course safety meant the use of insulation has become more and more extensive. During the 1970s and 1980s, it was considered unnecessary to think about corrosion under this insulation as it was for hot service. Therefore, either no coatings, or only very basic coatings, were used. Vapour barriers were introduced, and the efficiency of these can be discussed at length, but one thing we know is that water will manage to get into the insulated systems.
This is an article written for World Fertilizer's November/December 2017 issue and abridged for the website. Subscribers can read the full issue by signing in. Non-subscribers can access a preview of the issue here.