This page contains a Flash digital edition of a book.
TECHNICAL PAPER


15


Pitfalls with steel anchorage within your refractory lining. Part 3


Jan Theron


I started my career as a chemical engineer within SASOL. The career change to refractories happened as a result of my association with a former colleague, Louise Boshoff, who always said there is never a dull moment working with refractories. Starting at minute by minute quality control sixteen years ago, my career path soon expanded very fast covering inspections, failure analysis, installation improvements, lining design, maintenance strategies which resulted into a move from South Africa to the UK six years ago.


Steel anchorage is used to secure a refractory lining to the steel shell of the vessel, but because they are hidden within the refractory material, their condition is not evident during inspections and repairs. Assuming the anchor is still holding the refractory concrete in place could be fatal to personnel working inside the unit.


In part 1 a few common failures of refractory linings containing steel parts have been discussed. Part 2 gave some insight to the very interesting aspect of sigma-formation in certain grades of stainless steels and in this section the corrosion mechanism of chorine and sulphur, will be discussed and the effect it has on sensitised anchors.


Introduction


Steel anchors are very often used for securing cast or gunned monolithic refractory material to roof sections of high temperature units. This allows for a simpler design and faster installation compared to brick linings.


Most of the gunned and cast refractory materials used in the industry shrink during dry-out. After the first heat-up, followed by subsequent cool downs, the refractory panels rely heavily on the anchors to keep them in position. The condition of the anchors is, therefore, a critical factor ensuring a safe working environment for people working inside these units during inspections or repairs.


In the past “clean” fuels have mostly been used, but with the change to alternative fuels, the scenario has changed. It automatically led to the development and selection of more corrosive resistant refractory materials. However, at first the steel anchoring systems have been neglected to some extent. This has changed over the years as more problematic shutdowns were seen which were associated with anchor failure, some even resulting in fatalities, when large cast blocks dislocate from the outer structure.


Therefore, more focus has been given on the reactions of steel with aggressive media such as sulphur, chorine and alkali environments at high temperature. This also led to alternative manufacturing methods for steel anchors which reduce stress points in the anchors. Some of these findings will be discussed in this paper.


Chlorine Attack


Chlorine is found in many alternative fuels which attacks the refractory lining, but more so the steel anchoring associated with castable linings.


NOVEMBER 2014 ISSUE


Figure 2: Formation of scale around the steel anchor causes cracking of the refractory castable around it


WWW.IRENG.ORG Figure 1: Remains of a 310SS anchor exposed to chlorine after only 4 months Jan Theron


The effect of severe anchor corrosion can be seen in Figure 1 where 310 SS grade anchors were used in the presence of chorine and sodium within the burning zone of a thermal oxidiser operating at temperatures around 1450°C. The amount of scale formed caused severe cracking of the refractory lining (See Figure 2). Furthermore, severe corrosion took place at the interface between insulation and hot face lining, completely destroying the anchorage to the steel shell.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36