Presentation about HIC Damage

April 2009

What is the phenomenon HIC, fully named Hydrogen Induced Cracking, in steel?

Free atomar hydrogen, chemical symbol 'H', can diffund from the product inside the vessel/column/heat exchanger and can pass through the steel to the outside. On its way to the outside it can connect to several components which were used to manufacturing the steel, and it can cause damage when it binds itself to another hydrogen atom, thus forming hydrogen gas, H2. In the gas and oil industry H2S is present very often. It also contains free atomar hydrogen, H. Nevertheless there is a wrong opinion saying that the higher the percentage of H2S, the quicker HIC damage will occur.

I will show you 2 examples:1) A cap of a storage drum.

This drum was used at a Dutch natural gas plant, producing sweet gas. The percentage of H2S was lower than 2 ppm, but still blisters were formed. Beside the blister no indications are found by UT-testing. See the images below.

2) Damage in an LPG accumulator.The H2S percentage was between 10 and 50 ppm. In this case we could follow the growth of the damage, and in report 11 and 12 you will find all the information from the start of the damage until the drum was rejected. The reports also include information about HIC resistant steel.

Another point is that people often think that in a clean end product no H2S is present anymore. Absolutely clean is nearly impossible. That is why we show you in report 13 that HIC damage can be found in gas bullets/spheres with products ready for sale.

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In the past HIC damage was only visible when it occurred as blisters. For following the growth the size of the blisters was measured and recorded. This method is still in use in the USA (see attached pages). All other indications in the material detected by UT-measurements were classified as dirt in the material, caused by the manufacturing of the steel. It is nowadays for many people, who aren't familiar with HIC damage, still the same answer: the item is 30-40 years old, so there will be dirt in the steel.

In 1965 I started my profession as UT-operator. In that time most of the present refineries where built. We tested many plates which were to be used to build vessels, towers etc. Even in those years we tested with a high sensitivity. I cannot remember that we detected many indications.

Of course HIC damage starts with help of the small inclusions inside the material. In the beginning the HIC damage is too small to detect by UT-testing. But when this process continues, the defects will grow, and from a size of about 0,1 mm we can detect it and follow the growth by testing according to our procedure.

We are asked many times if we can see the difference between laminar defects caused by HIC damage and defects caused by manufacturing the plate.

Laminar defects caused by manufacturing are lying in one line in the steel, and are flat. With angle probe testing no indications will be found.

Laminar defects caused bij HIC are cracks running through the structure of the steel and they are not flat. With angle probe testing you get indications from the small steps.

Of course it is possible that laminar defects from manufacturing start to grow due to HIC damage, but the new laminations will have small steps.

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When HIC damage starts, we are able to follow the growth. Even when laminar defects have a size of 3,0 mm or 5,0 mm we are able to say that when HIC damage continues till stepwise cracking, the stepwise cracks run in length: or in circumferential direction, or in longitudinal direction of the item. It is rather unknown, but it is a fact that the length of HIC laminations runs in the length direction of a plate.

When stepwise cracks are present, the length of the cracks will also run in the length direction of the plate.

In many big items, where the shell parts are made of 1 plate, the cracks (when they are present) will run in a circumferential direction. These cracks have no influence on the strength of an item. In smaller items it is possible that the plate will be rolled in a direction, perpendicular to the length of the plate. When in this case stepwise cracks start, the direction of the length of the crack will be longitudinal. In this case a risk based calculation will be needed. The situation in caps can be different because we cannot see how the plates are pressed to form the caps.

In seamless pipe it is possible that HIC damage can start. There are 2 possibilities. When the material is not clean, it can start in the whole range of the wall thickness. You can read about it in report 5A/6A. When seamless pipe is made from clean material HIC damage can grow inside the material but only in the first millimeters from the inside, and spread as single points in the pipe (see attachment report 6A). The length of the stepwise cracks runs always in longitudinal direction.

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Stepwise cracks

Rolling directionwhen the platewasmanufactured

A question we often get is if we know where HIC-damage can start. There are many factors involved. Of course it depends on the quality of the steel and the kind of product that is inside the vessel. Over the last 22 years of testing for HIC damage we have gathered some rules. We are looking for wet HIC damage (temperature below 80C).

a) When we have to test airfin coolers, we start with the outlet header (the coldest part). Also in heat exchangers we start looking at the coldest spot, around the outlet nozzle.

b) In some items there is a dead end present. No clear flow of the medium is present there, and dirt will have a change to fall down, causing a condition where HIC damage can start. An example is shown in report 5A, about a seamless pipe, with a lot of dirt in the dead end. Dead ends can also be found in in horizontal vessels, for example between the outlet and the cap.

c) From towers we check always the lower part (liquid), below the inlet, opposite the inlet and the top part.

d) At first-time spot-check testing we always check the liquid phase as well as the gas phase. It can happen that HIC damage only exists in the liquid phase, or only in the gas phase.

But once again, these are not stated facts, it can always start at different positions.

We have a procedure for investigation for HIC damage. It was developed together with Shell Research. With this procedure we can give you the information you need. We talk clear about the size of a defect, if it is in laminar or in thickness direction. With our classification system, ranging from 0 till 10, the client knows what kind of damage the item has. When stepwise cracking is present, the client will be informed whether the length of the cracks runs in circumferential or longitudinal direction. For following the growth of the defects we use a computerized report, where you can see if the damage is growing. When a client has an item with serious damage, and he wants to make a risk based calculation, we can offer the defects of this damaged area on scale 1:1.

Since 1996 we are testing for HIC damage, and since then we have learned a lot. We know that HIC damage can start, but it can also stop again. We have seen items which, after being 30 years in H 2S service still no or no serious damage. A little change in the service can cause the start of HIC damage, see report 13 about an LPG storage tank.

We try to find out if HIC damage is present. We test a fixed area 100 % in regular intervals, and do spot-check testing as much as possible of the remaining part. When HIC damage is growing fast, we advise to check the item completely. We have also clients who say: if an item has no indications, class 0 according to our procedure, after 10 years of spot-check testing, the item has to be tested 100 % again.

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In the years 1992-1995 I published books about many different items with HIC damage and other sorts of damage. When you have read this text, you know now a lot about HIC damage. After 23 years it is still interesting to look at and search for HIC damage. We have no real information about the new HIC resistant steel yet. We will wait another 10 years and after this period we will find HIC damage there as well.

I hope you liked my presentation. I am sure I do not know everything about HIC damage. When you have any questions, please let me know and I will try to give an answer.

Kind regards,

J.C. Verkade

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