What is Sour Service for pipeline system?

Any process fluid that contains hydrogen sulphide is defined as Sour Service.

As per MR0175, it is a process atmosphere that contains H₂S, which may lead to cracking in the material.

Sour Service is also known as wet H₂S service in a refinery. You must be thinking, what is special about it?

Well! H₂S is a highly toxic gas present in the Oil and Gas environment. A small exposure to it may have a serious effect on human health. It is colorless and flammable. It has a very unpleasant smell.

If it leaks into the atmosphere and when combined with water, it can create acid rain.

In refineries, it is found in crude oil areas,  hydro treater areas, LPG areas, and wastewater facilities.

It is heavier than air, so it will sit in the lower area and wait for its prey.

Not only this, its presence leads to corrosion in metals such as  Sulphide stress cracking, Hydrogen induced cracking, stepwise cracking, and Stress-oriented hydrogen induced cracking.

This type of material cracking leads to catastrophic equipment failure in plants.

So this H₂S is dangerous for humans, the environment, and property. That is why special attention is required when it comes to sour service.

What Materials are Used in Sour Services?

Regular Carbon steel, Alloy steel, and stainless steel are used in sour service. Here, I have listed a few for your reference.

But there are a few additional requirements that these material needs to meet before installing.

Here are the additional requirements for carbon and low alloy steel.

1. Steel shall be manufactured by Basic Oxygen Process or Electric arc furnace.
2. Steel to be Killed & fine grained.
3. Materials shall be in Normalized Condition.
4. Nickel % limited to < 1%
5. Carbon content< 0 .23%
6. Carbon Equivalent < 0.43%
7. Hardness < 22 HRC
8. Sulphur content< 0.01%

Similarly, for stainless steel material, there are specific requirements of alloying elements and heat treatment with limited max hardness.

Now let’s see What are additional tests required for these materials?

What are the Additional Tests Required for Sour Service Materials?

1. HIC – Hydrogen Induced Cracking
2. SSC – Sulphide stress cracking,
3. SOHIC – Stress oriented hydrogen induced cracking

Also, after welding, PWHT is required for all carbon and low alloy steel material used in sour service.

Requirements for testing and acceptance criteria are given in NACE MR0175. So, go through it if you want to know in more detail.

Also, note that NACE MR0175 is the same as ISO 15156.