[MODULE 2 PART 2] API 571 (3rd ED, Mar 2020) - API 570 STUDY GUIDE - AMINE STRESS CORROSION CRACKING

API 570 STUDY GUIDE 
AMINE STRESS CORROSION CRACKING
API 571 (3rd ED, Mar 2020)

Amine Stress Corrosion cracking or Amine SCC or Amine Cracking

Amine SCC is related to tensile stress, type of amine and temperature

Amine SCC causes CRACKS in Carbon Steels and Low-alloy steels. 

1. Description of Damage

Amine SCC occurs by the combined action of tensile stress and an aqueous alkanolamine solution. 

Note that pure alkanolamine does not cause Amine cracking so an aqueous alkanolamnie presence is needed for cracking to occur.

Amine Cracking is a form of Alkaline Stress Corrosion Cracking (ASCC). 

This is to be noted as cracking can occur because of the environments of caustic solutions, chloride solutions etc.

Amine cracking is most often found at or adjacent to non-postweld-heat-treated (non-PWHT'd) carbon steel welds or in highly cold worked parts.

There are other types of SCC that can occur due to the presence of amine.

2. Affected Materials

Carbon Steels and Low-alloy steels (LAS)

Note that Stainless Steel (SS) is not mentioned in this.

3. Critical Factors

The critical factors are 

    Level of tensile stress

Increasing the tensile stress increases the likelihood and severity of cracking. 

What are the conditions for increase of tensile stress? Residual stress from welding and cold working.

How to overcome this? By an effective stress relieving heat treatment.

Temperature

Increasing temperature increases two things

1)the likelihood of cracking

2)severity of cracking.

In MEA service cracking has been reported at ambient  temperatures also.

Type of Amine

There can be a confusion while understanding the type of amine causing the cracking.

In general amine cracking is most often associated with lean amine services, where a solution of amine and water is used.

More likely this type of cracking can occur in MEA and DEA Services.

If steam out is done in an equipment or piping which carry amine, then a solution of amine and water is created and that equipment/piping will have a likelihood to crack similarly short term amine carry over equipment and piping are also prone to this type of cracking

Please note the following

1) Pure alkanolamine does not cause cracking

An equipment carrying alkanolamine is subjected to steam out. Will it create a chance for Amine SCC? 

Yes. Anywhere, if there a lean amine (Amine and Water) solution is created then there is a likelihood of ASCC.

2) In rich amine services in H2s removal systems, the H2s helps to form a Iron sulfide (FeS) film on steel surfaces that helps impede amine SCC.

3) Cracking in rich amine services is most often associated with wet H2s.

The interesting part is amine concentration does not appear to have a significant effect on the propensity for cracking.

4. Affected Units or Equipment

All non-PWHT'd carbon steel piping and equipment in amine service, including contactors, absorber, strippers, filters, regenerators, heat exchangers as well as equipment subject to amine carry over, or where there is a chance to create a lean amine solution are subject to cracking.

Will continue in the next blog...

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