B6 Compatibility with Metals

Table of contents: Section B6: Compatibility with metals
Section	Subject	Page number
	Purpose and Scope	3
	Acknowledgements	3
	Summary	4
1	Introduction to Formate Brines	4
2	Introduction to Oilfield Corrosion	4
2.1	Types of Corrosion	4
2.2	Types of CRAs and how they are chosen	5
3	HPHT Field Experience	6
4	What Makes Formates less Corrosive than Other Brines?	7
5	The Carbonate/Bicarbonate pH Buffer in Formate Brines	7
5.1	How the Carbonate/Bicarbonate Buffer Works	7
5.2	Buffer Protection against CO2 (H2S) influx	8
6	Corrosion in Formate Brines in the Absence of Corrosive Gases	10
7	Corrosion in Formate Brines Contaminated with CO2	12
7.1	CO2 Corrosion	12
7.1.1	CO2 Corrosion of C-Steel	13
7.1.2	CO2 Corrosion of 13Cr Steel	14
7.1.3	CO2 Corrosion of Higher Alloy Steels	16
7.1.4	CO2 Corrosion Rates	16
7.2	Impact of CO2 on SCC	19
7.2.1	Testing by Hydro Corporate Research Centre	19
7.2.2	Testing by Statoil at Centro Sviluppo Materiali	20
8	Corrosion in Formate Brines Contaminated with H2S	21
8.1	Impact of H2S on General and Pitting Corrosion	21
8.2	Impact of H2S on SCC and SSC	21
8.2.1	Sulfide Stress Cracking (SSC) of Carbon and Low Alloy steels	21
8.2.2	Cracking of CRAs in H2S Containing Environments	22
8.2.3	High-Temperature Testing by CAPCIS	22
8.2.4	High-Temperature Testing by Statoil at Centro Sviluppo Materiali	24
8.2.5	Low-Temperature Testing by CAPCIS	24
8.3	Use of H2S Scavengers in Formate Brines	25
9	Corrosion in Formate Brines Contaminated with O2	26
9.1	Impact of O2 on SCC	26
9.1.1	Testing by Hydro Research	26
9.1.2	Testing by CAPCIS	27
9.1.3	Testing by Statoil at Centro Sviluppo Materiali	28
9.2	Use of O2 Scavengers in Formate Brines	28
10	Catalytic Decomposition of Formates – a Laboratory Phenomenon	29
11	Hydrogen Embrittlement of Metallic Materials in Formate Brines	30
11.1	Hydrogen Embrittlement	30
11.2	Sources of Hydrogen	30
11.2.1	Hydrogen Charging from Galvanic Coupling	30
11.2.2	Hydrogen Charging from Formate Decomposition	30
11.3	Field Evidence – Total’s Elgin Wells G1 and G3	31
12	Avoid Pitfalls in the Laboratory!	32
13	Avoid Pitfalls in the Field!	33
13.1	Four Simple Rules for Avoiding Corrosion in Formate Brines	33
13.2	Examples of Incorrect Use	33
	References	35