Material selection for H2S and CO2 application

[metboss]

Dears,

In our upstream application, one of the Gate Valve of Wellhead equipment is found to be leaking after 3 years in service. Upon retrieval and post disassembly inspection, it was observed that seat pocket area, and seat were corroded with a significant metal loss. Also, there is evidence of erosion.
• The material grades are: Seat - AISI 410 (13%Cr) and Seat pocket area (part of valve body) - AISI 4130 75 KSI.
• Both Seat and Gate are hard-faced with Tungsten carbide material.
• Fluid characteristics are: H2S: 7-8 % & CO2 : 12-15%., Pressure rating: 3,000 psi

From material selection point of view, are above mentioned material grades (410 & 4130) suitable for service fluid contains 8% H2S and 15% CO2 ?
Apart from material compatibility, any other probable root cause?
Any recommendation for preventive action to avoid such recurrence in future?

Thank you,

 

[Dhurjati Sen]

Order new valve where seats are stellited, instead of hard facing by tungsten carbide alone.

DHURJATI SEN
Kolkata, India

 

[metboss]

Thank you Sen,
We have been using the Tungsten Carbide (GV70D/GV 50H) hard-facing since many years even bit stringent sour service applications and had no issues. Our concern is on raw material selection for Seat pocket which was machined out from Valve body (material grade AISI 4130) and Seat material (AISI 410: 13Cr in order to assess and avoid such recurrences in future.
Any alternative material in-lieu of 4130 material for seat pocket and 410 for seats considering H2S: 7-8 % & CO2 : 12-15%?

 

[Dhurjati Sen]

Valve body including seat pocket could be AISI 410 13 Cr instead of 4130.

Seat material AISI 347 instead of AISI 410. Hardfacing could be Tungsten carbide or stellite.


DHURJATI SEN
Kolkata, India

 

[SJones]

Ever thought about CRA weld overlay of pockets? If ISO 15156-3, Table A.23 has been used as a basis for selection of the stainless steel, you might want to review whether that grants sufficient cracking risk mitigation.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[metboss]

Thank you Sen and SJones for your valuable feedback.