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Failure Analysis Of A Vacuum Pump Component In A Geothermal Power Plant

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This case study highlights the challenges facing designers of equipment required to operate in geothermal environments. It describes the failure of a non-condensable gas extraction pump at the Nga Awa Purua Power Station (NAP) which has a capacity of 140 MW. The station is located near Taupo in the North Island of New Zealand (Figure 1) and was commissioned in 2010.

Product Number: 51323-19044-SG
Author: Charles Thomas, Liam Rowlands, Keith Lichti, Nathan Gibson
Publication Date: 2023
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$20.00
$20.00

A cast stainless steel vacuum pump element failed after 10 years of service in a geothermal power plant where it was used to provide vacuum for operation of a direct contact condenser operating at 0.1 bar. The environment encountered included some wetness and non-condensable gases CO2, H2S, NH3 from the geothermal steam and some O2 derived from the recirculating cooling water taken from the cooling tower coldwell. The primary damage mechanisms were localized pitting corrosion and Stress Corrosion Cracking (SCC) in the aerated sulfur containing environment. The source of the stress was a combination of service loads and residual stress in the type 316 alloy CF8M (UNS J92900) casting. This paper provides a summary of the failure investigation work and compares the observed damage mechanisms with those seen previously in Slow Strain Rate tests in simulated geothermal power station recirculating cooling water and with heated U-Bends with a drip solution containing low levels of chloride and sulfide. Identification of the primary damage mechanisms facilitated the development of guidelines for determining the replacement material criteria.

A cast stainless steel vacuum pump element failed after 10 years of service in a geothermal power plant where it was used to provide vacuum for operation of a direct contact condenser operating at 0.1 bar. The environment encountered included some wetness and non-condensable gases CO2, H2S, NH3 from the geothermal steam and some O2 derived from the recirculating cooling water taken from the cooling tower coldwell. The primary damage mechanisms were localized pitting corrosion and Stress Corrosion Cracking (SCC) in the aerated sulfur containing environment. The source of the stress was a combination of service loads and residual stress in the type 316 alloy CF8M (UNS J92900) casting. This paper provides a summary of the failure investigation work and compares the observed damage mechanisms with those seen previously in Slow Strain Rate tests in simulated geothermal power station recirculating cooling water and with heated U-Bends with a drip solution containing low levels of chloride and sulfide. Identification of the primary damage mechanisms facilitated the development of guidelines for determining the replacement material criteria.

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Optimizing Sour Gas Qualification Testing – Modeling the Effects of Temperature and Total Pressure on H2S Fugacity, Activity, and Solubility Coefficients

Product Number: 51323-18762-SG
Author: Brent W.A. Sherar, Diana Miller, Hui Li
Publication Date: 2023
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Traditionally, sour severity of high-pressure, high temperature (HPHT) oil and gas production wells were assessed by H2S partial pressure (PH2S): The mole fraction of H2S in the gas (yH2S) multiplied by the total pressure (PT). While PH2S is appropriate for characterizing the sour severity of wellbores operating at low total pressures (e.g., PT < 35 MPa) and/or for highly sour systems (e.g., yH2S > 1 mol%), PH2S usually over-predicts the actual sour severity of HPHT systems, leading to sub-optimal material selection options. 
Picture for Methods to Assess Carburization Damage and Remaining Life in Fired Heater Tubes
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Methods to Assess Carburization Damage and Remaining Life in Fired Heater Tubes

Product Number: 51323-18771-SG
Author: Jeff Goldstein
Publication Date: 2023
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Fired heaters in coking service are susceptible to carburization damage, which needs to be predicted and managed to prevent unexpected downtime and expedited replacement costs. Carburization damage occurs when carbonaceous material, i.e., coke, is deposited on a steel surface and exposed to high metal temperatures; such are the internal conditions present in fired heater tubes in coking services. At these high temperatures, the carbon diffuses into the steel microstructure and increases the hardness while reducing ductility. At an advanced state, this reduction in ductility may lead to tube failure if a mechanical or thermal shock is applied. The diffusion of carbon can also cause the formation of deleterious chromium carbides in the steel microstructure, reducing the high temperature corrosion resistance in those areas.
Picture for Developing an Appropriate Heat Treatment Protocol for Additively Manufactured Alloy 718 for Oil and Gas Applications
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Developing an Appropriate Heat Treatment Protocol for Additively Manufactured Alloy 718 for Oil and Gas Applications

Product Number: 51323-18793-SG
Author: M.R. Stoudt, M.E. Williams, J.S. Zuback, K.W. Moon, C.E. Campbell, C.R. Beauchamp, M. Yunovich
Publication Date: 2023
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Additive manufacturing (AM) is a transformative technology that has opened areas of design space that were previously inaccessible by enabling the production of complex, three-dimensional parts and intricate geometries that were impractical to produce via traditional manufacturing methods. However, the extreme thermo-mechanical conditions in the AM build process (e.g., cooling rates ranging from 103 K/s
to 106 K/s and repeated heating/cooling cycles) generate deleterious microstructures with high residual stresses, and extreme compositional gradients.
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