Krishnan_subbed.qxp 27/3/09 04:04 Page 71
Alloy K-500 – Past Failures in Downhole Completion Tools
Figure 3: Highly Scaled Alloy K-500 Circulation and Production Sleeve Figure 4: Alloy K-500 Safety Valve Landing Nipple that Failed
Component that Failed (Environment 3) But Did Not Show Much Corrosion Scaling (Environment 3)
decarburisation, the other source followed this primary melt practice measured as 38HRC. This was the only failure where there was any
by a secondary refining method known as electroslag re-melting. evidence that cold work could have been a contributing factor.
This latter method of refining is commonly specified for Alloy K-500
production today. As to the question of residual work, it was also Downhole environments for the failed components revealed a wide
observed that while some of the components that had experienced range of H
2
S partial pressures and pH, as shown in Figure 5. This
failures were manufactured from mill-supplied material (where figure also shows that some of the combinations of H
2
S partial
residual work is a possibility), others were re-annealed in-house pressure and pH in which failures were observed were, in fact, lower
following manufacturing operations. than the current limits of maximum H
2
S partial pressure placed on
the alloy in the NACE MR0175/ISO 15156 document. Failures were
Analysis of Alloy K-500 Failures also discovered to have occurred in environments with widely varied
The Alloy K-500 components that experienced failures in the field all temperatures. These observations led to the interim conclusion that
met the NACE MR0175/ISO 15156 requirement of 35HRC maximum Alloy K-500 is susceptible to failures at both low and high
hardness, except in one case where hardness near the fracture was temperatures in sour service, thus making it difficult to propose
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