Method for evaluating critical stress intensity and sensitive factor of stress corrosion cracking for oil well pipe

Abstract

The invention discloses a method for measuring the oil well pipe corrosion cracking critical stress intensity and sensitive factor. It adopts U-type loading hook to do static loading-unloading closed loop movement to the pin-and-hole of the twin cantilever (DCB) sample before and after the sulfide stress corrosion cracking test, makes the firmer chisel, loads the DCB perpetuity shift sample and obtains the loading and the relate curve of the shift at the same time; it quantity measures the DCB sample firmer chisel initial level loading, firmer chisel loading DCB actual cantilever shift and the critical level loading value after the test.

Description

(1) Technical field [0001] The invention relates to an evaluation method for critical stress intensity and sensitivity factors of oil well pipe stress corrosion cracking. The method is to prepare a high-strength sulfur-resistant oil well tubular double cantilever beam sample (DCB sample) on the hardware platform of a general dynamic material testing machine, and evaluate its critical stress intensity factor (hereinafter referred to as DCB sample) under sulfide stress corrosion or environmental corrosion conditions. K 1SCC index) and sensitivity factor ΔK. This method is also applicable to the detection of corrosion-resistant steel, stainless steel and other products. (2) Background technology [0002] The test method for the stress corrosion cracking resistance of oil well pipes under high sulfide service conditions has been issued by the American Society of Corrosion Engineering (NACE) A set of test standards (NACETM0177-1996), which regulates the evaluation of metals und...

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Problems solved by technology

However, on how to measure and control fatigue crack growth, NACE and IRP did not publish standardized program terms, but only stipulated the load range and vibration frequency of pull-pull cyclic loading, which directly affected the high-strength sulfur-resistant oil well pipe K 1SCC Index determination and subsequent quantitative research on the relationship between fatigue crack length and critical stress intensity factor

Due to the particularity of the DCB sample, it cannot yet be classified into the sample types listed in ASTM E647, and the flexibility algorithm published by the standard is adopted.

Moreover, the flexibility adopted in the ASTM E647 standard is based on the ratio of the measured value of the cantilever opening displacement COD extensometer to the load, which requires adding a dovetail groove to the end of the cantilever, which is undoubtedly quite different from the processing requirements of NACE for the sample.

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