High collapse casing to be used in high pressure wells. As mechanical properties and pipe dimensions are major factors in collapse resistance, the following parameters have been optimised to guarantee high collapse pressures: D/t ratio, yield strength, ovality, wall thickness, residual stresses.
Unitesteel provides the High Collapse Series of proprietary steel grades for oil and gas wells where high external pressures are anticipated and collapse resistances higher than API are needed.
In addition to uniform external pressures, the reservoir can exert high pressures due to ground movements or saline strata, subjecting pipes to extreme localized external pressure.
Our Series is available in minimum yield strengths ranging from 80Ksi to 140Ksi. These products have higher guaranteed collapse pressure than that determined by API 5CT/ISO 11960 products.
PARAMETERS FOR EXCELLENT COLLAPSE PERFORMANCE
The collapse of a pipe is related to the stiffness or rigidity of its cross section area along the pipe length. Dimensional and mechanical properties determine a true high collapse proprietary product. We pay strict attention to these variables when producing our Series.
DIMENSIONAL PROPERTIES
The dimensional properties of a high collapse pipe depend on three factors: external diameter to wall thickness ratio, ovality and eccentricity. Low ovality, low eccentricity and the maximum wall thickness for the maximum allowed pipe weight will give the best dimensional conditions for collapse resistance.
MECHANICAL PROPERTIES
The mechanical properties that determine high collapse are yield strength and residual stresses. Strict control of the heat treatment process to ensure optimum yield strength distribution and minimal compressive residual stresses will lead to the maximum collapse properties of the pipe.
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