High Collapse Casing

High Collapse Casing

Collapse & High Collapse Requirements

OCTG basically serves to maintain the well hole integrity during drilling, completion and production lifecycle of wells. Among them, the Casing, in particular, provides resistance to collapse caused by high-strength external load. The source of external load includes, pressure coming from stratum or reservoir flow in process of exploration and development, pressure from poor drillability mud and salt layer, mud system pressure, cement or seawater pressure under conductor or line pipe.

What is Collapse

Collapse resistance is a property of pipe body and defined as the limit exceeding which pipe fails in the circumferential direction when external pressure is applied.

Collapse calculation formulas were addressed in the API 5C3 or ISO 10400. Four failure modes have been defined based on failure pattern observation and mechanical rules (refer to figure below). These four domains are continuously positioned as a function of the ratio of the outside diameter to the wall thickness, or D/t ratio.

Influencing Factor

Collapse resistance is influenced by a complex combination of geometrical characteristics, material properties,
applied loads, and load conditions:

Geometry: Outer Diameter(D), Wall thickness(t),Ovality, Eccentricity or wall thickness variation.

Mechanical properties: Yield strength, Residual stress

Applied loads: Tension-Compression, Bending ,Torsion

Testing parameters: Length / D of tested sample, Parasite load due to testing equipment, Pressure gradient.

OAK high collapse casing covers full range from 4-1/2" to 13-3/8”in O.D.

Grades from 80ksi to 130ksi .

OAK-T Series: the collapse value greater than API 5C3.

OAK-TT Series: the collapse value greater than OAK-T Series for the same size.

OAK high collapse casings are designed by selecting and controlling the most influential parameters.

Also ,OAK high collapse casings are  delivered with the guarantee of their minimum  high collapse rating,for example : TP125TT(refer to figure below) .

On average ,OAK casing provides guaranteed High collapse performance values that exceed API by 20% to 35%.