API 16A - STRESS CALCULATIONS FOR SOLID CONNECTING SHAFT WITHIN WELLBORE

[bawest47232]

Forgive me if I ask this incorrectly, but I have a question about a ram shaft, seal seat insert in the body, ram blocks. Are these required to be analyzed per API 6X because they are pressure-controlling? We consider the ram shaft to be pressure containing and controlling but the stresses on the ram shaft are not working in tension and the components listed above are not acting as a pressure-containing or controlling component except where they seal against the bonnet, the body or themselves. In all of the instances, the primary stresses are working to compress the material or in the case of the shaft, the forces work to buckle the component.

Since API 6X only allows for tensile yield, some components will need to be designed with higher yield material although the buckling strength is sufficient. ASME BPVC allows for consideration of buckling in these situations, but it looks like API 16A does not differentiate between compressive/buckling versus tensile yield. It seems like we are evaluating the ram shaft as a pressure vessel when there is no pressure differential on the solid shaft.

Maybe I am not understanding this since I am not a stress engineer, but our stress analysis team is rejecting the design because the part yields when in reality, it would be acceptable as is.

API 16A SECTION 4.4.2 PRESSURE CONTAINING, PRESSURE CONTROLLING, PRESSURE RETAINING PARTS ARE TO BE DESIGNED PER API 6X.

 

[NRP99]

I am not well conversant with drill-through equipment and standards associated with it. Below is just my code interpretation.

API 6X has similar requirements as in ASME BPVC Section VIII Div-2 Part 5.

Refer scope section of API 16A and components to which it is applicable- ram blowout preventers, ram block, packers and top seals. Also read terms and definitions-3.1.61 to 3.1.67 for more understanding of the terms- pressure containing/retaining/controlling.