Peter Sharpe Talks: Rotary Shouldered Connection (RSC) Failures and Causes
Rotary Shouldered Connection (RSC) Failures and Causes.
By Peter Sharpe – CEO Sharpe Engineering
Seal or Shoulder Damage
Seal or shoulder damage is the most common damage to Rotary Shouldered Connections and is the most overlooked. A damaged shoulder or seal can be catastrophic, and in a very short time lead to connection failure and ultimately an expensive fishing operation.
The most common causes of Seal / Shoulder damage are;
1. Improper Make-up Torque
Too little make-up torque (MUT) is the most common cause of shoulder damage. Connections that are not correctly tightened invite drilling fluid to pass between the shoulders when the drill string is working. This in turn, erodes the shoulder seal and ultimately the entire connection (see picture accompanying this article).
Insufficient make-up torque will also cause the lubrication (pipe dope) to wash away from the shoulders whilst the drill string is working. This is evident when high break-out torque is experienced and subsequent galling on the shoulders is evident. If the shoulder is not repaired or joint is not laid out from the working string, this will damage the shoulder seal of the next connection that is made up to the damaged one.
2. Handling and Stabbing Damage.
Improper handling can damage the shoulder seal of the connection. Visual inspection to identify any damage is paramount before connection is doped and proper make-up torque is applied. Clean connections thoroughly and ensure fresh uncontaminated dope is applied evenly to pin and box connections immediately prior to make-up.
How to Effect Repairs to Damaged Shoulder Seals
1. In-Lathe (shop) refacing
In-Lathe or machine shop refaced connections are machined with the axis of the connection set up running true and subsequent seal and shoulder is machined flat and at right angles to the entire connection.
The connection can also be gauged to ensure correct stand-off after refacing.
In-lathe refaces are also anti-gall treated for added shoulder/seal protection from galling on the initial make-up.
2. In-Field Refacing
In-field refacing of connections are generally performed when a pipe inspection company is performing a rack inspection of drill pipe or BHA at the rig site. This process is normally done to remove minor scratches, galling and imperfections from the shoulder seal face.
The refacing tool is made-up onto the threaded portion of the connection and is reliant on the connection axis being at right angles to the seal/ shoulder face.
In-field refacing in no way emulates or replaces an in-lathe reface in the machine shop (see above) and should not be performed when shoulder damage is significant. Doing so could compromise shoulder flatness and negatively affect shoulder torque. Shoulder flatness and surface finish is also dependent on the type of in-field refacing equipment used and may not meet the required applicable standards.