Meeting valve reliability challenges on SAGD projects
A major operator in Alberta was challenged with valve reliability issues relating to the process properties presented by the SAGD (steam assisted gravity drainage). Valves on SAGD processes face distinct challenges. Steam service requires valves with long lasting zero leakage to avoid trim damage from high velocities. Emulsion service requires valves that can withstand abrasive impurities. Poor valve choices result in long term reliability issues and higher maintenance costs. A technical review of valve designs was conducted by the EPC to determine the best design for each service.
Advanced Engineering Valve (AEV) developed the 2XC (double eccentric) C-Ball valve to overcome deficiencies in standard metal seated ball valves related to wear, abrasion, and long-lasting tight shutoff.
The unique design of the 2XC eliminates normal wear and friction found in metal seated ball valves by a cam-style motion to close through a double offset in stem position. This avoids grinding the valve trim together which in the presence of abrasive impurities will quickly lead to leakage and/or failure.
2XC sealing energy is mechanical/torque sealing rather than relying on springs and process pressure as in standard metal seated ball valves.
2XC, having no springs, and using Belleville washers in the process completely eliminates concerns related to abrasive impurities inherent in emulsion service. Spring/Belleville contamination of standard metal seated ball valves leads directly to valve seizure and early failure compromising process reliability.
The 2XC seal is mechanically generated through torque sealing. This provides bi-directional tight shutoff without relying on springs or process pressure meaning closure is certain and reliable even with low pressure differentials. ISO 5208 Rate A Zero Leakage (bubble tight) Metal to Metal and no friction design provides long lasting tight shutoff leading to long term reliability even on steam service.
A standard metal seated ball valve has cavities between the ball and the body that are sealed by the seats. When the valve moves from open to close these areas fill with the process. When the valve is in an open or closed position these are dead spaces where the process can harden.
The 2XC C-Ball shape eliminates the ball cavity allowing the process to be separated into upstream and downstream. There are no dead spaces. On emulsion service this prevents the pulling of abrasive fines across the sealing surface. On steam service this prevents condensate from being trapped behind the ball and damaging the valve when expanding back into steam.
Standard metal seated ball valves have hard coating on the surface of the ball for anti gall and wear resistance. Full ball geometry does not allow the internal bore of valve to be coated. This seam is a weak spot that is presented to the highest velocity of the SAGD process every time the valve is moved from open to closed position.
The 2XC open “C” geometry lends itself naturally to 100 percent hard coating. This eliminates weak spots, especially at small degrees of opening where high velocity erosive damage occurs.
These innovations allowed the operator to select a single valve that is reliable on both emulsion and steam service for a SAGD process. By identifying a single valve that has the ideal attributes necessary for long term reliability future maintenance is simplified and reduced.
A number of key attributes were identified by the operator: abrasive issues were dealt with at root cause, an evolutionary simple design was used, there are no springs or Belleville washers, nor hard coat seams.
The valve has no ball cavity or friction cam motion. It is rated ISO 5208 Rate A Zero Leakage, and seals independent of springs or process pressure.