Safety Relief Valves - Relief Valves

 Sub-Surface Safety Valves – API Practices for Equalizing and Opening

After the SCSSV tests successfully, use the following recommended reopening procedures.

a) SCSSVs with equalizing features:

  1. with external pressure source. Pressurize the tubing above the valve until the pump- through feature of the SCSSV functions to indicate the pressures are equalized. When equalized, slowly increase control-line pressure to the value recorded in step 1 or to the pressure established for normal operations.
  2. without external pressure source. With the well shut in, increase control pressure slowly until the tubing pressure begins to increase. Close the manifold control valve and record the opening pressure. When the tubing pressure stabilizes, pressurize the control system to open the SCSSV. Increase the hydraulic control-line pressure to the value recorded in step 1, or to at least 3,45 MPa (500 psi) greater than the opening pressure.

b) SCSSVs without equalizing features:

An external pressure source should be used to equalize the pressure across the SCSSV before opening. When equalized, slowly increase control-line pressure to the value recorded in step 1 or to the pressure established for normal operations

Tubing Retrievable

This model of safety valve is installed as an integral part of the tubing string. Hydraulic operating fluid is supplied via a stainless steel control line which is strapped to the tubing and terminates in the production wellhead.

In the event of valve failure, the valve can be put out of service by wireline means and a wireline retrievable safety valve installed in the tubing nipple. This allows production to continue and postpones the inevitable workover to replace the tubing valve.

Wireline Retrievable – Direct Controlled

Direct controlled safety valves, which are normally open valves, rely on changes in flow through the valve to close the valve. The J Storm Choke incorporates a ball flow bean – the bean also serving as the ball seat. The spring serves to hold the valve in the open position. Should a sudden drop in pressure takes place above the bean, the differential pressure across the bean overcomes the spring tension causing the flow tube to move upwards. This causes the ball to roll to the closed position.

Landing nipples serve as receptacles for lock mandrels. Attached to the lock mandrel is some sort of flow control device. Flow control devices are tools such as tubing plugs (pump thru and positive), downhole safety valves (direct and remotely controlled), and downhole chokes, just to name a few.

If there are multiple nipples in the production string, the wireline operator must be able to select which nipple he is to set the lock mandrel and flow control device.

Subsurface Safety Valves – Wireline Retrievable – Tubing Nipples

The  “standard” R  Safety  Valve  Nipple  is  internally  machined  to accept an R lock mandrel. It also has a polished bore in which the packing on the mandrel effects a seal.

As seen in the illustration, a control line is made up to the nipple through which hydraulic fluid is pumped to open the safety valve.

The X Sliding Sleeve Nipple incorporates a sliding sleeve which serves to cover the control line opening when the safety valve is pulled from the nipple. This prevents wellbore particulates from entering the opening to the control line and possibly plugging the control line. When the valve is re-set the sleeve is shifted before the lock mandrel lands and sets in the nipple profile. The shifting tool is made up between the lock mandrel and the safety valve.

Otis Type S equipment allows nipple selection via the profile of the nipple. The locator mandrel (at left) uses locator keys which are machined to match a profile cut in the lower part of the nipple (locator profile). The nipple/mandrel combination is available in 5 “positions” which are based on the machining of the locator profile of the nipple and the corresponding locator keys.

The order of installing S nipples in the tubing is Pos. 1, Pos. 2, Pos. 3, etc. If a NoGo nipple is to be used it’s installed in the tubing before Pos. 

Otis Type S & T equipment is set and

locked as shown at right.

The spring-loaded locator keys compress as  they  enter  the  nipple  and  then  “pop” out  and  “seat” as  they  enter  the  locator profile.


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