The specifications are essential part of purchase orders. The following article provides an overview of what are the various requirements to be considered while specifying the equipment for purchase. The article also gives an overview of technical requirement and specification of the casing, tubing, wellhead componenets and christmas tree.
CASING AND TUBING
| DESCRIPTION | CASING | TUBING |
|---|---|---|
| Function | Casing is hollow metal pipe inserted in to the drill hole called “CASING” to protect and support the well stream. | Tubing is pipe centered in the annulus of an oil and / or gas well through which hydrocarbons flow to the surface from the formation. |
| Design Consideration (Note 1) | Tensile force, Burst pressure, Collapse pressure and Combined stresses. | Internal yield pressure, Joint or body yield strength and Collapse resistance |
| API Outside Diameter (OD) in Inches (Note 2) | 4.5 5.0, 5.5 6.0, 6.625 7.0, 7.625, 7.75 8.625, 8.75 9.625, 9.75, 9.875 10.75 11.75, 11.875 13.375, 13.5 & 13.625 |
0.75 1.0, 1.25, 1.5 2.0625, 2.375, 2.875 3.50 4.0, 4.50 |
| Wall Thickness | The API casing is manufactured in various thicknesses for each OD. However Outside Diameter of sizes 7.75, 8.75, 9.75, 9.875, 11.875, 13.5 and 13.625 is manufactured with only one thickness. | The API tubing is manufactured in various thicknesses for each OD. However Outside Diameter of sizes 0.75, 1, 2.0625 and 4.5 is manufactured with only one thickness. |
| Length in Feet (Note 3) | Range R1 – 16 to 25 ft Average: 22 ft Range R2 - 25 to 34 ft, Average: 31 ft Range R3 – > 34 ft, Average: 41 ft |
Range R1 – 20 to 24 ft Range R2 – 28 to 32 ft (Normally Used) |
| End Connections | STC – API short round thread LTC – API long round thread Buttress thread VAM Thread Extreme Line threaded coupling Metal to Metal seal T&C Integral joint connection |
External Upset Tubing & Coupling (EUE) Non Upset Tubing & Coupling (NUE) Integral Joint Tubing (For sizes up to 2.0625 inches only) |
| Steel Grades | See below table. | |
| STANDARDS (Note 4) | API 5CT - Specification for Casing and Tubing ISO 11960:2004-Petroleum and natural gas industries-Steel pipes for use as casing tubing for wells |
|
Notes
- The API design factor of 1.8, 1.125 and 1.1 is used for tension & joint strength, collapse pressure and burst pressure respectively.
- Drift diameter is also specified along with the OD, Drift diameter is the diameter of a cylindrical mandrel that can pass through freely through the casing with a reasonable exerted force equivalent to weight of the mandrel.
- Tubing pup joints commonly used comes in 2, 3, 4, 6, 8, 10 and 12 feet lengths.
- The API and ISO standards govern the characteristics of Oil Country Tubular Goods (OCTG). OCTG refers to a class of specialized steel pipe used in oil and gas extraction, mostly seamless and welded. OCTG standards are API standard eeffectively governed world-wide by API Sub-Committee 5 (SC5) documents with varying levels of supplementary specifications from individual companies.
The following table lists the various grades used for cabing and tubing manufacture.
| Grade | Yield Strength (Min – Max, psi) | Min. Tensile Strength (psi) | Remarks |
|---|---|---|---|
| H-40 | 40,000 – 80,000 | 60,000 | H40 is a carbon type steel which is the lowest strength casing and tubing grade in the OCTG Specifications. The maximum yield strength assures suitability for use in hydrogen sulphide service (H2S). |
| J-55 | 55,000 – 80,000 | 75,000 | J55 is a carbon type steel and is both tubing and casing grade. The maximum yield strength assures suitability for use in hydrogen sulphide service (H2S). The API equation for joint strength for tubing includes only yield strength excluding tensile strength, hence J55 is used for tubing. |
| K-55 | 55,000 – 80,000 | 95,000 | K-55 is a casing grade only also classified as carbon type steel. K-55 was developed after J-55 and has a higher tensile strength. In fact, the collapse and internal yield strengths of both grades are identical. But due to the higher tensile strength, K-55 has a casing joint strength higher than J-55. K-55 is considered suitable for hydrogen sulphide service (H2S) at all temperatures. |
| L-80 | 80,000 – 95,000 | 95,000 | L-80 is both casing and tubing grade most widely used high strength grade for H2S service. The method of manufacture can be either ERW or Seamless and the steel must be quench and tempered. L-80 was the first grade to have a max. Hardness requirement, Rockwell G23. |
| N-80 | 80,000 – 110,000 | 100,000 | Is the highest strength grade in Group 1. N-80 is classified as an alloy steel. N-80 is not considered suitable for H2S service at temperatures above 150 deg F for quenched and tempered steel and above 175 deg F for normalized steel. |
| C-90 | 90,000 – 105,000 | 100,000 | C-90 has increased usage in critical high pressure wells containing H2S. C-90 is both tubing and casing grade. The method of manufacture is specified as seamless with the chemistry alloy steel (containing chromium and molybdenum) for added toughness. Maximum hardness is restricted to Rockwell G25.4. |
| C-95 | 90,000 – 105,000 | 110,000 | C-95 is casing grade only was placed in specs after early success with use of restricted yield strength for grade C-75 (discontinued by API). The process of manufacture can be ERW or seamless, and the steel type is alloy. Despite the earlier successes with C75 and its restricted yield strength, C95 was found to be not suitable for H2S at lower temperatures due to the higher strength levels permitted. API did not give C95 a hardness limitation In part due to the popularity of grades such as Lone Star Steel’s S-95, very little C95 is purchased today. |
| T-95 | 95,000 – 110,000 | 105,000 | T-95 modeled after C-90 solves the problems encountered with C95 in H2S. T-95 is both tubing and casing grade. The method of manufacture is specified as seamless with the chemistry an alloy steel. Maximum hardness is restricted to Rockwell G25.4. |
| P-110 | 110,000 – 140,000 | 125,000 | P-110 is a tubing and casing grade (since P-105 is discontinued as tubing grade by API). The process of manufacture is both ERW and seamless for casing, and seamless for tubing. When P110 was created, it was thought that this grade would handle all future deep drilling requirements. However, drilling depths and pressures continue to increase, and higher grades are now in regular use. |
| Q-125 | 125,000 – 150,000 | 135,000 | Q-125 is used in wells with very high pressures and for large OD casing with significant collapse forces. The grade is classified as Group 4. The process of manufacture is both ERW and seamless for casing sizes. Q125 was the first API grade to require impact tests to confirm steel toughness. NACE included what amounts to Q125 Type 1 in its specification for H2S service, but only at temperatures of 225 deg F and hotter. |
| V-150 | 150,000 – 180,000 | 160,000 | V-150 is not an API grade. It is not rated for H2S service at any temperature. Commercially it is very uncommon. |
Grade Source Info: Octg Products
WELLHEAD COMPONENTS AND CHRISTMAS TREE
| Description | Specification |
|---|---|
| Pressure Rating | 2,000 psi 3,000 psi 5,000 psi 10,000 psi 15,000 psi 20,000 psi 30,000 psi |
| Temperature Class | K - 60 to 82 deg C L - 46 to 82 deg C N - 46 to 60 deg C P - 29 to 82 deg C R – Room Temperature S - 18 to 60 deg C T - 18 to 82 deg C U - 18 to 121 deg C V 2 to 121 deg C X -18 to 177 deg C (Non standard rating) Y -18 to 343 deg C (Non standard rating) |
| Material Class | AA, BB and CC – General Service DD, EE, FF, HH – Sour Service requires compliance to NACE MR0175 / ISO 15156. Along with material class maximum allowable H2S partial pressure in psi 0.5, 1.5 and NL (No limit) is required to be specified. ZZ – User Defined. |
| Product Specification Level (PSL) | PSL-1 equipmentshall meet the minimum requirements of API Spec 6A for design, specification, and qualification Charpy V Notch (CVN ) testing for service temperature -50 deg F and below), Process, inspection and hydrostatic test (except for loose connectors).
PSL-2 equipment:In addition to requirements of API Spec 6A PSL-1, PSL2 equipment controls the limits of variance between the material qualification test coupon and the production material. CVN testing for service temperature -20 deg F and below, volumetric inspection of welds (RT or UT), MPI of accessible well wetted parts. PSL3 equipment:In addition to requirements of API Spec 6A PSL-2, PSL-3 equipment restricts the tolerance of material chemistry, increases the maximum size of the material qualification test coupon in relation to the section thickness of equipment, CVN testing for all service temperatures, volumetric inspection of all material, Wet MPI of accessible well wetted parts, Hydrostatic test time extended. PSL3G equipmentIn addition to requirements of API Spec 6A PSL-3, PSL3G equipment includes additional practices described in API Spec 6A Annex A. Additional gas testing requirement for assembled equipment. PSL4 equipmentIn addition to requirements of API Spec 6A PSL-3, PSL4 equipment increases the maximum size of the material qualification test coupon in relation to the section thickness of equipment, prohibits welding except for overlay / inlay of corrosion resistant alloy on well wetted surfaces, Gas testing of assembled equipment. |
| Performance Requirements (PR) | PR1 is minimum API cycle requirements found in the equipment section of the spec 6A PR2 adds additional cycles. |
| End Connections | Threaded connections components are directly threaded onto the previous component. They are typically used only in lower pressures, sweet operations and for smaller diameter pipe or fittings.
Welded connections are the weld itself that provides both a solid connection and sealing between components. With wellheads, Fillet welds often are used to connect pipes or fittings of dissimilar diameters in a socket or slip-on configuration. A butt weld is used in most other welding applications such as connecting two lengths of pipe of the same unit weight (kg/m) and diameter. Flanged connections involve two flanges bolted together on the exterior of the component housing. Each flange has a ring groove and the connection is made up with a ring gasket to enable a seal between the flanges. Studded connections involve one component that has studs threaded into its housing and a second component with a flange bolted to the studs. Like flanged connections, studded connections include a ring groove and are made up with a ring gasket to create a seal between the components. Clamp Hub Connections is the enlarged end of a wellhead component that will be used to make a connection. With a clamp hub connection, the hubs of the two components being joined are squeezed together over a seal ring or ring gasket and held in-place by a clamp. The two clamp halves wrap around the hub and are bolted to each other to a specified torque to provide the required connection strength and seal rating. Most commonly used in thermal operations. |
| Standard | API 6A – Specification for Wellhead and Christmas Tree Equipment |
API SPECIFICATIONS
The following table lists some of the most commonly used API specifications which serves as a guideline while specifying purchasers requirement for procurement of drilling, casing, tubing, wellhead and Christmas tree equipment.
| API Spec | Description |
|---|---|
| API Spec 5CT | Specification for Casing and Tubing |
| API Spec 5D | Specification for Drill Pipe |
| API Spec 5L | Specification for Line Pipe |
| API Spec 6A | Specification for Wellhead and Christmas Tree Equipment |
| API Spec 6D | Specification for Pipeline Valves |
| API Spec 6H | Specification for End Closures, Connectors and Swivels |
| API Spec 7-1 | Specification for Rotary Drill Stem Elements |
| API Spec 7K | Specification for Drilling and Well Servicing Equipment |
| API Spec 8A | Specification for Drilling and Production Hoisting Equipment |
| API Spec 8C | Specification for Drilling and Production Hoisting Equipment (PSL1 and PSL 2) |
| API Spec 9A | Specification for Wire Rope |
| API Spec 11B | Specification for Sucker Rods |
| API Spec 12B | Specification for Bolted Tanks for Storage of Production Liquids |
| API Spec 12D | Specification for Welded Tanks for Storage of Production Liquids |
| API Spec 12F | Shop Welded Tanks for Storage of Production Liquids |
| API Spec 12P | Specification for Fiberglass Reinforced Plastic Tanks |
| API Spec 14L | Specification for Lock Mandrels and Landing Nipples |
| API Spec 16D | Specification for Control Systems for Drilling Well Control Equipment and Control Systems for for Diverter Equipment |
