Inner BOP Seals: Primary Wellbore Barriers
Inner BOP Seals serve as the primary sealing elements within Blowout Preventers (BOPs), forming the first line of defense against uncontrolled hydrocarbon release. Typically constructed from high-durometer elastomers (hydrogenated nitrile/HNBR or FKM) reinforced with steel fabric or aramid plies, these seals provide zero-leakage containment under pressures up to 15,000 psi (103 MPa) and temperatures from -30°C to 220°C.
The inner seal energizes through hydraulic piston activation, creating uniform radial compression that conforms to irregular pipe OD variations (±10%) and withstands 500+ actuation cycles. These seals excel in ram-type BOPs (blind, pipe, variable bore) and annular preventers, meeting API 16A PSL 3 requirements with NACE MR0175 sour service certification.
Inner BOP Seal Types and Specifications
| Seal Type | Material Composition | Pressure Rating (psi) | Temp Range (°C) | Bore Compatibility (inches) |
|---|---|---|---|---|
| Blind Ram Inner | HNBR + steel fabric | 10,000 | -20 to 180 | Full bore closure |
| Pipe Ram Inner | FKM + aramid cord | 7,500 | -30 to 200 | 3-1/2 to 8-1/2 pipe |
| Variable Bore | Multi-durometer HNBR | 5,000-10,000 | -20 to 150 | 2-3/8 to 7 OD range |
| Spherical Inner | Urethane/elastomer hybrid | 15,000 | -10 to 220 | Annular BOP elements |
Material Properties for Inner Seals
| Compound | Hardness (Shore A) | Tensile Strength (MPa) | Elongation (%) | H2S Resistance | API 16A Tested Cycles |
|---|---|---|---|---|---|
| HNBR Standard | 85-95 | 18-25 | 300-450 | Excellent | 500+ |
| FKM High-Temp | 90-100 | 15-20 | 200-300 | Superior | 400+ |
| Aramid Reinforced | 90-95 | 25+ | 250-350 | Excellent | 600+ |
| Low-Temp HNBR | 80-90 | 20-22 | 400-500 | Good | 300+ |
Standard Bore Size Compatibility
| BOP Bore Size (inches) | Inner Seal Part No. | Pipe OD Range (inches) | Activation Pressure (psi) |
|---|---|---|---|
| 7-1/16 | IBS-0716-35 | 3-1/2 to 5-1/2 | 1,500-3,000 |
| 11 | IBS-1100-45 | 4-1/2 to 7 | 2,000-4,000 |
| 13-5/8 | IBS-1358-55 | 5 to 8-1/2 | 2,500-5,000 |
| 18-3/4 | IBS-1875-65 | 6-5/8 to 10 | 3,000-6,000 |
Performance Requirements (API 16A)
| Test Requirement | Acceptance Criteria |
|---|---|
| Pressure Test | No visible leak @ 1.5x rating |
| Cyclic Actuation | 500 cycles minimum |
| Explosive Decompression | Class X EDS 10.4 compliant |
| Sour Service (H2S) | NACE MR0175/ISO 15156 |
| Low Temperature | TR-E @ -20°C |
Inner BOP seals feature proprietary chevron-style energization profiles that maintain contact stress >800 psi across the sealing surface, preventing extrusion gaps even after repeated pressure reversals. Steel reinforcement plies (0.5-1.0 mm thick) prevent fatigue cracking under 10 million flex cycles.