News Details

1、 API 7K standard and core requirements for rotary excavation hose technology

The API 7K standard is a technical specification developed by the petroleum and natural gas industry for high-pressure fluid transmission hoses in drilling equipment, especially in the field of acid fracturing hoses used in conjunction with fire-resistant hydraulic blowout preventers and rotary drilling rigs. It imposes strict requirements on materials, performance, and testing methods. For acid fracturing conditions, the hose needs to withstand the impact of highly corrosive acid liquids (such as hydrochloric acid and hydrofluoric acid mixtures) with a sand content of 15% -25% and a pH value of 1-3, while meeting the instantaneous high pressure requirements of the fire-resistant hydraulic blowout preventer system.

 

（1） Structure and material requirements

Rotary excavation hoses usually adopt a multi-layer composite structure:

 

Inner rubber layer: It needs to have super wear resistance and acid corrosion resistance characteristics. The mainstream materials are hydrogenated nitrile rubber (HNBR) or fluororubber (FKM), with a Shore hardness of 70 ± 5 degrees and a tensile strength of ≥ 15MPa. After soaking in acid solution at 120 ℃ for 72 hours, the volume expansion rate is ≤ 5%. For example, in the acid fracturing operation of a certain oil field, a flexible hose with HNBR inner rubber layer was used. When transporting a 15% hydrochloric acid solution containing 20% quartz sand, the inner wall wear rate was reduced by 60% compared to traditional chloroprene rubber.

Reinforcement layer: composed of multiple layers of high-strength steel wire or aramid fiber weaving/winding, with steel wire tensile strength ≥ 2200MPa and aramid fiber fracture strength ≥ 28cN/dtex. API 7K requires the reinforcement layer to withstand a working pressure of at least 10000 psi (approximately 69 MPa) and a burst pressure of ≥ 3 times the working pressure. For example, a rotary excavator hose adopts a four layer steel wire cross winding structure and passes a blasting test under a pressure of 15000psi.

Fireproof layer and outer adhesive layer: The fireproof layer is coated with silicone rubber or ceramic fiber, and the flame retardant rating needs to reach UL94 V-0 standard. After continuous combustion in a flame at 800 ℃ for 30 seconds, the self extinguishing time should be ≤ 2 seconds. The outer rubber layer should be resistant to acid and alkali, and ozone. Chlorosulfonated polyethylene rubber (CSM) is usually used, with a Shore hardness of 65 ± 5 degrees and a UV aging resistance time of ≥ 1000 hours.

（2） Performance testing standards

API 7K specifies that hoses must pass the following tests:

 

Acid corrosion test: cycled in a 15% hydrochloric acid solution containing 20% sand at 120 ℃ for 200 hours, and the inner adhesive layer did not peel off or crack.

Wear resistance test: Using DIN 53516 standard, under the conditions of grinding wheel speed of 60rpm and load of 10N, the wear amount of the inner adhesive layer is tested to be ≤ 0.3mm/1000 revolutions.

Pulse test: Cycle 500000 times at 1.25 times the working pressure to simulate pressure fluctuations during acid fracturing process.

Fire test: According to ISO 15540 standard, the hose should be exposed to a flame at 800 ℃ for 30 seconds, and the structure should remain intact without leakage.

2、 Breakthrough in Ultra Wear Resistant Acid Fracturing Hose Technology and Manufacturer Practice

（1） Material Innovation and Process Optimization

Nano composite inner adhesive layer: An international manufacturer combines nano silica (SiO ₂) with HNBR to increase the hardness of the inner adhesive layer to 75 degrees and improve its wear resistance by 80%. In shale gas acidizing fracturing, the hose works continuously for 1200 hours without leakage, while the traditional hose has a lifespan of only 400 hours.

Aramid steel wire hybrid reinforcement layer: In response to the demand for ultra-high pressure, a certain enterprise has developed aramid fiber and steel wire hybrid winding technology. The aramid layer bears 30% of the load, while the steel wire layer bears 70% of the load. While maintaining a working pressure of 10000psi, the weight of the hose is reduced by 20%.

Ceramic coating fire prevention technology: using plasma spraying process, a 0.3mm thick alumina ceramic coating is formed on the outer layer of the hose, reducing the thermal conductivity to 0.5W/(m · K), and protecting the internal steel wire layer from thermal damage in a 1000 ℃ flame.

（2） Typical Manufacturer Case Analysis

Parker Hannifin Corporation, USA

The DrillFlex series rotary digging hose adopts a "Tri Layer" structure: the inner layer is a composite layer of fluororubber (FKM) and silicon carbide (SiC) particles, with an anti-wear performance of 0.1mm/1000 rpm according to DIN 53516 standard; The middle layer is a hybrid reinforcement layer of aramid steel wire, with a working pressure of 12000psi; The outer layer is a ceramic fiber fireproof layer, certified by UL94 V-0. This series of hoses has successfully completed 50 acid fracturing operations in deepwater drilling wells in the Gulf of Mexico, transporting over 100000 cubic meters of acid fluid.

ContiTech GmbH, Germany

Its "FireFlex" series hose integrates an intelligent monitoring system, embedding fiber optic sensors between the fireproof layer and the outer adhesive layer to monitor temperature, pressure, and leakage in real time. In the extreme working condition test of Beihai Oilfield, the hose was warned of the risk of inner rubber layer wear 12 hours in advance to avoid major accidents.

3、 Industry development trends and challenges

（1） Ultra high pressure and extreme working conditions demand

With the increase of deep and ultra deep well drilling, the working pressure of rotary drilling hoses is developing towards 15000psi (about 103MPa) or above. For example, the 15K series hose developed by a certain laboratory uses a six layer carbon fiber steel wire hybrid reinforcement layer, with a burst pressure of 60000psi, but the cost is 50% higher than traditional products and needs to be reduced through large-scale production.

 

（2） Environmental Protection and Sustainable Development

Application of bio based materials: A certain enterprise has developed a polylactic acid (PLA) based inner rubber layer, which maintains acid resistance while increasing biodegradability by 40%, making it suitable for offshore drilling with high environmental protection requirements.

Remanufacturing technology: Through processes such as cleaning, repairing the inner adhesive layer, and replacing the reinforcement layer, the performance of the old hose is restored to 80% of that of the new one. For example, a certain oil field has increased the utilization rate of waste hoses to 35% through remanufacturing technology, saving over 10 million yuan in annual costs.

（3） Intelligent and digital upgrading

Predictive maintenance: By embedding RFID chips or sensors in the hose, real-time monitoring of parameters such as pressure, temperature, bending times, etc., combined with AI algorithms to predict remaining life. For example, after adopting this technology, a certain oil service company reduced unplanned downtime of hoses by 60%.

3D printing customization: For special working conditions, rapid manufacturing of joints, flanges and other components through 3D printing can shorten the research and development cycle by 50%.

（4） Industry Challenges and Response Strategies

Cost performance balance: High performance materials such as ultra wear-resistant, fire-resistant, and acid resistant materials lead to increased costs, which need to be reduced through material substitution (such as aramid replacing some steel wires) and process optimization (such as continuous vulcanization process) to lower manufacturing costs.

Standards and certification barriers: API 7K certification has a long cycle and high cost, and small and medium-sized enterprises can enhance their competitiveness by cooperating with certification agencies and participating in standard development.

Supply chain risk: Key raw materials such as aramid fiber and carbon fiber rely on imports and need to strengthen domestic substitution research and development. For example, a certain enterprise has achieved mass production of T700 grade carbon fiber, breaking foreign monopolies.

In the future, the API 7K rotary digging hose for fireproof hydraulic spray preventers will develop towards ultra-high pressure, ultra wear resistance, intelligence, and environmental protection. Manufacturers need to continue to increase research and development investment, optimize materials and processes, and strengthen cooperation with oil service companies and research institutions to jointly address extreme working conditions such as shale gas and deep-sea oil and gas, and promote industry technological upgrading.