THE SUPERPOSITION PRINCIPLE OF COM- BINED LOADS IN STRENGTH ANALYSIS SIX IMPORTANT ISSUES ABOUT DESIGN IN STRESS ANALYSIS FOR PRESSURE VESSELS （PART 2）;DESIGN AND CALCULATION OF FLOATING PARTS IN SINGLE-TUBE PASS FLOATING HEAD HEAT EXCHANGER

The different loads in pressure vessels may lead to primary stress,secondary stress and peak stress.According to the failure modes of these three kinds of stress,this paper discusses the superposition principle of these stresses caused by pressure,gravity,wind and earthquake.And it points out that the primary stresses caused by combined loads shall be added together;secondary stresses caused by pressure,gravity,wind and earthquake shall not be added together;they shall meet the stability principle separately;peak stresses shall be added together according to cumulative damage.

Many types of single-tube pass floating head heat exchanger have been applied in petrochemical units for many years.According to the connecting structure between the tube channel outlet pipe at the floating head and rear shell cover,this article sums up the three structure types in engineering.For the commonly used type of the annular clamping plate and the flange with external gasket connecting structure,the article gives the detailed mechanical analysis based on the interaction between the annular clamping plate and the flange with external gasket and design formulas so as to realize the more accurate engineering design and calculation.

This paper compares and studies the flow characteristics of the standard elliptic section on the twisted tube heat exchanger with different torques by using three-dimensional numerical simulation method of Computational Fluid Dynamics（CFD）.It analyzes the effects oftwisted tube with different torques on the performance of heat exchanger with the same design parameters.The results show that the optimal performance of heat exchange tube with 9times the equivalent（long axis）diameter of torque can be achieved if the heat transfer coefficient（α=K/（ΔP/L））of pressure loss per unit is taken as the criterion under the condition of the same inlet velocity and outlet pressure.This provides some reference for the optimization design and scientific research of heat exchanger with twisted tubes in engineering application.

This paper provides two approaches to calculate tube sheet stress and stress of heat exchange tube corresponding to the effective thickness of the tube sheet of floating head heat exchanger.The first approach is an iterative method for solving the tube sheet stress by using the C curve in GB/T 151 and then obtaining the stress of heat exchange tube;the second approach is to solve the tube sheet stress directly by using the fri curve and mt curve in GB/T 151 and then obtain the stress of heat exchange tube.In engineering practice,these two approaches can be used to calculate the actual stress of the tube sheet and heat exchange tube according to the actual effective thickness of the tube sheet so as to make engineering evaluation on the thickness of the tube sheet.

Sewage tanks have been widely used in petrochemical enterprises.Since the components of the sewage medium during production process are complex with flammable,explosive and corrosive medium containing sulfur and oil,these bring certain safety risks to production.This paper aims at the deflagration accident of acid water tank in Yangzi Petrochemical Co.,Ltd.on June 9,2014 and discusses the existing safety risks of the sewage tanks in petrochemical enterprises from the perspective of intrinsic safety.Then it puts forward the solutions.

This paper analyzes the reasons for the three cracking of bundles and tube sheets in the cycle oil slurry steam generator in SINOPEC Cangzhou Company.It is found out that the unplanned downtime of the unit,the recovery process and the pump failure resulted in the abnormal fluctuation of the oil slurry flow and the temperature which led to stress corrosion cracking of the tube sheet.The paper then brings forward corresponding countermeasures from such aspects as optimizing production operation,revamping equipment and so on.

Through analyzing the causes and hazards of water hammer produced by traditional old heater,this paper describes the working principles,structure and engineering application of the first generation water-hammerless energy-saving heater as well as the existing problems and shortcomings during its application.Meanwhile,it expatiates on the unique advantages of the new all butt joints water-hammerless energy-efficient tank heater.Theoretical analysis and practical application show that：compared with traditional heater,the water-hammerless tank heater eliminates the water hammer phenomenon in operation,featuring better heating effect,higher heating speed,less steam consumption,and more obvious energy-saving effect;and the new all butt joints waterhammerless energy-efficient tank heater solves the bottleneck problem of production quality which exists in the first generation water-hammerless heater,being more durable and widely used.Therefore,the new all butt joints water-hammerless heater represents the development direction of tank heating facilities.

This paper introduces the expansion joint failure of the 410t/h boiler ignition air duct in a factory and treatment measures from three aspects covering equipment manufacture,installation and process operation.According to the provisions of the technical agreement,the metal material performance of the joint point contacting flue gas directly shall not be lower than 0Cr25Ni20Si2.But ordinary stainless steel was used in the manufacturing process.During the installation process,the pre-dislocation amount of 80 mm was not set aside according to the design requirements,resulting in serious bellow deformation of expansion joint,internal casting material damage and falling off in the operation process.During ignition,the rated capacity of the burner oil gun was too large;the atomizing air pressure was too low;the oil combustion of light diesel was insufficient;the temperature of combustion chamber connected by expansion joints was higher than the design temperature;high-temperature flue gas entered into the expansion joint bellows.And these eventually led to expansion joint breakdown.After the breakdown,the expansion joints were rectified and repair welding was carried out;the damaged anchor nail and casting material were repaired.After ignition,the boiler met the needs of operation.It＇s suggested that expansion joint shall be designed and manufactured again according to the actual situation of the boiler installation and operation parameters;new type of seal shall be used to avoid the high-temperature flue gas entering the corrugated tube parts.

Cracks occur frequently around the two pairs of welding neck flange at the short inlet cone section of the FCC flue gas turbine in certain petrochemical company in recent years.So there＇re hidden dangers of weld fracture.There＇s serious flange deformation inside the short section.The flange clearance is decreased from 8mm to 1.5mm and it＇s impossible to carry out the start-up and thermal fastening.There is risk of flue gas leakage around the flange.These may affect the safe and stable operation of the flue gas turbine.This paper analyzes the weld cracking and flange deformation from such aspects as pipeline layout,metal material,welding process and operating conditions.It is discovered that high temperature creep,intergranular cracking,deteriorating weld toughness and ductility and too large preload occur easily around the weld junction.These are the causesfor the failure.The paper then puts forward corresponding suggestions for improvement in the light of the cause analysis.

The male rotor fracture occurred during the starting process of screw compressor in the oil product unit of certain refinery.This paper makes an analysis on the macroscopic examination,chemical composition,metallographic examination,hardness testing and operating conditions of the fractured male rotor.The results show that the heat treatment of the male rotor didn＇t meet the design requirements.Because of abrasion,Laser cladding was carried out on the surface before the fracture of the male rotor and cracking appeared on the Laser cladding layers.During operation,the cracking expanded and led to fatigue fracture of the male rotor.According to the fracture causes,the paper puts forward the corresponding suggestions for improvement.

This paper introduces the main configuration form and basic parameters of the main air blower set and the actual operating parameters of the flue gas turbine in a Qingdao refinery adopting MIP-CGP process in catalytic cracking unit.It makes an in-depth analysis on the steam overrun of flue gas turbine disc cooling.The paper discovered the root causes for the change of steam parameters.During the device operation,the influencing factors for disc cooling steam are verified by way of setting modification methods such as changing the steam temperature under the premise of ensuring the safety.Then,the final technological revamp scheme is presented.

The oxidation dryer in a PTA plant of certain petrochemical company has run for threeyears.In the production process,the inner buildup of the dryer＇s cylinder frequently occurs and the scaling is formed,resulting in feed opening blockage and short-term running.This not only affects the longterm operation,but also brings safety risks.This paper analyzes the causes for the scaling problems within the dryer and takes corresponding measures to reduce the number of alkaline wash,which saves the cost of maintenance and energy consumption and helps to achieve the goal of extending the dryer＇s cycle of operation.

The styrene exhaust gas compressor was taken down because of the high vibration of its gearbox.After many overhauls,the fault was still not eliminated.By using the online state monitoring system-system 1,this paper makes an analysis on the vibration spectrum from four aspects including unbalanced force,even unbalance,dynamic unbalance and assembly size.According to the vibration characteristic reflected by the vibration axis locus diagram,the dynamic unbalance is finally diagnosed as the cause for the high vibration and the interlocking of the gearbox.The maintenance plan is formulated again at site.After online and offline dynamic imbalance elimination,the fault is resolved and styrene exhaust gas compressor runs well.

A performance test platform for cryogenic submersible pump used in LNG filling station is developed in cryogenic liquid nitrogen environment.The platform is composed of calibration system,pipe system,control system and hoisting system.It can test the performance parameters of the lift,flow and efficiency of cryogenic submersible pump.After the submersible pump is installed in the test platform,the system can realize the pre-cooling,start-up and frequency change of the pump.It can record the operating data automatically as well.Through testing on a cryogenic submersible pump of certain type,the flow-efficiency curve and flow-lift curve are ob-tained.The results show that the test platform could test the performance parameters of LNG cryogenic submersible pump effectively.

Homemade experimental apparatus is adopted to simulate the CO_2 corrosion of all kinds of steels at plug flow.The effects of different steels on CO_2 corrosion are studied by analyzing the coupon surface morphology,corrosion rate through electronic microscope and corrosion coupon.The results show that the resistance to uniform corrosion of 304 stainless steel is obviously higher than those of A333,X65 and X70steel;the resistance to uniform corrosion of stainless steel 304 changes little in a wide range of corrosion conditions;the corrosion rate appears larger fluctuation along with the change of corrosion conditions of A333,X65 and X70;there is a little difference in the uniform corrosion rate among the steel types of A333,X65 and X70.

This paper briefly introduces the influence of target torque,target bolt load and elasticinteraction of bolts on flange sealing performance.It clarifies that the proper method for flange joints has great effect on the reliability of sealing performance and construction efficiency.Then the Japanese standard,JIS B 2251—2008：Bolt Tightening Procedure for Pressure Boundary Flanged Joint Assembly is introduced.Combining with ASME PCC-1—2013and previous research achievements,the paper introduces and analyzes the application scope,setting the value of target tightening torque,precautions,loading process,targeted preload acquisition rate and derivation method of the standard.It summarizes that this standard is worth spreading due to its high construction efficiency and low bolt preload discrete degree.

Aiming at the flow instability of additives in the operation of solid additive system of extruding and pelletizing unit in polypropylene plant,this paper found out the causes for the problem through analysis and verification of the process control and the additive characteristics of the system.Then it put forward corresponding improvement measures which eliminated the unstable factors of the solid additive system effectively and solved the interference of large amplitude of additive flow fluctuation to the product quality.Meanwhile,these also ensured the longterm stable operation of the system.