mud pump broken bolts made in china

A 1-off fastener was designed by a sub-unit of the company, based on a existing Inconel 718 bolt design... without consulting him first. A very reputable fastener company made a prototype run (~100) per the drawing. The production run was very economical and timely... however, ALL of the bolts failed to inspect/perform as anticipated [stabilizer attachment bolt with altered head design]. Tensile/shear strength, Fatigue, etc... where way-low based on the altered existing design. Everyone was upset and livid that a reputable company would make such trash. WHY... There were even "odd dimensional and NDI defects" in a couple of the parts. OUTRAGEOUS!!!!

My favorite personal example is socket head cap screws. we were using the heads inside a countersink to hold alignment in a machine we had just built. the heads were within spec (barely) but the heads were not on the same centerline as the bolts. So needless to say the bolts would not fit. I spent the day chucking bolts into the lathe and shaving the heads till they were concentric because we couldn"t wait for new ones.

Lastly the 8 countersunk holes were all round, and all fit fine with better quality bolts, we just did not have enough of them on hand and expected when we ordered more that we would get a similar product.

To start, I don"t bolt cylinder heads or exhaust manifolds, indeed, ANY engine part, with surplus or G8. Critical engine hardware is reserved for ARP, SPS... custom fasteners. I do use G8 and in some cases, NAS surplus in other mounting areas...safety straps for drive shafts, camber plates, roll bar trunnions, mounting plates for accessories, accumulators, fuel pumps and filters...that sort of thing. Nothing critically loaded.

A circulating water pump is a key equipment of cooling systems in nuclear power plants. Several anchor bolts were broken at the inlet rings of the same type of pumps. The bolts were turned by a special material for seawater corrosion protection. There were obvious turning tool marks at the root of the thread, which was considered as the source of the crack. The fatigue crack extended to the depth of the bolt, causing obvious radiation stripes on the fracture surface, which was a typical fatigue fracture. Obvious overtightening characteristics were found at the head of the broken bolt. Fracture and energy spectrum analysis showed that the bolt was not corroded. The axial vibration of the pump was measured. The static tensile stress along the bolt axis caused by the preload, the axial tensile stress caused by the axial vibration, and the torsional stress were calculated, respectively. According to the fatigue strength theory, the composite safety factor of the bolt fatigue strength was 1.37 when overtightening at 1.2 times the design torque, which was less than the allowable safety factor of 1.5-1.8, so the bolt was not safe, which further verified the conclusion of fracture analysis. The reason for the low safety factor was caused by the overtightening force. The improvement method was to control the bolt preload or increasing the bolt diameter.

A cooling water pump is a very important equipment in nuclear power plants. During overhaul, it was found that the fixing bolts of the embedded parts of four CR1QS1 pumps were broken. The pump is a single-stage, vertical, bottom-suction concrete volute centrifugal pump. The pumps were fixed on the concrete embedded parts with 8 hexagon socket bolts through the mouth ring, as shown in Figure 1. The purpose of the protective cap is to protect the bolt from erosion. The working medium of the pump is sea water.

The common failure modes of bolt fracture are fatigue fracture, stress corrosion cracking, and overload fracture. Due to the large stress concentration of a bolt thread, it is easy for a fatigue source to form at the root, and the possibility of fatigue fracture is high. The bolt fracture studied by González et al. occurred at the second turn of the screw thread, which was caused by hydrogen embrittlement [1]. The bolt studied by Shafiei and Kazempour-Liaisi had M23C6 carbide, which was the source of the fatigue crack. The crack propagates along the grain boundary, and finally, fatigue fracture occurs [2]. Li et al. found that surface decarburization of the bolts and stress concentration at the bolt thread neck decreased the fatigue strength [3]. Wu et al. studied the corrosion fracture mechanism of cable bolts [4]. The fracture had general fatigue fracture characteristics. There were corrosion fatigue crack sources and radial fatigue crack propagation traces. Hydrogen-assisted stress corrosion cracking was the main fracture mechanism of cable bolts failure. The fatigue crack source of the bolt-sphere joint was pitting caused by corrosion [5]. Wen et al. [6] studied the fracture of a 20MnTiB steel high-strength bolt. Microdefects were found near the bottom of the thread. Considerable stress and corrosion accelerated the crack propagation of the bolt. The working capacity of a rock bolt decreased by 25-50% when it worked under the condition of rock and groundwater corrosion [7].

It is generally believed that the fatigue strength of bolts is only related to the stress amplitude. The fatigue strength only studied the stress amplitude of bolt tensile stress [7–10]. For example, the bolt fatigue strength condition was that the allowable stress amplitude was equal to 90 MPa [8], and the fatigue curve studied was the curve [9]. However, in practice, many examples showed that the failure of bolts was related to the average stress (i.e., bolt preload) [11, 12]. The reason for a bolt fracture was that the safety factor is insufficient due to excessive preload [11, 12]. The safety factor of static strength is obtained by preloading, the safety factor of variable stress is obtained by strain, and the safety factor is modified by Goodman’s theory [13].

In this paper, the fracture analysis, mechanical property analysis, and energy spectrum analysis of the broken bolt are carried out. At the same time, the fatigue strength of the bolt is calculated, the failure causes are found out, and the improvement suggestions are put forward. Finally, the calculation method of the bolt fatigue strength is proposed.

The bolts in service are shown in Figure 2, in which Nos. 1 and 2 were the unbroken bolts, Nos. 3-6 were the head of the broken bolts, and Nos. 7-11 were the rest of the broken parts of the broken bolts. Compared with the spares, their surfaces were the same as the serviced bolts, indicating that there was no corrosion.

The fracture of No. 3 bolt in Figure 2 is representative. Take it as an example to illustrate the fracture form of bolts. Figures 3(a) and 3(b) are the overall morphology and local morphology of the No. 3 bolt, respectively. There are obvious radial lines on the edge of the thread teeth, which is the fracture source as the point indicated by the arrow. The fracture source extends to the core, and then the bolt breaks when the crackle reaches the middle. This is the instantaneous fracture zone region, where the section is rough and uneven. The instantaneous breaking zone occupies a relatively large area, indicating that there is a large residual pretightening force when the bolt is broken.

Figure 5(a) is the morphology of the inner hexagon of the head of No. 3 broken bolt. The top of the bolt head is damaged when the sample was taken on site, as shown by the arrow. But the inner hexagon area is damaged during tightening, as shown in the region. Figure 5(b) shows the morphology of the unbroken bolt head, with the inner hexagon of the screw head intact. The comparison shows that the broken bolts have overtightening behavior when they were installed.

Figure 7 shows the macroimages of four unbroken screws through dye penetrant inspection, and no cracks are found on the surface. The metallographic structures of the unbroken and broken bolts are, respectively, shown in Figures 8(a) and 8(b), which show an austenite + ferrite structure. This conforms to the characteristics of dual phase steel, without obvious abnormality.

The bolts were made of a special material for seawater corrosion protection. Due to the small quantity, they were manufactured by turning. The chemical composition meets the ASTM s32760 standard, see Table 1. Using the XHB-3000 Digital Brinell Hardness Tester, the average hardness of bolts is 230-240 HBW, equivalent to grade 8.8 (Chinese national standard GB3098.1), which also meets the requirements of ASTM s32760 of less than 310 HBW.

By the AG100KNG universal testing machine, the tensile properties of sample bolts were tested, as shown in Table 3. The results all meet the requirements of standard values, and the mechanical properties are normal. According to the empirical formula recommended in the mechanical design manual, the symmetrical cycle fatigue limit and torque yield limit are estimated as follows:

Table 4 shows the composition of the fracture surface after cleaning by Energy Disperse Spectroscopy (EDS). The result is the same as the previous conclusion in Section 2.1, that is, as can be seen in Figure 2, the broken bolts were as glossy as the spare parts, and there was obviously no corrosion.

The bolts should be tightened when they are installed; that is, they are subject to the preload (tension) and friction torque. When working, it may be subjected to the variable stress of axial tension. In this paper, the finite element method is used to calculate the tensile stress and torsional stress by ANSYS Workbench 15.0 software.

The pump and the foundation ring are connected by 8 bolts. The finite element model takes 1 bolt and one eighth of the foundation including the ring and concrete, as shown in Figure 9. According to the equipment maintenance manual, the installation torque of the bolt is 40.5 Nm, the torque coefficient is 0.258, and the calculated preload is 13081 N.

The axial tensile stress and torsional stress of the bolt are shown in Figures 10 and 11, respectively. The axial tensile stress is 434.05 MPa, and the torsional stress is 59.29 MPa at design torque. If the overtightening torque reaches 1.2 times the design value, the axial tensile stress is 520.86 MPa, and the torsional stress is 71.41 MPa. The inner hexagon of the broken bolt head has been seriously damaged, and the actual torque is far greater than 1.2 times the design value.

When the pump runs, the impeller will have a working load, acting on the bolt axis direction. The stress is a symmetrical cyclic strain produced by the axial vibration when the pump is running. The axial load was obtained by actual measurement. A speed sensor was installed at the bearing, and the excitation spectrum load was the relationship between the speed and the frequency spectrum, as shown in Figure 12.

(1)There are obvious crack sources at the root of the thread, and there is an obvious fatigue fracture zone and an instantaneous fracture zone at the cross section. The fatigue fracture zone is typically radial and has typical fatigue fracture characteristics(2)The bolt safety factor at 1.2 times the design torque is 1.37, which has been less than the allowable safety factor of 1.5-1.8. Therefore, the fatigue strength of bolts is insufficient, and a bolt fracture is due to fatigue failure when the bolt is overtightened(3)The failure of bolts is not caused by seawater corrosion. The surface of the broken bolt is bright, and there is no trace of corrosion(4)The key cause of a bolt fracture is too much preload. The measure to improve the safety factor is to control the bolt preload or increase the diameter of the bolt

A circulating water pump is a key equipment of cooling systems in nuclear power plants. Several anchor bolts were broken at the inlet rings of the same type of pumps. The bolts were turned by a special material for seawater corrosion protection. There were obvious turning tool marks at the root of the thread, which was considered as the source of the crack. The fatigue crack extended to the depth of the bolt, causing obvious radiation stripes on the fracture surface, which was a typical fatigue fracture. Obvious overtightening characteristics were found at the head of the broken bolt. Fracture and energy spectrum analysis showed that the bolt was not corroded. The axial vibration of the pump was measured. The static tensile stress along the bolt axis caused by the preload, the axial tensile stress caused by the axial vibration, and the torsional stress were calculated, respectively. According to the fatigue strength theory, the composite safety factor of the bolt fatigue strength was 1.37 when overtightening at 1.2 times the design torque, which was less than the allowable safety factor of 1.5-1.8, so the bolt was not safe, which further verified the conclusion of fracture analysis. The reason for the low safety factor was caused by the overtightening force. The improvement method was to control the bolt preload or increasing the bolt diameter.

A cooling water pump is a very important equipment in nuclear power plants. During overhaul, it was found that the fixing bolts of the embedded parts of four CR1QS1 pumps were broken. The pump is a single-stage, vertical, bottom-suction concrete volute centrifugal pump. The pumps were fixed on the concrete embedded parts with 8 hexagon socket bolts through the mouth ring, as shown in Figure 1. The purpose of the protective cap is to protect the bolt from erosion. The working medium of the pump is sea water.

The common failure modes of bolt fracture are fatigue fracture, stress corrosion cracking, and overload fracture. Due to the large stress concentration of a bolt thread, it is easy for a fatigue source to form at the root, and the possibility of fatigue fracture is high. The bolt fracture studied by González et al. occurred at the second turn of the screw thread, which was caused by hydrogen embrittlement [1]. The bolt studied by Shafiei and Kazempour-Liaisi had M23C6 carbide, which was the source of the fatigue crack. The crack propagates along the grain boundary, and finally, fatigue fracture occurs [2]. Li et al. found that surface decarburization of the bolts and stress concentration at the bolt thread neck decreased the fatigue strength [3]. Wu et al. studied the corrosion fracture mechanism of cable bolts [4]. The fracture had general fatigue fracture characteristics. There were corrosion fatigue crack sources and radial fatigue crack propagation traces. Hydrogen-assisted stress corrosion cracking was the main fracture mechanism of cable bolts failure. The fatigue crack source of the bolt-sphere joint was pitting caused by corrosion [5]. Wen et al. [6] studied the fracture of a 20MnTiB steel high-strength bolt. Microdefects were found near the bottom of the thread. Considerable stress and corrosion accelerated the crack propagation of the bolt. The working capacity of a rock bolt decreased by 25-50% when it worked under the condition of rock and groundwater corrosion [7].

It is generally believed that the fatigue strength of bolts is only related to the stress amplitude. The fatigue strength only studied the stress amplitude of bolt tensile stress [7–10]. For example, the bolt fatigue strength condition was that the allowable stress amplitude was equal to 90 MPa [8], and the fatigue curve studied was the curve [9]. However, in practice, many examples showed that the failure of bolts was related to the average stress (i.e., bolt preload) [11, 12]. The reason for a bolt fracture was that the safety factor is insufficient due to excessive preload [11, 12]. The safety factor of static strength is obtained by preloading, the safety factor of variable stress is obtained by strain, and the safety factor is modified by Goodman’s theory [13].

In this paper, the fracture analysis, mechanical property analysis, and energy spectrum analysis of the broken bolt are carried out. At the same time, the fatigue strength of the bolt is calculated, the failure causes are found out, and the improvement suggestions are put forward. Finally, the calculation method of the bolt fatigue strength is proposed.

The bolts in service are shown in Figure 2, in which Nos. 1 and 2 were the unbroken bolts, Nos. 3-6 were the head of the broken bolts, and Nos. 7-11 were the rest of the broken parts of the broken bolts. Compared with the spares, their surfaces were the same as the serviced bolts, indicating that there was no corrosion.

The fracture of No. 3 bolt in Figure 2 is representative. Take it as an example to illustrate the fracture form of bolts. Figures 3(a) and 3(b) are the overall morphology and local morphology of the No. 3 bolt, respectively. There are obvious radial lines on the edge of the thread teeth, which is the fracture source as the point indicated by the arrow. The fracture source extends to the core, and then the bolt breaks when the crackle reaches the middle. This is the instantaneous fracture zone region, where the section is rough and uneven. The instantaneous breaking zone occupies a relatively large area, indicating that there is a large residual pretightening force when the bolt is broken.

Figure 5(a) is the morphology of the inner hexagon of the head of No. 3 broken bolt. The top of the bolt head is damaged when the sample was taken on site, as shown by the arrow. But the inner hexagon area is damaged during tightening, as shown in the region. Figure 5(b) shows the morphology of the unbroken bolt head, with the inner hexagon of the screw head intact. The comparison shows that the broken bolts have overtightening behavior when they were installed.

Figure 7 shows the macroimages of four unbroken screws through dye penetrant inspection, and no cracks are found on the surface. The metallographic structures of the unbroken and broken bolts are, respectively, shown in Figures 8(a) and 8(b), which show an austenite + ferrite structure. This conforms to the characteristics of dual phase steel, without obvious abnormality.

The bolts were made of a special material for seawater corrosion protection. Due to the small quantity, they were manufactured by turning. The chemical composition meets the ASTM s32760 standard, see Table 1. Using the XHB-3000 Digital Brinell Hardness Tester, the average hardness of bolts is 230-240 HBW, equivalent to grade 8.8 (Chinese national standard GB3098.1), which also meets the requirements of ASTM s32760 of less than 310 HBW.

By the AG100KNG universal testing machine, the tensile properties of sample bolts were tested, as shown in Table 3. The results all meet the requirements of standard values, and the mechanical properties are normal. According to the empirical formula recommended in the mechanical design manual, the symmetrical cycle fatigue limit and torque yield limit are estimated as follows:

Table 4 shows the composition of the fracture surface after cleaning by Energy Disperse Spectroscopy (EDS). The result is the same as the previous conclusion in Section 2.1, that is, as can be seen in Figure 2, the broken bolts were as glossy as the spare parts, and there was obviously no corrosion.

The bolts should be tightened when they are installed; that is, they are subject to the preload (tension) and friction torque. When working, it may be subjected to the variable stress of axial tension. In this paper, the finite element method is used to calculate the tensile stress and torsional stress by ANSYS Workbench 15.0 software.

The pump and the foundation ring are connected by 8 bolts. The finite element model takes 1 bolt and one eighth of the foundation including the ring and concrete, as shown in Figure 9. According to the equipment maintenance manual, the installation torque of the bolt is 40.5 Nm, the torque coefficient is 0.258, and the calculated preload is 13081 N.

The axial tensile stress and torsional stress of the bolt are shown in Figures 10 and 11, respectively. The axial tensile stress is 434.05 MPa, and the torsional stress is 59.29 MPa at design torque. If the overtightening torque reaches 1.2 times the design value, the axial tensile stress is 520.86 MPa, and the torsional stress is 71.41 MPa. The inner hexagon of the broken bolt head has been seriously damaged, and the actual torque is far greater than 1.2 times the design value.

When the pump runs, the impeller will have a working load, acting on the bolt axis direction. The stress is a symmetrical cyclic strain produced by the axial vibration when the pump is running. The axial load was obtained by actual measurement. A speed sensor was installed at the bearing, and the excitation spectrum load was the relationship between the speed and the frequency spectrum, as shown in Figure 12.

(1)There are obvious crack sources at the root of the thread, and there is an obvious fatigue fracture zone and an instantaneous fracture zone at the cross section. The fatigue fracture zone is typically radial and has typical fatigue fracture characteristics(2)The bolt safety factor at 1.2 times the design torque is 1.37, which has been less than the allowable safety factor of 1.5-1.8. Therefore, the fatigue strength of bolts is insufficient, and a bolt fracture is due to fatigue failure when the bolt is overtightened(3)The failure of bolts is not caused by seawater corrosion. The surface of the broken bolt is bright, and there is no trace of corrosion(4)The key cause of a bolt fracture is too much preload. The measure to improve the safety factor is to control the bolt preload or increase the diameter of the bolt

The pump casing and pump cover are welded by steel plates. The bearing seat of the transmission shaft and the crankshaft is an integral steel casting, which is welded with the pump casing after processing, and annealed after welding to eliminate residual stress. The dimensions of the overhanging parts at both ends of the drive shaft of mud pump parts are completely symmetrical, and large pulleys or sprockets can be installed at both ends. The supporting bearings at both ends adopt single row radial short cylindrical roller bearings.

The crankshaft adopts a forged straight shaft eccentric wheel structure, which replaces the traditional integral cast crankshaft structure of the three-cylinder pump. The casting is changed to a forging, and the whole is changed to an assembly. It is easy to use, easy to manufacture, and easy to maintain. The eccentric wheel, herringbone gear hub and shaft adopt interference fit. The small end of the connecting rod of the mud pump parts is equipped with a pin shaft, and the two ends of the pin shaft are equipped with single-row radial short cylindrical roller bearings, which are assembled on the crosshead. The body of the crosshead is made of ductile iron, and the guide plate is made of ductile iron. The crosshead and the middle rod are connected by flanges and bolts.

The integral forging is a vertical structure, and it is a series of drilling pumps with the smallest clearance volume among high-power mud pumps. The mud pump spare parts valve box is discharged and sucked through the discharge manifold and the suction manifold, one end of the exhaust manifold is equipped with a high-pressure four-way and exhaust pre-compression air bag, and the other end is equipped with a lever type (single-pin multi-point) shear safety valve. The discharged pre-compressed air bag is an integral casting, its body, capsule and sealing ring, and the inflation pressure of the pre-compressed air bag capsule is 20%-30% of the working pressure.

According to user requirements, a special electric centrifugal pump or a centrifugal pump driven by a drive shaft is used as a spray pump, and the cylinder liner is cooled and lubricated through the nozzles on the spray box. Generally, water or water-based solution (soluble emulsified oil or diesel oil can be added) is used as the cooling liquid, which flows into the water tank for recycling.

The overall forged assembly and welding structure are adopted, the discharge manifold of the mud pump parts and the front planes of the three valve boxes are connected by bolts and sealed with O-shaped packing, and the discharge valve chambers do not communicate with each other.

My fellow-7-owner had been looking over the engine in a moment of dry calm on an otherwise wet Driver Education Day at Blackhawk Farms. His sharp eye had found what I hoped was just a vibration-assisted backed-off bolt. But a few twists made it clear that the threads were simply not catching, and the bolt was free in its passage through a margin of the water pump (which was not leaking any vital fluids... a degree of relief to be savored).

With the aid of my mates, the water pump pulley was soon detached, and the offending bolt almost fell into my hand... sheared just into the threads! That meant that the majority of the threads were still lodged firmly in the block!

Despite the absence of any leakage around the water pump, efforts focused on replacing the bolt shaft, as it was apparent that it was essential! Not to keep the water pump in place, but to continue to provide the mandatory tension to the Alternator belt. The Alternator Stay originates on this bolt, and without it, no electrics! The resultant tension must have been the force that caused the fracture in the first place, as the Alternator Stay contacts this bolt near its head, some 3cm off the block where the security of thread-on-thread contact ends. The combined forces of this tension and the vibrations of the four-cylinder Cross-flow Ford engine on a 16 lb-ft torqued bolt over time must have conspired to break the steel shaft through the unopposed threads some time in the last 6,000 miles since the engine rebuild!

Perhaps the genius that is FORD had failed this particular bolt, but the water-pump pulley brilliantly kept even this fractured bolt from backing ALL the way out, as the head of the bolt came into contact with the back side of the pulley if it backed out a centimeter, keeping the shaft safely within the bore of the water pump passage, and thus able to continue to hold the Alternator Stay in its assigned position. Clearly, it had explored this freedom, as the pulley surface was smoothly polished of paint, and that of the head of the bolt also sanded smooth by their mutual contact from time to time! The assembled Corps minds, however, believed that this movement should be minimized, so a few zip ties around a motor mount soon constrained the bolt nearer its home burrow!

A few laps at speed revealed that the bolt remained in position, if not tight, and provided the Alternator Stay adequate tension to provide charge while in motion, and that the water pump continued to remain sealed to the block without any leakage. Safe enough to drive home to Willowbrook!

I had hopes of accomplishing this without removing the water-pump, but decided it was wise to just remove it completely to allow direct access to the broken bolt. This allowed a well-centered punch to be applied without the guesswork trying to do so through the 3cm, blind aperture provided by the water pump housing. Of course, it means dealing with most of the antifreeze volume, and having to clean up the gasket surfaces and cutting a new gasket for eventual replacement of the water pump, but if it’s worth doing, it may be worth doing it correctly!

I replaced the damaged bolt with a newly purchased Grade 8 unit, in hopes I could avoid a similar fate with the design given in this Ford set-up. I cleaned those threads in the block with a few passes of the new bolt until I was certain it too would not seize in place. (I added copper anti-seize on final assembly for good measure!) A new gasket, cut and glued in place with 3M material, should assure return to drip-free water -pump function for the foreseeable future. I then simply re-torqued the bolt pattern to spec, thanks to the folks at Pegasus who included this data in their catalog on the Ford Cross-flow page (it’s a great resource for an engine that remains plentiful and apparently in wide-spread use, lo these many years!), refilled the coolant capacity and reset the proper Alternator Belt tension.

The newly replaced Alternator Stay Bolt, and its securely attached Water Pump, remain in their appointed places, even with another 2,000 miles since this little repair. The Great Minnesota Lotus Corps Tour was great, and without any mechanical detraction this time around, for me and the little Westfield Sei, including its sturdy Cross-Flow Ford! Many miles of smiles seem likely with the aid of a little ingenuity and properly applied technology. I hope your project has equal fortunes if you, too, run into a broken bolt in due course!

Rural families that sold a large agricultural surplus to the market not only could afford to buy more charcoal, tea, oil, and wine, but they could also amass enough funds to establish secondary means of production for generating more wealth.Suzhou often specialized in raising silk wares, while in Fujian, Sichuan, and Guangdong farmers often grew sugarcane.wheelwrights mass-producing standardized waterwheels and square-pallet chain pumps that could lift water from lower planes to higher irrigation planes.

Kaifeng shopkeepers rarely had time to eat at home, so they chose to go out and eat at a variety of places such as restaurants, temples, and food stalls.Restaurant businesses thrived on this new clientele,precious paintings, as well as shops selling bolts of silk and cloth, jewelry of pearls, jade, rhinoceros horn, gold and silver, hair ornaments, combs, caps, scarves, and aromatic incense thrived in the marketplaces.

According to government regulations concerning seagoing ships, the larger ones can carry several hundred men, and the smaller ones may have more than a hundred men on board. One of the most important merchants is chosen to be Leader (Gang Shou), another is Deputy Leader (Fu Gang Shou), and a third is Business Manager (Za Shi). The Superintendent of Merchant Shipping gives them an unofficially sealed red certificate permitting them to use the light bamboo for punishing their company when necessary. Should anyone die at sea, his property becomes forfeit to the government...The ship"s pilots are acquainted with the configuration of the coasts; at night they steer by the stars, and in the day-time by the sun. In dark weather they look at the south-pointing needle (i.e. the magnetic compass). They also use a line a hundred feet long with a hook at the end which they let down to take samples of mud from the sea-bottom; by its (appearance and) smell they can determine their whereabouts.

Considerable scholarship has been concentrated on researching the level of living standards during the Song dynasty. A recent study by economic historian Cheng Minsheng estimated the average income for lower-class laborers during the Song dynasty as 100 wen a day, about 5 times the estimated subsistence level of 20 wen a day and a very high level for preindustrial economies. Per capita consumption of grain and silk respectively was estimated by Cheng to be around 8 jin (about 400 g each) a day and 2 bolts a year, respectively.

The root of the development of the banknote goes back to the earlier Tang dynasty (618–907), when the government outlawed the use of bolts of silk as currency, which increased the use of copper coinage as money.Tianbao period of 742–755, and only 220 million coins minted annually from 118 BC to 5 AD during the Han dynasty).