Material and Allowable Stress
Article 8. Material of Steel Penstocks
Materials used for steel penstocks shall be those listed in Table 1.8-1. Materials other than those in Table 1.8-1 may be used provided that a sufficient study be made.
Table 1.8-1 Types of Materials
1. Rolled steel for general structure |
JIS G 3101 (1976) |
2. Rolled Steels for welded structure |
JIS G 3106 (1977) |
3. Hot-rqlled atmospheric corrosion resisting steels for welded itructure |
JIS G 3114 (1977) |
4. Steel plates for pressure vessels for intermediate temperature service |
JIS G 3115 (1977) |
5."Steel bars for rivet |
JIS G 3104 (1976) |
6. Carbon steel castings |
JIS G 5101 (1978) |
7. Steel castings for welded structures • |
JIS G 5102 (1978) |
8. Carbon steel forgings for general use |
JIS G 3201 (1977) |
9. Gray iron castings |
JIS G 5501 (1976) |
Description:
This standard is specified to use the material whose characteristics are
clear, and it is necessary to confirm that the material meets the requirements of the JIS standard by material tests before fabrication. But when the material characteristics concerned are clear enough with the material test records made by its steel manufacturer. the records can be a substitute for material tests. The material tests in tliis Article should include tests not only for strength but also for whether or not the dimension (thickness, etc.) is within the tolerance.
Tolerances for plate thicknesses should.be in accordance with the standard specified in Article 9., this Chapter.
It is a special case to use JIS materials other than those in Table 1.8-1 or materials other than JIS, and careful consideration should be given to this case.
For instance, in case that such standard pipes as Carbon Steel Pipes for Pressure Service (JIS G 3454), Arc Welded Carbon Steel Pipes (JIS G 3457), etc., are employed as a steel penstock material in such locations as small-scaled hydraulic power stations, a careful study and review should be made to their material, manufacturing methods, inspection methods,
e. the adaptability to a steel penstock, and each paragraph of this standard should be applied to their use.
Article 9. Material of Pressure Lining Part and Main Attachment Installations Directly Welded to Pressure Lining Part 1. Materials used for pressure lining parts and main attachment installations directly welded to the former shall be the kind listed hereunder or steel material having equivalent or superior characteristics.
(JIS
G3101 SS41)
(JIS
G3106 SM41-SM50-SM50Y-SM53-SM58)
(JIS
G3114 SMA41-SMA50-SMA58)
Steel
Plates for Pressure Vessels for (JIS G3115 SPV24-SPV32-SPV36-SPV46)
Intermediate Temperature Service .
!
2.
Tolerances for the thickness of pipe shell plates used for pressure
lining parts monarticular
can be specified separately.
Description :
The pressure lining part is the most important portion in a steel penstock, and so the material used for this should be in accordance with this Article, and should be economical as well as safe.
“Main attachment installations ^directly welded_to ,^he^pressure lining part” include stiffeners, ring girders, manhole'remforcem'ents, etc., and for these, steel material having equivalent or superior characteristics to the pressure lining part should be used because the above installations work structurally together with the pressure lining part.
“Steel material having the equivalent or superior characteristics” may include high tensile steels other than those in JIS (See Article 11., this Chapter).
With the same material, the notch toughness gets poorer as the thickness increases, and the material is likely to be br i ttl^f ractur ed depending, on the notch condition, temperatures, rate of loading, etc. Therefore, steels having a better notch toughness should be used as the thickness increases.' In case of more than 12mm thick plates, it is preferred to use a plate having a shock-absorbing energy of more than 2.8kgf.m (0°C).
For steel materials thicker than 25mm, it is necessary to use killed steel or semi-killed steel up to strength of SM50, and killed steel for more than strength of SM 50Y. SM 50Y is semi-killed steel added usually with niobium, on the other hand SM53 and SM58 are killed steel so SM53 should * be used as a substitute for a plate thicker than 25mm.
As for thickness tolerances for pipe shell plates used for the pressure lining part in particular, the minus side may be restricted. The minus side of the thickness tolerance is frequently restricted to — 0.25mm in conformity with the steel plate standards used for boilers and pressure vessels, JIS G31O3, and JIS G3115.
Article 10. Material of Attachment Installations
Steel material shall be used for attachment installations which are not directly welded to the pressure lining part and which are closely related to the pressure lining part.
Description:
Attachment installations which are closely related to the pressure lining’part are expansion joints, manholes, air pipes, air valves, supporting structures, etc., and since these are directly concerned with the safety of
'■’V -tewle -xik
the pressure lining part, steel material (steel casting inclusive), not iron casting, are required to be used for the portions subjected to loads even if these portions are not directly welded to the pressure lining part.
Article 11. Material Test
Testing, inspection and marking of materials other than those in Table 1.8-1, Article 8. of this Chapter shall be.in accordance with General Rules for Inspection of Steel (JIS G0303), unless otherwise specified in each standard for respective material.
2 .When attempting to use particularly thick plates or special materials, weldability and other matters of the materials concerned shall be tested.
Description:
1 . When using materials other than those in Table 1.8-1, it is necessary to make sure that the materials conform to the JIS standard if they are based on JIS, if the materials are not based on JIS it is necessary to make sure of the acceptable results required by inspection and testing in accordance with “General Rules for Inspection of Steel.”
When attempting to use especially thick plates or special materials, some . problems in terms of manufacture such as workability, weldability and
others mayarise, and thus it is specified that, in addition to the general tests included in “General Rules for Inspection of Steel,” problematic points should be tested.
For each steel material, tests other than those specified in JIS are as -■follows: .
Parent material .... workability test, heat affecting test, heat treatment test, brittleness test
Weld Zone hardness test, crack test, joint strength test, brit
tleness test
Weld material useability
There are anti-corrosive test, structure test and others provided for special materials.
Testing example for steel penstocks is listed in Table 1.11-1.
‘ u
•-"Pr-A - 73 -
Power station |
Morozuka j |
Okutataragi |
||
Used steel plate thickness (mm) |
4T60 2-20 |
Steel forging equivalent to SM58Q©' Section 300 x 480 290 x 560 |
||
1 Type or test |
’arent material |
Workability |
|
|
Heat affection and heat treatment |
|
•Hardness lest (steel plate & steel forging) |
||
Low temperature brittleness |
|
•Temp, gradient type ESSO test (steel plate) •NRL drop weight test (steel plate) |
||
Weld zone |
Hardness |
. oint hardness |
•Joint hardness (steel plate &. steel forging) |
|
Crack |
•Kommerell bead bend test, Kinzel test© |
•Bead bend test (steel pl.) •Y-groove cracking test (steel pl.) •Deep notch test (steel pl.) , ■» •Diffusible hydrogen quantity & cracking ratio (steel pl.) |
||
Mechanical property |
•Joint tension test •Joint bending test •Joint fatigue test |
•Joint tension test (steel pl. & steel forging) •Joint impact test (steel pl. & steel forging) •Joint bending test (steel forging) |
||
4* Weldin materials |
Useability |
•Tension test of deposited metal |
•Full size automatic welding procedure test (steel pl.) •Full size hand welding procedure lest • , (steel pl) •Automatic and hand welding test with full size thick plates (forged steel, joint) |
|
Others |
|
•Investigation of stress relief annealing effect (steel pl. & forged steel) |
||
Structure |
|
•Internal pressure destructive test |
* |
|
Year of completion |
1960 |
1975 |
||
Remarks |
Reason for additional test |
60kgf/mm2 class high tensile steel to be used for the first lime for steel penstock |
60kgf/mmJ class high tensile steel with extreme thickness to be used |
|
Note |
©Additionally, Y-groove cracking test & tension test for double lee type fillet welded joint for reference |
@ Carbon equivalent g0.44 Tensile strength 58-73kgf/mm2 Yield point ^44kgf/mm2 vE_j . i4.8kgf-m ©'Carbon equivalent 50.50 Tensile strength 58~73kgf/mm2 Yield point 44kgf/mm2 vE j >3.5kgf-m |
||
Tabic 1.11-1 Example of Special Additional Test (cont’d)
Power station |
Shimotaki |
Numappara |
Ohhira |
||
Used steel plate thickness (mm) |
HT70© 24 - 29 |
HT70© 22 - 34 |
HT80© 32 - 36 |
||
i |
|
Workability |
•Linear heating angular distortion lest |
•Strain aging impact test |
•Strain aging impact test |
1 |
1 Parent 1 material | i |
Heat affection and heat treatment |
•Taper hardness test •Preparation for welding CCT diagram |
•Taper hardness test •Max. hardness test • Preparation for welding CCT diagram •Thermal cycle test |
•Taper hardness test •Thermal cycle test •Max. hardness test •Preparation for welding CCT diagram |
I 1 i |
j i |
Low temperature brittleness |
•ESSO test •Drop weight test |
•Double tension test •Deep notch test •NRL drop weight test |
•Deep notch test |
• |
|
Hardness |
•Joint hardness |
•Joint hardness |
•Joint hardness |
i Type of test |
- Wdd zone |
Crack |
|
•Bead bend test •Y-groove cracking lest •Diffusible hydrogen quantity & cracking ratio |
•Bead bend lest •Y-groove cracking test •Window type restraint weld cracking test •Diffusible hydrogen quantity & cracking ratio |
|
i— |
Mechanical property |
•Joint tension test •Joint impact test |
•Joint tension test •Joint impact lest •Joint fatigue lest |
•Joint tension lest •Joint impact lest •Joint fatigue lest |
|
Welding materials |
Useability |
•Automatic welding procedure lest ® •Full size welding procedure lest |
•Automatic welding procedure test •Hand welding procedure test |
•Automatic welding procedure test •Hand welding procedure lest |
|
Others |
|
•Investigation of stress relief annealing effect |
•Investigation of stress relief annealing effect |
|
Year of c |
Structure ompletion |
i |
1963 |
•Wide tension test with angular folding 1972 |
•Wide tension test with angular j folding 1975 |
|
Reason for additional test i i i |
70kgf/mm2 class high tensile steel to be used for-lhe first time for steel penstocks |
70kgf/mm2 class high tensile steel with extreme thickness to be used for the first time for steel penstocks |
80kgf/mm2 class high tensile steel to be used for ihe first lime for steel penstocks |
|
Remarks |
1 Note 1 1 1 1 i 1 |
|
©Material to be in conformity with WES SH 66 Tensile strength 74kgf/mm2 Yield point 66kgf/mm2 Elongation 25°7o ®CO2 + UM system |
©Carbon equivalent §0.49 Tensile strength g70kgf/mm2 Yield point S63kgf/mm2 vTrs 2 -35 °C (parent material) I vTrs § -O’C . (welded joint) |
©Carbon equivalent §0.53 Tensile strength 1 i80kgf/mm* Yield point g70kgf/mm2 vE.^g 3.6kgf-m (parent material) vEg g 3.6kgf-m (welded joint) |
■ ... .... , ;■
Table 1.11-1 Example of Special Additional Test (cont’d)
Power station |
Okukiyoisu |
|||
Used steel thickness (mm) |
HT80 steel plate i = 3- - : j, 75 © Steel forging equivalent :? HT80 section 260 x 525, 270x450 ® HT80 + SUS 304L clad steel plate t = 34 + 3, 39 + 3 ® |
|||
Type of lest |
Parent material |
Workability |
Strain aging impact test steel plate) |
|
Heat affection and heat treatment |
'aper hardness test (steel pl.) vlax. hardness test (steel pl.) Strength and toughness test after SR (steel pl.) Tempering test (steel pl.) |
|||
Low temperature brittleness |
)eep notch lest (steel pl.) ’'cmp. gradient type ESSO test (steel pl.) NRL drop weight test (steel pl.) |
|||
Weld' zone |
Hardness |
. oint hardness (every max. thickness for all combinations of steel materials and welding processes) |
||
Crack |
Y-groove cracking test (every max. thickness for all combinations of steel materials and welding processes) Window type restrain weld cracking test (every max. thickness for all combinations of steel materials and welding processes) Cracking test for fillet welded joint (t = 75 steel plate, covered arc welding) . •» Cracking test for boundary layer (t = 39 + 3 clad, steel plate, covered arc welding) Deep notch test (t = 50, 75 steel pl. weld zone) |
|||
Mechanical property |
Joint tension test (all welded joints having max. pl. thickness in every combination of steel pl. and welding process) Joint impact test (all welded joints having max. pl. thickness in every combination of steel pl. and welding process) Joint fatigue test (for t = 50 steel pl. butt welded joint, covered arc welding, submerged arc welding, MIG semi-automatic welding) Offset joint fatigue test (for t = 35 steel pl., MiG automatic butt welded joint) |
|||
Welding material |
Useability |
Automatic MIG welding procedure test (full size model) Semi-automatic MIG welding procedure test Submerged arc welding procedure test Covered arc welding procedure test |
||
Others |
|
|||
Structure |
|
Wide tension test for cross-shaped joint with angular distortion (t = 75 steel pl. & steel forging) (for investigation of low temperature brittleness) |
||
Year of completion |
1977 |
|||
Remarks |
Reason for additional test |
80kgf/mm2 class high tensile steel with extreme thickness to be u$ed for steel penstocks |
||
Note |
t 5 50mm 51 < t s 100mm ©Carbon equivalent g 0.53 g 0.57 Tensile strength 80~95kgf/mm2 78-93kgf/mm2 Yield point Je 70kgf/mm2 £ 68kgf/mm2 vTrE (parent material) -40°C < -40°C vE.^o (parent material) > 3.6kgf-m . £ 3.6kgf-m vTrE (weld zone) < 0°C < 0°C . vE0 (weld zone) i 3.6kgf-m > 3.6kgf-m |
|||
Power
station
Note
Remarks
surface
2: 68kgf/mm2
... — • <1
surface
k -40°C
r
surface 2: 3.6kgf-m • core part 4.8kgf-m ::
o.6o . : : ''
80 - 95kgf/ mm2 ,
\
a
lOkgf/mm1
s
—20°C
(parent
material) SO’C (weld tone)
_
. i 3.6kgf-m (parent material) 2: 3.6kgf-m (weld zone)
Okukiyotsu
©Carbon equivalent g 0.60 . - core part
Tensile strength surface 78 ~93kgf/mm2-. 76 ~93kgf/rnm2 - Yield point surface 2: 68kgf/mm2 —core part 65kgf/mml • vTrc ' ~ .
VE_^ vE_, ~ "
©Carbon equivalent
Tensile strength
Yield point
vTrB
vTrE
vE_w L L
Power station |
Okuyoshino |
||
Used steel thickness (mm) |
T80 steel plate t = 34- 50, 59, 60, 78 ® Steel forging equivalent to HT80 section 350 x 680, 350 x 525 ® |
||
Type of lest |
Parent material |
Workability |
Strain aging impact test (steel plate) |
-leal affection and heat treatment |
Taper hardness lest (steel pl. & steel forging) Tempering test (steel pl. & steel forging) SR brittleness lest (steel pl.) Thermal cycle lest (steel forging) Short bead cracking lest (steel pl.) |
||
_Z)W temperature brittleness |
Deep notch lest (steel pi.) ; Double tension test (steel pl.) Two point bending COD test (steel pl.) |
||
Weld zone |
-iardness |
, oint hardness (every max. thickness for all combinations of steel materials and welding processes) |
|
Crack |
Y-groove cracking test (every max. thickness for all combinations of steel materials and welding processes) Window type restraint weld cracking lest (every max. thickness , or all combinations of steel materials and welding processes) Cracking test for T-type fillet welded joint (t = 78 steel pl., covered arc welding) Cracking'test for restraint lap joint (t = 50 steel pL, covered arc welding) ■ _ Deep notch test (t = 50 steel pl. weld zone) |
||
Mechanical property |
Joint tension test (all welded joints having max. pl. thickness in every combination of steel pl, & welding process) Joint impact test (all welded, joints having max. pl. thickness in every combination of steel pl. & welding process) Joint fatigue test (l = 50 steel pl. and steel forging butt joints welded with covered arc, submerged arc and semi-automatic MIG welding) Offset joint fatigue test (t = 35 steel pl. butt joints by automatic MIG welding) |
||
Welding materials |
Useability |
Automatic MIG welding procedure lest (full-size model) Semi-automatic MIG welding procedure test Submerged arc welding procedure lest (full-size model) Covered arc welding procedure lest (full-size model) |
|
Others |
Weld metal strain aging test (each butt welding material used, for automatic MIG, semi-automatic MIG, submerged arc, covered arc welding) Weld metal SR brittleness test (each butt weld material used for automatic MIG, semi-automatic MIG, submerged arc, covered arc welding) |
||
Structure . |
|
Wide tension test for cross-shaped joint with angular distortion (t=78 steel pl. &'stcel forging) (for investigation of low temperature brittleness) Three point bending COD lest (t = 50, 78 steel pl. weld zone) |
|
Power station |
■ • - — — - |
Okuyoshino |
|
Year of completion |
1980 |
||
|
Reason for additional test |
80kgf/mm2 class high tensile steel with extreme thickness to be used for steel penstocks ~~—— |
|
" Remarks |
Note |
©Carbon equivalent • Tensile strength Yield point vTrs (parent material) VE-40 (parent material) vTrs (weld zone) vEo (weld zone) ©Carbon equivalent Tensile strength . Yield point vTrs vE 4o |
t i 50mm 50 < t S 78mm 0.47 ~ 0.53 0.50 - 0.56 80 - 95kgf/mm2 78 - 93kgf/mm2 £ 70kgf/mm2 S 68kgf/mm2
2: 3.6kgf-m 2: 3.6kgf-m
2: 3.6kgf-m 0.57 ± 0.03 78 - 93kgf/mm2 2: 68kgf/mm2 1 -40’C 2: 3.6kgf-m |
Power station |
Nabara |
|||
Used steel thickness (mm) |
HT80 t = 27 - 32 Steel pl. © ■ test piece l = 34) |
|||
Type of Lest |
Parent material t |
Workability |
Strain aging impact test |
|
Heat affection and heat treatment |
Taper hardness test vlax. hardness test Thermal cycle test Tempering test Re-heating test |
|||
Low temperature brittleness |
Deep notch test |
|||
Welded .part |
Hardness |
Joint hardness test (covered arc, submerged arc welding) |
||
Crack |
Window type-restraint weld cracking test (submerged arc welding) Y-groove cracking test (covered arc welding) |
|||
Mechanical property |
Joint tension test (covered arc, submerged arc welding) Joint bending test (covered arc, submerged arc welding) Joint impact test (covered arc, submerged arc welding) t Joint with reinforcement tension test (submerged arc welding) ’ Weld metal tension test (submerged arc welding) . |
|||
Weld material |
Useability |
Field welding procedure test (covered arc welding) Y-groove cracking lest Window type restraint weld cracking test |
||
Others |
Measurement of cooling speed of submerged arc welding |
|||
Structure |
|
|
||
Year of completion |
1976 |
|||
Remarks |
Reason for additional test |
80kgf/mm2 class high tensile steel to be used for steel penstock |
||
Note |
©Carbon equivalent £ 0.53 Tensile strength i80kgf/mm2 Yield point £70kgf/mn? |
|||
Power station |
Okuyahagi No.2 - |
|||
zUsed steel thickness (mm) |
HT80 t = 100 Steel pl. |
Steel forging equivalent to HT80 t = 345 ® |
||
Type of test |
Parent material |
Workability |
|
|
Heat affection and heat treatment |
Taper hardness test |
Taper hardness test Max. hardness test Thermal cycle test Tempering test |
||
Low temperature brittleness |
|
|
||
Weld zone |
Hardness |
Joint hardness test ’submerged arc, MIG welding) |
Joint hardness test (submerged arc, MIG welding steel forging + steel forging t = 345) Joint hardness test (submerged arc, MIG welding steel forging + steel plate t = 100) |
|
Crack |
WOL test, Y-groove cracking test (covered arc welding) |
|||
Mechanical property |
Joint tension test (submerged arc, MIG welding steel forging + steel plate) Joint bending test (submerged arc, MIG welding steel forging + steel plate) Joint impact test (submerged arc, MIG welding steel forging +.. steel plate) Weld metal tension test (submerged arc, MIG welding) |
Joint tension test (submerged arc, MIG welding steel forging + steel forging t = 345) (submerged arc, MIG welding steel forging + steel plate t = 100) Joint bending test (submerged arc, MIG welding steel forging + steel forging t = 345) (submerged arc, MIG welding steel forging + steel plate t = 100) Joint impact test (submerged arc, MIG welding steel forging + steel forging t = 345) (submerged arc, MIG welding steel forging + steel plate t = 100) |
||
Welding materials |
JJseability |
1 |
Automatic welding procedure test (submerged arc, MIG welding) Welding procedure test for steel forging & steel plate(t = 100 submerged arc, MIG welding) |
|
Others |
|
|
||
Structure |
|
|
|
|
Power station |
Okuyahagi No.2 |
||
Year of com |
oletion |
1981 |
|
|
Reason for additional test |
To ensure applicability of HT 80 to steel penstocks |
To review possibility of field weld connection of HT 80 steel forging |
Remarks |
Note |
® Carbon equivalent 0.55 ± 0.01 Tensile strength 78 - 93kgf/mm2 Yield point & 68kgf/mm2 |
® Carbon equivalent 0.59 ± 0.01 Tensile strength g 78kgf/mm2 (core part exclusive) Yield point g 68kgf/mm2 (core part exclusive) |
Article 12. Allowable Stress
Allowable stresses used for design calculation shall be less than those listed in Tabic 1.12-1. As for a joint made of the material concerned, its efficiency shall be taken into consideration. —
Allowable stresses of the materials not specified in Table 1.12-1 shall be decided after taking account of the properties of the materials concerned.
Table 1.12-1 Allowable Stress of Material
Materials |
Tensile ( stress (kgf/ cm2) |
Compressive stress (kgf/ cm2) |
Shearing stress (kgf/ cm2) |
Bearing stress (kgf/ cm2) |
||
Classification |
Kinds |
|||||
Rolled steel for general structure |
SS 41 |
thickness g 40mm thickness > 40 |
1,300 1,200 |
1,300 1,200 |
750 700 |
2,200 2,000 |
Rolled steels for welded |
SM41 |
thickness g 40 |
1,300 |
1,300 |
750 |
2,200 |
structure or Hot-rolled |
SMA41 |
thickness > 40 |
1,200 |
1,200 |
700 |
2,000 |
atmospheric corrosion resisting steels for welded structure |
SM50 ' |
thickness g 40 thickness > 40 |
1,750 1,650 |
1,750 1,650 |
1,000 950 |
3,000 2,800 |
SM50Y |
thickness g 25 |
2,000 |
2,000 |
1,150 |
3,400 |
|
|
SMA50 |
thickness < 40 |
2,000 |
2,000 |
1,150 |
3,400 |
|
SM53 |
thickness > 40 |
1,850 |
1,850 |
1,050 |
3,200 |
|
SM58 |
thickness < 40 |
2,400 |
2,400 |
1,400 |
4,100 |
• |
SMA58 |
thickness > 40 |
2,300 |
2,300 |
1,300 |
3,900 |
Steel plates for pressure ves- |
SPV24 |
thickness g 40 |
1,300 |
1,300 |
750 |
2,200 |
seis for intermediate tempera- lure service |
thickness > 40 |
1,200 |
1,200 |
700 |
2,000 |
|
SPV32 |
thickness g 40 thickness > 40 |
1,750 1,650 |
1,750 1,650 |
1,000 950 |
3,000 2,800 |
|
|
SPV36 |
thickness g 40 thickness > 40 |
2,000 -1,850 |
2,000 1,850 |
1,150 1,050 |
3,400 3,200 |
|
SPV46 |
thickness g 40 thickness > 40 |
2,400 2,300 |
2,400 2,300 |
1,400 1,300 |
4,100 3,900 |
Steel bars for rivet |
SV34 |
|
— |
— |
1,050 |
— |
|
SV4IA |
|
—— |
—- |
1,300 |
— |
Carbon steel castings |
SC42 |
|
700 |
700 |
400 |
1,200 |
SC46 |
|
750 |
750 |
400 |
1,250 |
|
’ f |
SC49 |
|
800 |
800 |
450 |
1,350 |
Steel castings for welded |
SCW42 |
|
1,050 |
1,050 |
600 |
1,750 |
structure |
SCW49 |
|
1,200 |
1,200 |
700 |
2,000 |
Carbon steel forgings for |
SF40 |
|
1,100 |
1,100 |
600 |
1,850 |
general use |
SF45 |
|
1,250 |
1,250 |
700 |
2,100 |
|
SF50 |
|
1,350 |
1,350 |
750 |
2,300 |
|
SF55 |
|
1,550 |
1,550 |
900 |
2,600 |
|
SF60 |
|
1,650 |
1,650 |
950 |
2,800 |
Materials |
Tensile stress (kgf/ cm2) i |
Compressive stress (kgf/ cm2) |
Shearing stress (kgf/ cm2) |
Bearing stress (kgf/ cm2) |
|
Classification |
Kinds |
||||
Gray iron castings |
FC20 |
■ 200 |
200 |
100 |
300 |
|
FC25 |
1 250 |
250 |
150 |
400 |
|
FC30 |
! 300 |
300 |
200 |
500 |
Note: Allowable shearing stresses of rivets and allowable bearing stresses of steel plates in a field riveted joint shall be 80% of the above values.
Description:
Allowable tensile stress [gCL
The allowable tensile stresses of steel materials sp^cifi^d in this Article are decided so that the safety factor should be 1.8 against their basic design strength.
. The basic design strength of a steel material can be obtained by divid- •' jng_the yield point by the material factor. The material factor is the one determined by taking account of differences in the yield ratio, cold workability, absorbing energy up to fracture, and reliability of each steel. Each allowable stress mentioned above is set by taking the material factor of SM58, SPV46 as 1.05, and other steel materials as 1.00.
As for Carbon Steel Castings, they have inferior property in terms ’ of uniform quality, an inspection is hard to be executed, and they
• aje uncertain against impact as a pressure vessel. Thus the safety factor of the steel penstock is taken a| 6 hgainst a tensile strength and even carbon steel castings are treated equally as common steel materials for a hydraulic gate and steel structure.
As for Steel Castings for Welded Structure, the carbon equivalent is specified in JIS, and the shock absorbing energy is also specified • as more than 2.8kgf-m (0 deg. C), and thus the safety factor against the tensile strength is specified as 4.
Carbon Steel Forgings for General Use are specified with the same concept as SS41.
The-safety factor for Gray Iron Castings is specified as 10.
Allowable compressive stress 1 b<3c
According to experiments and so forth, it is said that the compressive strength is almost the same as the tensile strength, and other regulations for steel structures specify the same, and thus this article also follows this conccpL ■ ......
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Allowable shearing stress
The allowable shearing stress is taken as about 1/VTof the allowable tensile stress based on the shearing strain energy fracture theory, and that of SS41 is taken as 750kgf/cm2. As for rivets, it is appropriate to assume that the ratio of allowable shearing stress of shop riveting to the allowable tensile stress of steel material i§ about 80%, and so the stress of SV34 is taken as l ;050kgf/cm2.
Field riveting, compared with shop riveting, is inferior somewhat, and so 80% is set.
Allowable bearing stress
It is generally said that the ratio of a steel plate bearing strength by shop riveting to the tensile strength of a steel plate is about 1.8 to 2.0, and so 170% is taken taking account of an allowance of safety, and the stress of SS41 for instance is taken as 2,200kgf/cm2. Field riveting, compared with shop riveting, is inferior somewhat, and so 80% is set.
Allowable bearing stresses of Gray Iron Castings are also specified with the same concept.
Refer to Article 13., Chapter 4 for joint efficiency.
When using materials not specified in Table 1.12-1 such as HT70, . HT80 etc., the allowable stresses should be decided based on the same
concept of aforementioned material factors. It is appropriate to take 1.15 to 1.20 as the material factor for HT70, HT80 etc.