Vietnam Standard
TCVN 6008 - 1995 Pressure equipment Welds Technical requirements and control method
Preamble The Standard TCVN 6008-1995 replaces for Chapter V- Examination on weld of QPVN 23-81, Part V- Examination on weld and Part VI-Hydraulic testing of QPVN2 – 75. The The Stan Standa dard rd TCVN TCVN 6008 6008-1 -199 995 5 is comp compil iled ed by Divi Divisi sion on of Tech Techni nica call Stan Standa dard rd TCVN TCVN/T /TC C 11 Pres Pressu sure re Equi Equipm pmen ent, t, sugg sugges este ted d by Gene Genera rall Department of Standard – Measurement – Quality and issued by Department of Science, Technology and Environment
Vietnam Standard Pressure equipment Welds Technical requirements and control method This standard stipulate technical requirements about welding, heat treatment, control method on welds of pressure equipment This standard is not applied to brazing and soldering. 1. Gene Genera rall req requi uirem remen ents ts 1.1 Allowed to use all kinds of welding methods such as: oxy-acetylene oxy-acetylene welding, electric arc welding, electro slag welding, gas metal arc welding, etc to weld pressured parts of equipment. Weldi Welding ng proc process ess,, meth method od of exam examina inatio tion n shall shall be stipu stipulat lated ed in the techn technica icall documents of designing organization. 1.2 Only welders with certified qualification qualification for hydraulic equipment welding welding are allowed to weld the pressured parts of pressure equipment. 1.3 Each welder is allowed allowed to only perform the works stated in the qualification qualification records. records.
1.4 Weld the parts of pressure equipment equipment only after checking checking and ensure that fabrication fabrication and assembling meet the technical requirements. 1.5 Tack welding welding rod and welding rod shall be made of the same material. 2. Tech Techni nical cal requi requirem remen ents ts 2.1 Before welding, welding, the edge of welds and the surrounding metal parts shall be cleaned until seeing shining light. The minimum cleaned width is 10mm from each side. 2.2 The slag of previous pass shall shall be removed before welding welding the next pass.
2.3 If the surrounding temperature is lower than 0 oC, any pressured parts shall not be welded for fabrication no matter what kind of steel it is made of and with any depth.
2.4 When When butt welding welding carbon steel pipes of differen differentt diameter diameter,, allow allow to expand the small pipes but not exceeding 3% of internal diameter if the small pipe diameter is up to 83mm and its thickness is up to 6mm 2.5 Allow automatic automatic and manual welding welding on the same weld. Automatic weld, which is added by shield arc metal welding not exceeding 15% of horizontal weld joint, is still regarded as an automatic weld. 2.6 Welding technology technology shall ensure ensure that stress in the welds do not exceed the permitted permitted value. 2.7 Coefficient Coefficient of resistance resistance of electric arc welding, oxyacetylene oxyacetylene welding is stipulated by designing organization but shall not be greater than the value stated in the table 1 Table 1
Wel Welding ing tec techn hno olog logy an and me metho thod
Coeffi effic cient ient of res resiistanc tance e of of we weld
1. Manu Manual al wel weldi ding ng
-
Single butt weld without backing
0.70
-
Single butt weld with backing
0.90
-
Double butt weld
0.95
2. Auto Automa mati tic c weld weldin ing g
-
Single butt weld without backing
0.80
-
Double butt weld
1.00
2.8 Weld Weld shall shall be: a. On externa externall examining examining and and measurin measuring, g, without without:: -Crack on the weld surface and fusion metal parts; -Knob, notch, burnt hole, incomplete fusion and other defects; -Curve, misalignment; -Different in size and shape of the weld as well as reinforcement b. On metalog metalograph raphic ic testing testing:: -Without crack in the melted metal as well as areas of basic metal which is thermally affected; -Without incomplete fusion between passes and edge;
-Without incomplete incomplete penetration in the weld root exceeding 15% of the wall thickness thickness or over 3mm if the wall thickness is over 20mm for the products to be single welded; -Without gas pore and slug inclusion exceeding 5stains/cm 2, the size of each defect do not exceed 1.5mm and not over 3mm in total; -Without fracture in the composition which reduce resiliency and flexibility of metal. c. On hydra hydraul ulic ic testi testing ng -No fracture on the weld; -No water leakage; -No visible deformation 2.9 The result result of the tensile tensile test, test, calculated calculated by average average sum sum of the test test samples, samples, should should not be lower than minimum durability of equivalent calculation, in which no sample is lower than 10% of the minimum durability. 2.10 The result of the bend test shall not be lower than numeric value value stated in the table 2. For those parts are made of other materials excluding from the table 2, value of the bend angle shall be stipulated by the designing organization Table 2
Kinds of steel
Carbon steel Alloy steel with low mangan and
Permitted Bending angle (radius) Electrical welding, resistance Oxy-acetylene welding, electro slag welding if welding if the wall the thickness of welded parts thickness not (mm) exceeding 12mm Up to 20 Over 20 100 100 70 80
60
50
molybdenum and chrome-
50
40
30
molybdenum -vanadium Alloy steel with high chrome Alloy steel with high chrome-
50
40
30
100
100
30
silic-mangan Alloy steel with low chrome-
molybdenum
2.11The resistance numeric value against strike of the weld metal shall not be lower than the stipulated numeric value in the table 3
Environment temperature on test, oC 20 Lower than 0
Table 3 The smallest Resistance value against strike of the weld For all kinds of steel except For austenite steel austenite steel 49.05 68.67 19.62 29.43
2.12 Heat treatment treatment for weld a. The bellow bellow case case shall shall pass heat heat treatment treatment after after weldin welding g -Welding alloy steel with thickness from 10mm upwards -Welding carbon steel with 0.27% of carbon in volume with 35mm upwards in thickness -Whe -When n weld welding ing carb carbon on steel steel with with over over 0.27 0.27% % carbo carbon n regar regardle dless ss of thick thickne ness, ss, the the designer shall stipulate. b. Regu Regulat lation ion of heat heat treatm treatmen entt and and metho method d of heat treatm treatment ent are stipu stipulat lated ed by the designer c. Heat Heat treatment treatment is allowed allowed for each weld weld separatel separately y or with pressured pressured parts, parts, but heat heat treatment shall be done before checking the weld quality. 3. Chec Checkin king g the the quali quality ty of weld weld 3.1 3.1
General ral re require irements nts
3.1.1 3.1.1 Manufac Manufacture turer, r, assembler assembler,, repairer repairer shall check check the quality quality of weld done done by them for the pressured parts. 3.1.2 The quality quality of weld weld shall be be checked by one, some some or all all of the following following methods, depending on type of welds and working specifications of equipment -External examination, applied to all kinds of welds. -Detect defects by ultrasonic testing or radiographic testing. -Destructive testing, metalographic testing. -Hydraulic testing, applied to all kinds of welds. 3.1.3 Beside methods specified specified in article article 3.1.2, 3.1.2, welds welds must be examined examined by by other methods if regulated by manufacturing technical requirements. 3.2
Surface test
3.2.1 3.2.1 Surfa Surface ce test and measur measurem ement ent shall shall be made made on two two sides sides of weld weld’s ’s length. length. When it is impossible to examined inside surface, only outside surface is enough.
3.2.2 3.2.2 Weld’ Weld’s s surfa surface ce and meta metall close closed d two two sides sides of weld weld must be clean cleaned ed before before examining. It required to be cleaned with 20mm in width. 3.3
Destructive te test
3.3.1 Destructive Destructive test test shall be done done to check check weld’s weld’s durability durability and and endurance. endurance. Destructive test must includes: Tensile test, Bend test (for pile, press test can be taken instead of bend test) Impact test, 3.3.2 3.3.2 Beside Beside three kinds kinds of test mentioned mentioned in article article 3.3.1, 3.3.1, depending depending on requireme requirements nts on manufacturing, technique and operating, other destructive tests may be added such as hardness test, charpy notch test 3.3.3 Tensile test must must be taken according according to Vietnamese Vietnamese Standard Standard TCVN 5403-1991 5403-1991.. It is not compulsory to taken tensile test for horizontal weld, which was 100%, examined by ultrasonic test. 3.3.4 3.3.4 Bend Bend test test (pres (press s test) test) must be taken taken accord according ing to requir requirem emen entt of Vietn Vietnam ames ese e standard TCVN 5401-1991. Pressure bend test can replace for pipe with diameter lower than 100mm and the edge’s thickness lower than 12mm. 3.3.5 Impact test must must be taken according according to Vietnamese Vietnamese Standard TCVN 5402-1991. 5402-1991. 3.3.6 3.3.6 Test Test piec piece’s e’s dimens dimension ion for for destr destruct uctive ive test is in accord accordanc ance e with with Viet Vietnam names ese e Standard TCVN 5400-1991. 3.3.7 Quantity Quantity of welds welds for test in comparison comparison with with same kind kind welds welds of one welder welder is: 1% for carbon steel or low alloy steel. 2% for austenite alloy steel but not less than one weld joint for each welder. 3.3.8 Dimension Dimension of patch, patch, pipe for test must must be enough enough for cutting cutting required required test test pieces. 3.3.9 3.3.9 From From weld or test piece piece shou should ld be taken: taken: 02 tensile test pieces 02 bend test pieces (or press test) 03 impact test pieces 3.3.10 Weld product product and weld in plate (pipe) for test must be done by one welder in the same conditions. 3.3.11 Weld test piece (product) (product) will not be accepted if with any kind of test, one result showing figure on bend angle and durability is above 10% lower than regulated figure 3.3.12 When result of any kind of test does not meet the requirement, requirement, the second test should be done at that kind of test with doubled number of test samples from one plate (or pipe) examined by the old welder.
3.3.13 Welding Welding Sample (product) shall be removed removed if result of one of the second sample is not satisfactory. 3.4
Ultra Ultrason sonic ic testi testing ng and and rad radiog iogra raphi phic c testi testing ng (gam (gamma ma,, X-ray X-ray))
3.4.1 3.4.1 Welds Welds shall be examined examined by Ultrasonic Ultrasonic testing testing and radiograp radiographic hic testing testing to detect the inside defects which cannot be visually recognized. 3.4.2 Ultrasonic Ultrasonic examination examination shall shall be carried carried out according according to requirement requirements s in Standard Standard Vietnam Standard Standard 1548-1987 1548-1987 Non destructive destructive weld weld examination examination – Ultrasonic Ultrasonic method. 3.4. 3.4.3 3 Radi Radiog ogra raph phic ic exam examin inat atio ion n shal shalll be perf perfor orme med d in acco accord rdan ance ce with with Viet Vietna nam m Standard 4395-1986. Non destructive weld examination – Examination of metal welds by X-ray and gamma ray 3.4.4 The quantity quantity of welds examined examined by ultrasonic ultrasonic or radiograp radiographic hic shall shall not be smaller than quantity stated in table 4
Usage and working specifications of equipment
The length ratio need to be checked against total length, or quantity of welds of pipes need to be checked against quantity of weld, %
-Mainten -Maintenance ance,, transpor transportt of explosi explosive ve and high exotic substances
100
-Working -Working with pressure pressure higher than 50at at tem tempera peratu turre high igher tha than 200o 200oC C and and smaller than –70oC
100
-Working with pressure up to 50at and in the temperature temperature limit between between –70oC and and +200oC
50
-Working -Working with pressure pressure up to 16at and wall temperature from –40oC to +200oC
25
3.4. 3.4.5 5 Allo Allowe wed d to redu reduce ce the the quan quanti tity ty exam examin ined ed by ultr ultras ason onic ic and and radi radiog ogra raph phic ic if permitted by steam boiler inspector.
3.4.6 3.4.6 The The result result of ultra ultrason sonic ic weld weld exam examina inati tion on is evalu evaluate ated d accor accordin ding g to Stand Standard ard Vietnam Standard 1548-1987; radiographic examination under Vietnam Standard 4395-1986 3.4.7 3.4.7 Allowed Allowed to replace replace the method method of ultrasonic ultrasonic and radiogr radiograph aphic ic defect detect detect by other non destructive method if approved by steam boiler inspector 3.5 Metalographic testing 3.5.1 Metalographic testing shall be done in the following cases: Weld at parts with working temperature higher than 150oC and pressure higher than 40at Welds at parts with working pressure higher than 50at at any temperature Nozzles Nozzles (if ultraso ultrasonic nic testing testing and radiogr radiograph aphic ic testing testing are impossi impossible) ble) with working working pressure higher than 40at. Longitudinal stiffening and stiffening on the pipe. 3.5. 3.5.2 2 Spec Specim imen en quan quanti tity ty:: - Minimum one specimen for carbon steel. - Minimum two specimens for alloy steel. 3.5. 3.5.3 3 The The meth method od of taki taking ng speci specime mens ns,, size size,, and and shap shape e of test test piec pieces es shall shall be in accordance with the technical requirements stipulated in the current standards.
3.5.4 When the result of metalographic testing is not satisfactory, there shall be the second test on 2 specimens from the product weld. The weld is considered as unsatisfactory if the 2 nd testing do not meet requirement. 3.5.5 Those welds which meet requirement requirement on on ultrasonic ultrasonic testing or radiograph radiographic ic testing testing but but the the meta metalo logr grap aphi hic c test testin ing g is not not sati satisf sfac acto tory ry,, 100% 100% of weld welds s shal shalll be examined by the non-destructive methods already used. 3.6
Hydraulic te test
3.6.1 3.6.1 The welds welds of pressure pressured d parts of pressure pressure equipm equipment ent shall shall be hydraulic hydraulic tested tested by water or other liquids of equivalent characteristics.
3.6.2 Pressure of hydraulic testing must be in accordance with the value in the table 5. 5. 3.6.3 3.6.3 The durat duration ion of maint maintaini aining ng at test test pressur pressure e is 5 minutes. minutes.
Equipment
Working pressure P, Kg/cm2
Testing pressure, Kg/cm2
Contain taine er (exce xcept cas cast container), steam boiler
P up to 5
2P but not smaller than 2kg/cm2
Contain taine er (exce xcept cas cast container), steam boiler
P over 5
1.5P bu but no not sm smaller th than 10kg/cm2
Heat exchanger (1)
(1)
According to testing pres press sure calcu lculat lation ion of steam boiler
Water Warmer (2)
(2)
According to testing pres press sure calcu lculat lation ion of steam boiler
Not depe depen nding ding on press ressur ure e
2P but but not not smal smalle lerr tha than 3kg/cm2
‘’
1.5P but not smaller than 3kg/cm2
Conn Connec ecti ting ng pipe pipes, s, heat heat receiving pipes when testing each pipe Cast container
(1) Pressure Pressure P is working pressure of steam boiler when when go out of the heat exchanger. (2) Closed water water warmer: Pressure Pressure P is working pressure of the water warmer. warmer. Unclosed water warmer: Pressure P is working pressure of the steam boiler.
