CONSTRUCTION CODE FOR BOILERS
|Notification No.197 of the Ministry of Health, Labour, and Welfare
Article 42. Scope
Part 1. Steel Boilers
Chapter 3. Workmanship and Hydraulic Tests
Section 1. Welding
Welding of those boiler parts which are subject to exposure to pressure shall be made in accordance with the prescriptions hereunder in this section except when such parts are not liable to any stress other than compressive one.
Article 43. Welding Method
1.Welding shall be made in such a way that the weld zones have necessary strength for safety.
2. Welding of any of those boiler parts which are liable to significant bending stress shall be avoided.
Article 44. Holes in Weld zones
1. No hole may be made in any weld zone (including all parts within 6 mm from the edges of the weld metal). However, this does not apply to those weld zones which have been given post weld heat treatment and have passed the radiographic examination.
2. The radiographic examination referred to in the proviso of the preceding paragraph shall cover an area extending over at least 1.5 times the diameter of the tube hole from the center of such hole in both ways.
Article 45. Efficiency of Welded Joints
1. The allowable tensile stress of weld zones shall be the value that is obtained multiplying the figures specified in the Article 3 or the Article 4 by the efficiency of the welded joint.
2. The efficiency of any welded joint in the preceding paragraph shall be equal to the appropriate one of the values specified in the right column of the following table according to the type of welded joints listed in the left column thereof:
|Type of welded joint
||Efficiency of welded joint (%)
|For joints subject to radiographic examination
||For joints not subject to radiographic examination
|(1) Double-welded butt joint or the single-welded butt joint (the latter process being available only if it is performed with a backing strip or some other method to ensure sufficient penetration: this also applies to the following items.) with the backing removed after welding
|(2) Single-welded butt joint with the backing retained in place after welding
|(3) Single-welded butt joint other than the preceding two items
|(4) Double full fillet welded lap joint
|(5) Single full fillet welded lap joint
Article 46. Post weld Heat Treatment
1. All weld zones shall be subject to post weld heat treatment. However, this provision does not apply to weld zones which do not require any post weld heat treatment such as seal weldings.
2. The post weld heat treatment shall be performed in furnace satisfying the requirements in JIS Z3700 (Methods of Post Weld Heat Treatment Procedures) or standards that can be recognized as equivalent (hereinafter referred to as "the JIS etc. in this paragraph). However, for such weld zones as circumferential joints in shells, headers, tubes, etc. for which a local heating method is considered to be possible, the post weld heat treatment may be done by a local heating method. In these cases, the holding temperature and holding time prescribed in the JIS etc. may be reduced only if the performance of post weld heat treatment at the specified holding temperature and time is hardly feasible or otherwise unsuitable because of such factors as the need for site welding, the materials used or structural restraints.
3. In the case where use of a special material and/or a special structure or some other factors make it difficult or unsuitable to perform post weld heat treatment by either of the methods specified in the preceding paragraph, such treatment may be made by the method prescribed elsewhere by the Director-General of the Prefectural Labour Bureau.
Article 47. Requirements for Weld Zones
All weld zones shall have sufficient penetration and shall be free of such defects as cracks, undercuts, overlaps, craters, slag inclusion, blowholes, etc. that are harmful.
Article 48. Mechanical Tests for Weld Zones
All weld zones shall be subject to the mechanical tests prescribed in the Articles 51 through 54 herein on test plates prepared under the following items and shall meet the requirements.
(1) For the welding of any longitudinal joint in a shell, one test plate shall be prepared for the whole shell by simultaneously welding the test plate and the longitudinal joint with the former attached to the end of the shell in such a manner that its weld line will be on the same straight line as the longitudinal joint. However, if longitudinal joints in all sections of the shell are not welded under identical conditions, one test plate shall be prepared for each section of the shell.
(2) For the welding of any circumferential joint in a shell or of the joint of a dome or some other component, one test plate shall be prepared for the whole shell separately from the shell, dome or the other boiler component by welding the test plate immediately after the joint of such boiler component under the same conditions as for the latter (however, this provision does not apply if the test plate specified in the preceding item is welded under the same conditions as the circumferential joint of the shell or the joint for attachment of the dome or some other boiler components and is subjected to the mechanical tests under Articles 51 through 54 herein).
(3) For the welding of headers or some other boiler components which are used in substantial quantities, one test plate shall be prepared for every 60 meters of the longitudinal weld line and a fraction thereof, provided that the components in a set do not vary any more than 6 mm in plate thickness or any more than 150 mm in diameter and that all of such components are made of the same material and are welded one immediately after another under the same conditions.
Article 49. Test Plates
1. Test plates shall confirm to the same classification of the base metal specified in JIS standards, or any standard that is recognized as equivalent, and be made from the material with same thickness as base metal and be protected from warp resulting from welding.
2. Any test plate, if warped by welding, shall be straightened before it undergoes post weld heat treatment.
3. Test plates shall receive the same post weld heat treatment as the weld zones of the boiler component to be examined.
Article 50. Types of Mechanical Tests etc.
1. The types of mechanical tests applicable to each thickness category of test plate shall be one of the followings:
(1) For test plates less than 19 mm in thickness: tension test, face bend test and root bend test;
(2) For test plates not less than 19 mm in thickness: tension test, root bend test (which may be replaced by a face bend test if the test plate is double-butt welded) and side bend test.
2. Test pieces to be subjected to a mechanical test shall be taken from the test plate in the way described in the Appendix 11 of JIS B8265 (Construction of Pressure Vessels -- General Principles) or any standard that is recognized as equivalent, and one such test piece shall be prepared for each type of mechanical test to be conducted.
Article 51. Tension Test
1. The method of any tension test and the shape and size of tension test pieces shall be as prescribed in JIS Z3121 (Method of Tension Test for Butt Welded Joint) or any standard that is recognized as equivalent.
2. Notwithstanding the provision in the preceding paragraph, any test piece which is too thick to be subjected to a tension test may be cut with a thin saw into slices of proper thickness for such test. In this case, all slices of the test piece shall be found by the tension test to come up to the applicable standards.
Article 52. Acceptance Criteria for Tension Test
1. In a tension test, the test piece shall be deemed acceptable if it is found to have a tensile strength not lower than the minimum tensile strength at room temperature for the base metal.
2. If a test piece breaks at any part of its base metal during the tension test referred to in the preceding paragraph, such test piece may be deemed acceptable, provided that the tensile strength recorded at the time of breaking is not less than 95% of the minimum tensile strength at room temperature specified for the base metal under the applicable standards and that the weld zone of the test piece is free of any defect.
3. If a test piece is rejected by the tension test mentioned in paragraph 1 because of any defect in the base metal, the tension test may be nullified.
Article 53. Bending Tests
1. The shapes and sizes of test pieces for face bend, root bend and side bend tests, and their methods and jigs used for the said tests shall be in compliance with JIS Z3122 (Method of Guide Bend Test for Butt Welded Joint) or any standard that is recognized as equivalent.
2. The provisions in the paragraph 2 of the Article 51 herein apply to the bending tests.
Article 54. Acceptance Criteria for Bending Tests
In the bend tests, test pieces shall be deemed acceptable if they are found free from any crack exceeding 3 mm in length (not including minor cracks appearing at the edge corners) on the outside of their weld zones.
Article 55. Eligibility Requirements for Retests
When the results of the mechanical tests prescribed in the Article 52 or the preceding Article were unsatisfactory, retest may be conducted if the results fall under one of the followings:
(1) In the case of a tension test, the recorded results come up to at least 90% of the specified standards;
(2) In the case of a bend test, the rejection of the test piece is found attributable to a defect other than any in its weld zone.
Article 56. Test Pieces and Acceptance Criteria for Retests
1. A retest shall be conducted on two new test pieces prepared for each of the rejected test pieces from the same test plate that was used for the rejected test pieces or another test plate that was prepared at the same time as such used test plate, and these new test pieces shall be deemed acceptable if they are found by the mechanical retest to meet the requirements under the Article 52 or 54.
2. If the test plate is not large enough to make the new test pieces mentioned in the preceding paragraph, an additional test plate may be prepared by the same boiler welder who made the test plate from which the rejected test pieces were taken and under the same conditions as such used test plate was prepared.
Article 57. Radiographic Examination
Longitudinal joints, circumferential joints, etc. of the shell or the head plate shall be subject to radiographic examination over their whole length and shall be found by such examination to meet the requirements under the Article 59. However, such radiographic examination may be omitted in each of the following items:
1. The circumferential joint in the shell the longitudinal joint of which has passed the radiographic examination, and which has been welded by the same boiler welder who made the longitudinal joints and by the same method as used for the longitudinal joint; or
2. Those recognized by the Director-General of Prefectural Labour Bureau that the radiographic examination to be unnecessary.
Article 58. Height of Reinforcement of Weld
1. The reinforcement of weld for those joints which are subject to radiographic examination shall be such that does not interfere with the said examination.
2. Single welded butt joints using backings are allowed to subject to radiographic examination with the backings retained in place unless they interfere with such examination.
Article 59. Methods and Acceptance Criteria for Radiographic Examination
The methods and the results of radiographic examination shall be conducted in accordance with the applicable one of the following items, depending on the class of base metal:
1. Steel (excluding stainless steel): The examination shall be conducted in accordance with JIS Z3104 (Methods of Radiographic Examination for Welded Joints in Steel), and the defects of the Grade 1 through the Grade 4 shall be the Class 1 or the Class 2 of the classification by the image on radiograph specified in the said JIS standard, or the examination shall be conducted in accordance with other method that is recognized as equivalent to JIS Z3104 and the equivalent results shall be obtained.
2. Stainless steel: The examination shall be conducted in accordance with JIS Z3106 (Methods of Radiographic Examination for Welded Joints in Stainless Steel), and the defects of the Grade 1 through the Grade 4 shall be the Class 1 or the Class 2 of the classification by the image on radiograph specified in the said JIS standard, or the examination shall be conducted in accordance with other method that is recognized as equivalent to the standard JIS Z3106 and the equivalent results shall be obtained.
Article 60. Radiographic Reexamination
If any weld assembly fails in a radiographic examination to meet the requirements under the preceding Article, the defective part because of which the assembly has been rejected shall be completely removed and rewelded, and then such reweld zone shall be subjected to another radiographic examination in which it shall be found to meet the requirements in the preceding Article. The proviso in the Article 57 does not apply to such reexamination.
Article 61. Hydraulic Tests
Section 2. Hydraulic Tests
1. Any of the boilers subject to the standards herein shall be found free of any defect by a hydraulic test under the pressure 1.5 times the maximum allowable working pressure (except when the test pressure thus determined is lower than 0.2 MPa in which case 0.2 MPa apply).
2. Notwithstanding the provisions in the preceding paragraph above, those hot water boilers which are not subject to exposure to pressure above the maximum allowable working pressure shall be found free of any defect by a hydraulic test under pressure 0.1MPa higher than the maximum allowable working pressure (except when the test pressure thus determined is lower than 0.2 MPa in which case 0.2 MPa apply).
3. The boiler parts specified in the following items shall be found free of any defect by a hydraulic test under the appropriate one of the pressure levels prescribed in these items. If any of the parts under the item (1) is to have any opening in it, such part shall be subjected to a hydraulic test before the opening is made in it, and if the test pressure given in the item is lower than the level determined under the preceding paragraph, the test shall be conducted under the pressure prescribed in that paragraph.
(1) Welded parts of water tube boilers: 1.5 times the maximum allowable working pressure
(2) Parts of iron casting: double the maximum allowable working pressure
4. The hydraulic test in the item 1 of the preceding paragraph may be omitted if radiographic examination or ultrasonic examination of weld zones can be conducted after the fabrication of the boiler and if the repairing of weld zones is possible.