ESTABLISHMENT OF ULTRASONIC TESTING IN UNIQUE DESIGNED PARTIAL PENETRATION END PLUG OF HEADER IN BOILERS.

Transcription

1 Proceedings of the National Seminar & Exhibition on Non-Destructive Evaluation NDE 2011, December 8-10, 2011 ESTABLISHMENT OF ULTRASONIC TESTING IN UNIQUE DESIGNED PARTIAL PENETRATION END PLUG OF HEADER IN BOILERS. Dharmveer Singh 1 and Abhishek Banerjjee 1 Alstom Projects India Ltd.- Durgapur, WB, End plug is attached at each of the header end. Its design leaves about 3 mm overlap area, which remains un-fused at the root through out the circumference of header, resulting in permanent indications in ultrasonic testing, and hence uncertainty arises about where these indications are coming from. Theoretically no indication should come from the overlap area and indications can come from the interface of weld and parent metal of end plug, providing great difficulty in interpretation if indications are from lack of sidewall fusion or from overlap area. A mock-up block was prepared with sufficient SDHs for simulation of Lack of Side Wall Fusion, MPI and DP was carried for confirmation of overlap area, etching to confirm distinction of weld, HAZ and parent metal, macro was carried out to see the overlap area and then finally UT was carried out and with the simulation it was established that the indications were coming from root indications are coming from the overlap area because of its configuration and such indications should be disregarded. Keywords: End Plug, Overlap, Ultrasonic Testing, Lack of Side Wall Fusion, Side Drill Hole (SDH) INTRODUCTION In the process of manufacturing of a boiler, the one of the most critical component is header which consists of many components, e.g., full penetration nozzles, nipples, butt welds, end plugs etc. Some headers are designed with one end plug while most of the headers with two end plugs at both ends of the header. Headers are designed to endure high pressure, making both the ends of the header pipe body very high pressure bearing area which make sense of end plug welding to be free from any minor defects. By its shape, the most desirable NDE method to detect most possible discontinuities is Ultrasonic Testing whether PA or convention Ultrasonic Testing. The end plug is designed to attaché with header pipe in such a way that it leave 3-5 mm over lap area (Fig 1). Weld deposition is done though the thickness of the end plug, leaving 3-5 mm overlap area un-welded, making this weld not a full penetration weld. When it is examined through ultrasonic, a continuous indication is observed at root or just near root making very difficult to understand the origin of the signals. THEORY Practically those indications should not come from the root overlap area and it gives impression of lack of side wall fusion at the interface of end plug and weld area. It is clear from Fig. 1. that shape suggests that from overlap area there will be no back reflection angle probes ultrasonic Fig. 1 : Schematic diagram of the cross sectional area of header end plug showing the overlap area of 3-4 mm length testing and it ultrasonic testing indicating the signal from root or near root, there are chance to get signals from the lack of side wall fusion which results in rejection. End plug at the end of the over lap area toward pipe cannot be made very sharp corner to have dimensions zero at the edge. There is curved portion left at the edge. At the time of the welding the curved edge portion is welding made its half portion make its melt and no unfused area is left while other half portion toward overlap area kept that curved area as it is. The origin of the signal is most likely to obtained from there. To prove that such indications are from root and not lack of sidewall fusion experimentation was done with mock up block and same welding.

2 NDE 2011, December 8-10, Table : Details of header end plug and header pipe. 3.2 Side Drilled Hole (SDH) Five side drill holes were inserted simulating lack of sidewall fusion and other discontinuities at different locations. Details of locations and depth of these SDHs are given below in Table and in Fig. 3.1 Table : Details of location and depth of SDHs Fig. 2 : Top inside view of the header end plug from which a mock up block is made. EXPERIMENTATION To simulate end plugs a mock up block was prepared of material P 91 (as P 91 being more critical) in such a way that it closely resembles the header end plug welding 3.1 Mock up Block The Mock up block for experimentation was prepared by cutting a cross section from a welding of header eng plug with header pipe. The details of the header end plug and header pipe are enlisted below in Table 3.1 Fig. 3.1 : The cross-sectional view of the mock up block showing the different SDHs. Fig. 3.2 : Mock Up Block with Etching showing the weld configuration. Fig. 3.3 : Liquid Penetrant Test showing overlap area Fig. 3.4 : Liquid Penetrant Test indicating no weld sign when test was done from inner side.

3 196 Dharmveer Singh and Abhishek Banerjjee : Proceedings of the National Seminar & Exhibition on Non-Destructive Evaluation 3.3 Etching To see the exact weld location on the mock up block, etching was carried out as shown in Fig Etching helped to find out exact location of end plug weld to concentrate area of interest. 3.4 Dye Penetrant Testing & Magnetic Particle Testing To make sure about the any surface and near surface discontinuity Magnetic Particle Test was carried out. Dye penetrant testing was carried out over the weld area and from the results of penetrant testing the 3-4 mm overlap area could be clearly identified. Hence both of these tests ensure that the there is a 3-4 mm overlap area at root at the end plug (Fig. 3.3) where there is no sign of weld (Fig 3.4) at the overlap area. For volumetric inspection, ultrasonic testing was done for weld soundness. 3.5 Ultrasonic Scanning Plan: The scanning plan of the mock up block is clearly shown in the Fig.3.5 to insure the complete coverage. As per the plan scanning was done in three ways with normal probe and 45 0 angle probe to cover the entire weld so that no minor defect is left out undetected. The three modes of scanning are as stated below: Normal Probe N-I) N-I ensures the detections of any volumetric discontinuity and longitudinal planer discontinuity along the axis of the header including lack of sidewall fusion at weld-pipe interface as indicated by Fig 3.5. This scanning is done with through out circumferential over the pipe. To make the testing more reliable the testing was carried out with 4 MHz and 2 MHz probe Normal Probe (N-II): N-II Scanning insures volumetric defect detections and planer circumferential (along the circumference of weld) Angle Probe: Scanning was done with 45 0 angle probe from the end plug side ( Probe position : A-III, ref fig 3.31) so that indications from the SDHs and the indication from the overlap area can be differentially identified. Fig. 3.5 : Schematic Diagram of end plug welding and ultrasonic scanning plan. N-I indicates normal probe scanning (2 Frequencies 2 MHz and 4 MHz) from the pipe circumference. N-II indicates normal probe scanning (2 Frequencies 2 MHz and 4 MHz) from the welding side towards the header pipe body. A-III indicates scanning from angle probe (45 0 ) from end plug. RESULT AND DISCUSSION Following result were observed. All five SDHs are detected oriented at different locations.

4 NDE 2011, December 8-10, N-I Scanning No relevant indications were observed while doing scanning with normal probe, all around the circumference indicating no volumetric discontinuity through out weld and no planer defects axial to header pipe. This scanning eliminates the possibility of any lack of sidewall fusion at interface of weld and pipe. N-II Scanning No relevant indications were observed while doing scanning with normal probe, when scanning was carried out at the weld as mentions in figure 3.5 (N-II Scanning). It confirms of the absence of any volumetric discontinuity and any lack of fusion in circumferential direction. A-III Scanning 45 deg was used to scan weld with 4 MHz probe and 2 MHz probe as well. Result of 2 MHz is mentioned below. Side B and Side D, holes were clearly well distinguished with overlap area. Side D was more critical observation. SDH 5 is inserted at end the height of just 2.5 mm above the overlap area and it was well distinguished from the hole.

5 198 Dharmveer Singh and Abhishek Banerjjee : Proceedings of the National Seminar & Exhibition on Non-Destructive Evaluation CONCLUSION 1. In typical jobs with overlap geometry, signals are obtained from the end of the geometry (root of the welding). 2. In such typical jobs, lack of side wall fusion, lack of fusion at root or geometrical indications can be distinguished ultrasonically 3. There is not lack of sidewall fusion or lack of fusion at weld exits to rejects such job. Correct interpretation is the key in such kind of jobs. REFERENCES 1. ASM Handbook Vol Alstom Technical Detail for P 91 Jobs