Basic Weld Inspection
John Hoh
National Board
Category: Design/Fabrication
Summary: This article was originally published in the Winter 2010 National Board BULLETIN as the second of a two-part series. This is a continuation of the article Basic Weld Inspection - Part 1 originally published in the Fall 2009 edition of the BULLETIN, with more examples and tips the inspector can use as a guide. Some of the items in Part 2 may seem to be outside the realm of weld inspection but, when taken in context with the overall objective, they are relevant.
Note: The purpose of this article is to provide inspectors with a general knowledge of weld inspection. It is by no means intended to compare with the Certified Welding Inspector (CWI) requirements of the American Welding Society (AWS).
Part -1:
Weld inspection begins long before the first welding arc is struck. The inspector must review the job package to become familiar with the:
- welding processes to be used;
- materials and any special properties;
- joint configurations and preparation;
- welding procedure specifications to be used and any limitations;
- qualifications of welders to be used and any limitations;
- heat treatment (pre-heat or postweld), if any;
- nondestructive examination (NDE), if any; and
- specific ASME Code or NBIC requirements (for example, Section VIII, Div. 1, lethal service).
While not imperative, the inspector should learn to read common weld symbols such as the AWS symbols. At the very least, the inspector should always carry a reference guide to interpret weld symbols. Having reviewed all this information in advance, the inspector will be prepared to recognize any problems as they develop rather than after-the-fact.
The following examples and tips are practical applications the inspector can use as a guide.
1. The manufacturer or repair organization (certificate holder) has indicated on the job drawing that a weld joint is to be prepared with a 60-degree bevel and root gap of 1/16 inch. Unless the bevels are milled on precision machinery, it is doubtful they will achieve an exact 60-degree bevel as indicated. The easiest solution for the certificate holder is to allow a range of plus or minus a few degrees of the target value. The same holds true for a root gap dimension with no plus or minus tolerance. Even the best welder will have difficulty maintaining an exact root gap dimension. Providing a plus or minus tolerance will make the welder’s job much easier.
2. The inspector can use scraps of weld filler wire or rods as a gauge to quickly identify root gaps that are beyond the tolerance range. For example, if the target root gap is 3/32 inch plus or minus 1/32 inch, the inspector should be able to insert a 1/16-inch wire into the gap with little or no resistance. Likewise a 1/8-inch wire should exhibit no side-to-side movement across the gap. Real world situations are rarely this convenient, but the inspector can develop a sense of “too tight” or “too loose” with experience.
3. The certificate holder has designed a simple nozzle to be welded to a flat head (Fig. 1). The nozzle axis is 90° to the flat head, and the attachment weld includes a 3/8-inch fillet weld. The inspector can easily measure the fillet weld to ensure compliance. Now, let’s install the same nozzle in a small diameter vessel shell (Fig. 2). The fillet weld will tend to spread or flatten on opposite sides of the nozzle due to the curvature of the shell. The inspector will need to ensure that the certificate holder has deposited enough weld to meet the design criteria. This example becomes even more critical if the nozzle is installed at an angle other than 90° (Fig. 3).
4. Using the same nozzle attachment example as described above, let’s look at the weld joint preparation. The certificate holder has specified a 45-degree bevel around the circumference of the hole in the flat head and the vessel shell. Again, the flat head will be very easy to measure, since there is a single plane of reference (Fig. 4). The curved shell will present more of a challenge. The inspector will have to determine if the certificate holder is referencing the bevel from the vertical axis of the nozzle (Fig. 5) or from the variable reference plane of the curved shell (Fig. 6).
5. When bevels are prepared with a cutting torch and finished with a grinder, it is very difficult to maintain an exact angle. This is why allowing a plus or minus tolerance is so important. Even obtaining a perfectly circular hole when using a torch and grinder is difficult. Fixtures are available which attach to the torch to aid in cutting circular holes and bevels, but the setup is sometimes inconvenient.
6. A certificate holder is preparing to weld several hundred circumferential joints in power boiler tubes. ASME Section I requires these welds to be full penetration, but due to the diameter, thickness, and location in the boiler, radiography of the welds is not required (PW-41, Table PW-11). How does the inspector ensure compliance with the code? Inspectors are trained to believe only what their eyes tell them; but when the inspector cannot see the inner surface of the tube, it becomes difficult to accept that situation. This is when the inspector must take what some would call a “leap of faith.” If the tube ends are properly prepared (beveled) and a qualified welder is using a qualified welding procedure, the odds are very good that the welds will be full penetration. Does this mean the inspector should just accept all this at face value and walk away? Absolutely not! If the inspector is unfamiliar with this certificate holder’s welding procedures and welders, the inspector has the right – and duty – to witness a few of the welds being made to ensure code compliance. One “red flag” to a potential problem would be if the inspector observes that the tube ends have not been beveled. The inspector should immediately ask the certificate holder about this situation. It could be as simple as the certificate holder having just not performed that step in the process yet, or it could be as bad as his or her having tried to save time and money by not beveling the ends. From a practical standpoint, it is extremely difficult, if not impossible, to obtain a full penetration weld when the tube ends are not beveled. The welder would need to start with a large root gap and then be very careful not to “push through” excess filler metal to cause weld build-up on the inside of the tube.
Part -2:
7. A pressure vessel manufacturer is manufacturing a lethal service vessel. ASME Section VIII, Div. 1, paragraph UW-2 (a)(1)(d) states that all Category D joints shall be full penetration welds. That means the weld metal must extend completely from one face of the joint to the opposing face of the joint. Without watching the entire welding process, how does the inspector ensure the manufacturer has complied with Code requirements? A review of the welding procedure and any supplementary instructions combined with a verification of the joint preparation will tell the inspector much of the story. If the full penetration weld is to be accomplished by welding from both sides, the inspector should make a point of observing how the root of the first weld is prepared for incorporating the weld on the opposing face. This is usually done by mechanical means (such as grinding or chipping) or thermal gouging.
8. When welding in areas with limited access to move, welders will sometimes shorten SMAW welding rods and GTAW filler wire. To shorten the SMAW rod, the welder will grip the rod in the electrode holder a few inches from the bare end and crumble the flux until he or she is able to grip a bare portion of the rod. When this is done, the rod identification is usually destroyed since it is normally printed on the flux close to the bare end. GTAW filler wire normally comes in 36-inch lengths with identification on one or both ends of the wire in the form of a flag-type label or embossing. A welder will seldom attempt to use a full length of wire because the free end may hit an obstruction or in some way impede the welder’s manipulation of the wire in the weld puddle. A welder may cut the length of filler wire in two or more pieces to make it easier to handle. Depending upon how the filler wire is marked, there could be one or more pieces without identification. If the certificate holder is using only one type and size of SMAW rod or GTAW wire (such as 3/32 in. E7018 or ER70S-6), the inspector may feel more comfortable if rods or wire with missing identification are found at the welder’s station. However, most certificate holders use more than one type and size of rod or wire, and the inspector must always ensure there are adequate controls in place to maintain rod or wire identification.
9. SMAW welding rod storage seems to always stir up a lively debate. The rod manufacturer’s recommendations should always be followed or, at the very least, the rods should be stored in compliance with the information found in ASME Section II, Part C. As an example, SFA-5.1, Annex 6.11 and SFA-5.5, Annex 6.12 discuss moisture content and conditioning for carbon steel and low-alloy steel electrodes (rods). One interesting point found in these references deals with rods such as E6010 with cellulosic coverings (flux). They actually need a moisture level of approximately 3 to 7 percent to operate properly. That means if these rods are stored in a heated oven, they may be too dry to use. I have personally seen E6010 rods taken from an oven, and the flux crumbles and falls off with the slightest touch. To the other extreme, I have seen a welder quickly dip an E6010 rod in a bucket of water immediately before striking an arc. This was on plate steel in a non-pressure boundary application so there were no ASME or NBIC violation concerns, but I am sure it exceeded the rod manufacturer’s recommended moisture content. This is definitely not condoned or recommended.
10. Holding ovens for welding rods are commercially available in many sizes. Human resourcefulness has also converted derelict refrigerators into makeshift holding ovens by installing light bulbs as the heat source. Is that permitted? As far as I know, it is not prohibited. The key, in my opinion, is the ability to achieve and maintain the recommended temperature. For example, SFA-5.1, Annex Table A3 shows a temperature range of 50°F – 250°F above ambient temperature for E7018 rods. It should not be difficult to obtain 50°F above ambient temperature during the winter in a shop where the temperature is 60°F. But, go to a shop in Louisiana or Florida in the summer, and the ambient temperature may easily be over 100°F. Can a simple light bulb in an old refrigerator achieve the necessary temperature in those conditions? There are variables such as the wattage and number of light bulbs in addition to how well the old refrigerator is insulated and sealed. As part of their normal monitoring duties, inspectors should be verifying the rod storage conditions no matter if a commercial oven is used or if a homemade alternative is in place.
11. While we are on the subject of welding rod storage, it seems that there are always a few people who mistake holding ovens with drying or rebaking. Looking at the table below, we find E7018 should be held or stored at 50°F – 250°F above ambient temperature. If the rod flux may have absorbed excess moisture, then it may be reconditioned by drying or rebaking. That requires a temperature of 500°F – 800°F for 1-2 hours for E7018. Looking at the specifications for one manufacturer of electrode ovens, their holding ovens are capable of 550°F plus or minus 25°. That would just barely meet the minimum rebaking temperature specified in Table A3. The same manufacturer offers another purpose-built oven capable of reaching 800°F. The two big differences in their construction are the electric heating elements and the insulation thickness.
As you can see, weld inspection includes much more than just looking at the finished product. The best advice for an inspector is to stop for a moment and think about every element which goes into making a weld. That can become the inspector’s checklist for review, inspection, and verification.
TABLE A3
Typical Storage and Drying Conditions for Covered Arc Welding Electrodes
| AWS Classification | Storage Conditions(1,2) | Drying Conditions(3) | ||
| A5.1 | A5.1M | Ambient Air | Holding Ovens | |
| E6010, E6011 | E4310, E4311 | Ambient temperature | Not recommended | Not recommended |
| E6012, E6013 | E4312, E4313 | 80ºF ± 20ºF | 20ºF to 40ºF | 275ºF ± 25ºF |
| E6018, E7015 | E4318, E4915 | Not recommended | 50ºF to 250ºF | 500ºF to 800ºF |
Notes:
(1) After removal from manufacturer's packaging.
(2) Some of these electrode classifications may be designated as meeting low moisture absorbing requirements.
(3) Because of inherent differences in covering composition, the manufacturers should be consulted for the exact drying conditions.
Table and Notes reprinted from ASME 2007 BPVC, Section II-Part C, by permission of the American Society of Mechanical Engineers. All rights reserved.
Source: http://www.nationalboard.org/
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