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Basic Weld Inspection - Part 2

Print Date: 12/11/2017 11:08:17 AM

John Hoh
Senior Staff Engineer
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: Items 1 through 6 were included in the article Basic Weld Inspection – Part 1.

  1. 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.
  1. 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.
  1. 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.
  1. 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.
  1. 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
E6019, E6020,
E6022, E6027,
E7014, E7024,
E7027
E4312, E4313
E4319, E4320,
E4322, E4327,
E4914, E4924,
E4927
80ºF ± 20ºF
[30ºC ± 10ºC]
50% max.
relative humidity
20ºF to 40ºF
[10ºC to 20ºC]
above ambient
temperature
275ºF ± 25ºF
[135ºC ± 15ºC]
1 hr at temperature
E6018, E7015
E7016, E7018,
E7028, E7018M,
E7048
E4318, E4915
E4916, E4918,
E4928, E4918M,
E4948
Not recommended 50ºF to 250ºF
[30ºC to 140ºC]
above ambient
temperature
500ºF to 800ºF
[260ºC to 425ºC]
1-2 hr at
temperature

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.