This article discusses a proposal for a change under NB-2420 of Section III NB of ASME BPVC.
A. Introduction
The line 9 of last paragraph of NB-2420 of BPVC Section III NB says that use of controlled chemical composition is only permitted for carbon steel and low alloy steel consumables. This rule poses significant difficulty in implementation, especially in fabrication of covered electrodes of non-CS and non-LAS composition. This article explores the following aspects of this rule:
- What does the rule say in 2023 edition?
- What difficulties does this rule pose in industry?
- Deliberations done on the subject in BPV III SG MFE committee in the past three years.
- What did the earlier editions of Section III NB say on the subject?
- What do the other international codes say on the subject?
- Case for revision in code.
- Proposed code changes to para NB-2420.
B. What Does the Rule Say in 2023 Edition?
Line 9 in the last paragraph under NB-2420 states that ‘use of controlled chemical composition is permitted only for carbon and low alloy steel consumables.
Note: The term ‘the rule’ in all subsequent paragraphs of this article refers to this stipulation.
This means that only one wet mix of covering ingredients and one heat of core wire can be permitted in the manufacture of one lot of non-CS and non-LAS electrodes (e.g. stainless steel covered electrodes, nickel alloy covered electrodes, etc.).
This rule was introduced in its’ current form in 2017 edition of Section III NB for the first time, and has remained unchanged in this regard in all subsequent editions.
The last para of NB-2420 begins with the line that ‘when filler metal of controlled chemical composition (as opposed to heat control) is used, each container shall be identified…’ etc. etc. The phrase ‘as opposed to heat control’ here gives an indication that the discussion is about consumables that are identified by heat number, as opposed to those identified by dry mix/ wet mix numbers etc. This points towards bare rods/ wires that are used with OFW/SAW/GTAW/PAW/GMAW/EGW processes and the core wire of SMAW electrodes.
It is presumed that the line 9 under NB-2420, which states that ‘the use of chemical composition is only permitted for carbon and low alloy steel consumables’, is not to be read in isolation; and is in fact applicable only to the bunch of consumables referred to by the opening statement of the paragraph.
The language used in the earlier editions of code gives credence to this thinking, as further explained in para ‘E’ below.
The above discussion gives an impression that the said rule is not applicable to covering flux of SMAW electrodes. However, multiple interpretations – as explained in detail in para ‘D’ below, unequivocally convey that the rule is in fact applicable to covering flux of SMAW electrodes also.
Thus, a supplier of non-CS and non-LAS electrodes (such as SS & Ni-alloy electrodes) is constrained to use only one wet mix in the manufacture of a lot of electrodes.
C. Difficulties in Implementation in Industry
This section describes how SMAW electrodes are generally manufactured, and how the above-discussed rule poses a difficulty in manufacture of non-CS & non-LAS electrodes.
C.1. In Brief – How Covered Electrodes Are Manufactured
Covered electrodes are generally manufactured by the following process:
- Prepare dry mix by mixing together dry constituent powders in an appropriate proportion (this formulation is typically a trade secret of electrode manufacturer). Dry mix is the name given to the quantity that is mixed in a vessel in one go. Typically, dry mix capacity of most suppliers varies between 500 – 700 kg. Number of dry mixes used depends on the total order quantity needing to be made.
- Divide dry mix(es) into smaller parts called wet mixes. The term wet mix is the name given to the combination of liquid binder and the portion of dry mix mixed in a vessel in one go. Typically, wet mix capacity of most suppliers varies between 100 kg – 200 kg.
- Feed wet mix and bare cut lengths of core wire in an extrusion machine, which ejects finished electrodes on the other side.
NB-2420 requires all covered electrodes (used with SMAW process) to be of lot class C3. In the matter of covering flux, the C3 requirement (defined under SFA-5.01 of Section II-part C) entails using one wet mix only; alternatively, several wet mixes can be used – provided all are of controlled chemical composition. This phrase – controlled chemical composition – requires that chemistry checks should be done on all wet mixes to assure that all within a lot are equivalent. If the composition of all wet mixes is equivalent (i.e. the chemical composition is controlled), then the total collective electrode quantity produced from all wet mixes can be designated as a single lot.
Use of multiple wet mixes permits suppliers to accommodate large quantity under a lot. Considering that NB-2400 requires lot qualification of each lot, doing this reduces the volume of testing that the supplier is required to do.
C.2 How Is Controlled Chemical Composition Useful?
The allowance of controlled chemical composition is a useful tool to avoid large volume of unnecessary testing, while also assuring homogeneity in properties across the entire lot of electrodes. If the composition of all wet mixes falls within a range (this range is laid down by the supplier himself), then the resulting electrodes from all wet mixes would also have homogeneity in properties. Thus goes the intent behind this liberty.
C.3 Nature of The Problem at Hand
Most suppliers have a wet mix capacity not exceeding 200 kg. Flux forms around 30-35% of the total electrode weight. Thus, one wet mix results in finished electrodes of about 600 kg.
If only one wet mix is permitted in a lot of non-CS and non-LAS electrodes, the typical lot size gets restricted to about 600 kg. In other words, the required testing would need to be done for each 600 kg of electrodes.
A fabricator who procures 30 tons of electrode would need to do the required testing 50 times! This is an inordinately excess amount of testing. For Ni/Cu/Cu alloys, 50 batch tests under an inspection agency, and involving an accredited lab – becomes an economically prohibitive exercise, not to mention time, resources, and effort, without addition of significant value to the outcome.
D. Interpretations On The Subject
A number of interpretation requests have been asked from ASME on this subject. A few are reproduced below.
D.1. Interpretation request 21-1772, 22-1718
Background info:
The last paragraph of NB 2420 begins by saying “…when filler metal of controlled chemical composition (as opposed to heat control) is used…”. The paragraph goes on to say that “use of controlled chemical composition is only permitted for carbon and low alloy steel consumables.” The words “as opposed to heat control” at the beginning of the paragraph seem to indicate that this restriction on use of controlled chemical composition for only CS & LAS consumables is applicable only to consumables used with processes such as SAW, GTAW, PAW, GMAW etc.
Question 1: Does NB-2420 permit the use of controlled chemical composition for core wire of a nickel alloy electrode of Lot Class C3?
Reply 1: No.
Question 2: Does NB-2420 permit the use of controlled chemical composition for covering flux of a nickel alloy electrode of Lot Class C3?
Reply 2: No.
This interpretation was discussed at length in the MF&E subgroup virtual meeting too, on August, 09, 2023. The discussion in the meeting indicated that in the opinion of the MF&E subgroup – the rule is in fact applicable to covering flux of nickel alloy covered electrodes.
D.2. Interpretation request 23-2629
Question: Does NB-2420 permit the use of controlled chemical composition for lot classification C3 (Covered electrodes) & S2 (Fully metallic welding consumables) of Stainless Steel welding consumables?
Reply: No.
D.3. Interpretation request 23-2663
Background info:
As per last para of NB-2420: “In all cases, when filler metal of controlled chemical composition (as opposed to heat control) is used, each container of welding consumable shall be coded for identification and shall be traceable to the production period, the shift, the manufacturing line, and the analysis of the steel rod or strip. Carbon, manganese, silicon, and other intentionally added elements shall be identified to ensure that the material conforms to the SFA or user’s material specification. The use of controlled chemical composition is only permitted for carbon and low alloy steel consumables. Tests performed on welding material in the qualification of weld procedures will satisfy the testing requirements for the lot, heat, or combination of heat and batch of welding material used, provided the tests required by Article NB-4000 and this sub-article are made and the results conform to the requirements of this Article.”
This para talks about Carbon & Low alloy steel and do not provide clarity on other materials like Stainless Steel with regard to the use of controlled chemical composition during manufacture of welding consumables.
Question: Does NB-2420 permit use of a chemically controlled weld consumable that is not carbon or low alloy steel?
Reply: No.
Conclusion: All the above interpretation requests have elicited the response from Section III committee that the use of controlled chemical composition is in fact not permitted for non-CS and non-LAS consumables.
E. What Did the Earlier Editions Say?
While there is no exact equivalent of the rule in any of the editions dated 2015 and before, the clauses that come closest to the rule are NB-2420(e), (f). The clauses are reproduced below:
Extract from NB-2420 of Section III NB, 2015 edition…
‘(e) A heat of bare electrode, rod, wire, or consumable insert is defined as the material produced from the same melt of metal.
(f) Alternatively, for carbon and low alloy steel bare electrode, rod, wire, or consumable inserts for use with SAW, OFW, GMAW, GTAW, PAW, and EGW processes, a heat may be defined as either the material produced from the same melt of metal or the material produced from one type and size of wire when produced in a continuous period [not to exceed 24 hr and not to exceed 100,000 lb (45,000 kg)] from chemically controlled wire, subject to requirements of (1), (2), and (3) below.
(1) For the chemical control of the product of the rod mill, coils shall be limited to a maximum of one splice prior to processing the wire. Chemical analysis shall be made from a sample taken from both ends of each coil of mill-coiled rod furnished by mills permitting spliced coil practice of one splice maximum per coil. A chemical analysis need be taken from only one end of rod coils furnished by mills prohibiting spliced coil practice.
….’
Following can be reasonably inferred from the above paragraphs:
- Clauses NB-2420(e), (f) almost mirror the definition of heat and the alternative: controlled chemical composition for fully metallic consumables, given at para 3.4 and 3.5.2, respectively, in SFA-5.01 of ASME Section II Part C.
- Clause NB-2420(f) permits use of controlled chemical composition (as an alternative to the definition of heat in point NB-2420(e)), but only for consumables of CS and LAS composition. So for example, if an electrode supplier wants to make a lot of Ni-alloy or SS bare electrodes, rods or consumables inserts (to be used with SAW, GMAW, SAW, OFW, and EGW processes) using multiple heats of controlled chemical composition, he would not be permitted to do it, since NB-2420(f) permits controlled chemical composition (as an alternative to a single heat) for only CS and LAS consumables. Likewise, if he wants to manufacture Ni-alloy or SS covered electrodes and wants to use multiple heats of controlled chemical composition as the core wire, he would not be permitted to do it because of the aforementioned proscription in NB-2420(f).
- Although NB-2420(f) does not mention SMAW process, it can be reasonably inferred that the restriction on controlled chemical composition is applicable to the core wire of covered electrodes too, since the principle behind the restriction remains same.
- Clause NB-2420(f) has nothing to do with flux. That is, the covering flux applied on covered electrodes is not subject to the restriction on controlled chemical composition. In other words, multiple wet mixes (rather than a single wet mix) can be used, as expressly permitted in the definition of lot class C3 electrodes, even for non-CS and non-LAS electrodes.
Conclusion on earlier editions: All editions of Section III NB dated 2015 and before, permit use of multiple wet mixes (in other words, controlled chemical composition is allowed) in the manufacture of not just CS & LAS electrodes, but also for non-CS and non-LAS electrodes such as ENiCrFe3, E309-15 electrodes, etc.
The 2017 edition of Section III NB saw an overhaul of NB-2420, through which the erstwhile definitions of welding consumable related entities (such as dry mix, wet mix, heat, etc.) were replaced with a reference to their equivalent definitions in SFA-5.01 of Section II Part C.
F. What Do the Other International Codes Say?
If only wet mix is allowed in the manufacture of one lot of non-CS and non-LAS electrodes, it would entail batch testing of every 600 kg of electrodes. Do other codes require this volume of testing?
F.1. KTA Code
The relevant German Nuclear Safety Standards for nuclear power plants, i.e. KTA 1408.1, 1408.2, 1408.3 which pertain to welding consumables require mechanical testing of every 5000 kg of electrodes. Refer Table 5-1 of KTA-1408.2, 2017 edition.
F.2. ISO Codes
Most ISO codes point to ISO-14344 in matters of electrode procurement and testing. The ISO-14344 contains mostly the same requirements as contained in SFA-5.01 of Section II Part C.
F.3. RCC-M Code
RCC-M code, Section IV, para S2430 requires that SMAW electrodes shall be of lot class C3 as defined in ISO-14344, shall be of same trade name, and shall have a core wire from one heat only. The requirement that the core wire shall be of one heat here – is regardless of the whether electrode is CS, LAS, non-CS, or non-LAS. It is also notable that no additional requirement regarding the covering flux needing to be from a single wet mix is specified.
G. Case for Revision in Code
A number of factors justify the case for revision in NB-2420 with regard to the above-discussed rule. A few of them are as follows.
G.1. Changes Done in 2017 Edition Only Intended Replacing the Definitions, Not The Intent
The 2017 edition of Section III NB witnessed an overhaul of NB-2420. This overhaul introduced ‘lot classes’ (such as C3 for covered electrodes, S2 for bare rods/ wires, etc.) of consumables under NB-2420 for the first time. Lot classes are defined under SFA-5.01 of Section II Part C. This perhaps eased the burden of including detailed requirements under NB-2420, and instead accomplish the objective by simply specifying the lot class for various categories of consumables.
The overall intent of these changes was to replace the existing lot definitions for welding consumables with SFA-5.01 definitions. The erstwhile definitions (such as dry mix, wet mix, etc.) related to consumables were mostly equivalent to the corresponding definitions given in SFA-5.01 for these items and hence the changes made sense.
This indicates that NB-2420 did not witness any change in the intent regarding controlled chemical composition for non-CS and non-LAS consumables in 2017, and that the changes done were for the sake of convenience and uniformity between Section III NB and Section II Part C.
G.2. Code’s Restriction is Meant for Heat, Not Flux
Generally, a heat is defined as the material obtained from one furnace melt.
However, in cases where significant slag-metal reactions do not occur, an uninterrupted series of melts from the same set of source materials under same melting conditions can also be designated as a single heat, provided chemical composition of each melt stays within a controlled range. This amounts to controlled chemical composition, that is – use of multiple melts is permitted provided composition of all melts stays within a range established by the consumable supplier.
However, in cases where significant slag-metal reactions do occur (say, in melts involving reactive metals such as Al, Cu, Ni, Ti, Zi, etc.), such liberty cannot be permitted since one melt might be significantly different in composition from another, due to chemical reactions occurring during melting. For such cases, only the material obtained from one melt is allowed to designated as one heat.
This understanding, existing in Section II Part C since time immemorial, seems to be the reason behind the restriction imposed by NB-2420(f) (in editions older than 2017) regarding the use of controlled chemical composition for non-CS and non-LAS consumables.
Clearly, this restriction is intended only for metallic consumables (such as rods, wires, inserts to be used with OFW, GTAW, GMAW, SAW, EGW, etc.), and has no relation to fluxes of any kind. Therefore, the contentious rule introduced in 2017 edition, as described in para B above, & which continues to present day, and which has been attested to by Section III committee over multiple interpretations, is the result of NB-2420(f) not being transferred faithfully from the 2015 edition to the 2017 edition. The rule is therefore incorrectly understood.
G.3. Excessively and Unreasonably Stringent
The above discussion explains that if only wet mix is allowed in the manufacture of one lot of lot class C3 electrodes of non-CS & non-LAS type, the total quantity in one such lot gets restricted to 500 kg – 600 kg [this number may go up slightly for big consumable suppliers such as Lincoln electric, Bohler, etc., who may have large wet mix capacities]. Since each lot is required to be subjected to the requisite testing, the amount of testing that a fabricator who procures 30 tons needs to do – is extremely high.
Other equivalent international codes do not specify this kind of voluminous testing. ASME Section III NB, thus, is excessively and unreasonably stringent in this regard. A Code change is therefore, suggested.
G.4. Process of Manufacture of Non-CS & Non-LAS Electrodes is No Different From CS & LAS Electrodes
The process involved in the manufacture of covered electrodes, as described in para C.1, stays same for CS/LAS electrodes and Ni/Cu/Al etc. electrodes. Having multiple wet mixes, of controlled chemical composition, assures that the mechanical properties across the entire lot quantity made from multiple wet mixes would be uniform.
Treating electrodes made from different wet mixes as different lots adds no significant value to the electrode qualification exercise.
H. Proposed Change in NB-2420
The last paragraph under NB-2420 is shown below. The proposed change in indicated in red:
‘In all cases, when filler metal of controlled chemical composition (as opposed to heat control) is used, each container of welding consumable shall be coded for identification and shall be traceable to the production period, the shift, the manufacturing line, and the analysis of the steel rod or strip. Carbon, manganese, silicon, and other intentionally added elements shall be identified to ensure that the material conforms to the SFA or user’s material specification. The use of controlled chemical composition, as an alternate to a single heat, is only permitted for carbon and low alloy steel consumables. Tests performed on welding material in the qualification of weld procedures will satisfy the testing requirements for the lot, heat, or combination of heat and batch of welding material used, provided the tests required by Article NB-4000 and this subarticle are made and the results conform to the requirements of this Article.’
This was all on this subject. Please do oblige with your thoughts, observations, etc. Thanks for reading the lengthy post.