comparison of ISO 15614- 1 and ASME IX (iso 15614-1 vs asme ix)

WPS Qualification as per ASME Section IX, can I use same WPS according to ISO 15614-1? This is one of most frequently question, I heard from many welding engineers and Welding Inspectors.

Both the BPVC Section IX-Welding, Brazing, and Fusing Qualifications & ISO 15614-1:2017-Specification and qualification of welding procedures for metallic materials — Welding procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys are applicable for WPS-PQR qualification.

The one main difference is ASME Section IX is a Code while ISO 15614-1 is a standard, although both make users to comply the minimum specified requirements.

What ASME Section IX & ISO 15614-1 covers?

ASME IX covers the qualification of welders and welding operators, welding procedures, brazing operatives and brazing procedures for the complete range of ferrous and non-ferrous engineering metals (steels, copper, nickel, aluminium, titanium and zirconium alloys) and oxy-gas, arc, power beam, resistance and solid phase welding processes.

ISO 15614-1 covers the welding procedure qualification of arc and gas welds in steel and nickel alloys only. Other alloys and joining processes are covered by additional specifications within the ISO 15614 series. So, ISO 15614-1 is only limited to Welding procedure Specification (WPS) qualification while ASME cover procedure (WPS) and performance (WPQ) qualifications.

Welding Variables

Both specifications identify essential variable (although ISO 15614-1 does not describe them as such but only as essential variables) to each of which is assigned a range of approval. A change to an essential variable outside of its range of approval requires the welding procedure to be re-qualified.

ASME IX in addition identifies supplementary and non-essential variables. Supplementary variables are only applicable when toughness requirements are specified by the construction code, eg ASME VIII or ASME B31.3. Non-essential variables, as the name suggests, are those variables that are not regarded as affecting the quality or mechanical properties of the welded joint and comprise such variables as the weld preparation, shield gas flow rate, method of back gouging, shield gas nozzle size etc. Although these variables are non-essential it is a requirement that they should be referenced on the welding procedure. It is therefore NOT acceptable to use a butt welding procedure to specify how a fillet weld should be made.

ISO 15614-1 does not identify any variables as non-essential;  where a variable is not regarded as significant it is simply not referenced in the specification. There are several variables in both specifications where there is no range of approval;  the manufacturer, the welding process and the application or deletion of post weld heat treatment (PWHT) for example.

Material Grouping in ASME Section IX & ISO 15614-1

In order to reduce the amount of qualification testing, both specifications i.e. ASME & ISO group alloys of similar properties together. Qualifying the WPS with one material within the same group allows the other material within the group to be welded without need of re-qualification.

ASME IX assigns the P number & groups numbers (Given in table QW-422) for ferrous materials being numbered P1 to P15F. Any alloy that does not have a P number is considered as unassigned; a procedure qualification carried out using an unassigned material qualifies only that specific designation of material e.g. WPS qualification carried with AISI 4140, qualify procedure only for AISI 4140 material. in new editions of ASME Section IX & ISO 15608, to bring the harmonization between ASME & ISO some materials that complied with the ASME and/or ASTM material specifications and/or had a UNS number were assigned P numbers in ASME & group number in ISO 15608 (But only limited materials). However, a limited number of EN, Canadian, Chinese and Japanese alloys have now been introduced into the list of assigned alloys.

Note: details of material grouping which followed by ISO 15614-1 can be found in ISO 15608.

ISO 15614- 1 also groups steel and nickel alloys into families with similar properties but is somewhat less prescriptive than the ASME code in that, provided alloys have similar chemical compositions and mechanical properties, the material specification is not relevant – for example a plain carbon steel with less than 0.25%C and a minimum specified yield strength less than 460MPa  falls into Group 1 irrespective of whether or not it is a pressure vessel or structural steel or supplied in accordance with EN or ASTM material specifications. To determine into which group the alloy falls reference should be made to ISO/TR 15608, the specification that lists both ferrous and non-ferrous alloys and assigns them a group number.

Mechanical testing in ASME Section IX & ISO 15614-1

  • ASME IX requires only tensile and bend tests to qualify a butt weld. ISO 15614 Pt1 requires a far more extensive test program of visual inspection, radiography or ultrasonic examination, surface crack detection, tensile and bend tests and macro-examination. In certain circumstances Charpy-V impact tests and hardness surveys are also required. 
  • ASME IX specifies that the tensile strength of the cross joint tensile specimen shall be at least that of the minimum specified for the parent metal and that bend test coupons should have no discontinuity greater than 3mm. ISO 15614 Pt1 has identical requirements for these mechanical tests but in addition specifies an acceptance standard for the non-destructive testing; impact test results, when required, that match the parent material toughness and hardness limits when hardness testing is required.
  • ISO 15614-1 requires Charpy-V impact testing for steels over 12mm thick when the material specification requires it. ASME requires impact testing only when specified in the application standard. This requirement makes heat input a supplementary essential variable in ASME IX but an essential variable in ISO 15614-1.
  • Hardness testing is required by ISO 15614-1 for all ferritic steels with a specified minimum yield strength greater than 275MPa. A maximum hardness for joints in either the as-welded of PWHT condition is specified. ASME IX does not require hardness testing. 

Other differences

  • ASME IX allows a reduction in preheat of 55° C before requalification is required. ISO 15614-1 does not permit any reduction in preheat from that used in the qualification test.
  • ASME allows the maximum interpass temperature to be 55°C above that measured in the qualification test. ISO 15614- 1 permits no such increase.
  • ASME IX requires pressure containing fillet welds to be qualified by a butt weld procedure qualification test. Non-pressure retaining fillet welds may be qualified by a fillet weld test only. ISO 15614-1 requires a fillet weld to be qualified by a butt weld when mechanical properties “…. are relevant to the application…” i.e when it is a load carrying fillet weld. In addition, whilst a butt weld will qualify a fillet weld “….fillet weld tests shall be required where this is the predominant form of production welding…” i.e. an ISO compliant welding procedure where the majority of the welding is of load carrying fillet welds must reference both a butt weld and a fillet weld procedure qualification.
  • Weld metal transfer mode, where relevant, is an essential variable in both ISO 15614-1 and ASME IX but the current type is an essential variable in ISO 15614-1 and a supplementary essential variable in ASME IX.
  • A change from manual to automatic welding is an essential variable in ISO 15614-1 but a non-essential variable in ASME IX.

Whilst there are several other variables in the two specifications that have substantially different ranges of approval there are many that have ranges that are very similar – material thickness being but one example.

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