Welding Specification required

[The Expert]

Help/advice required please. We have a modification to carry out on some of our aircraft in the near future with the mods designed by our own in-house department as opposed to a mod from the aircraft manufacturer. Welding of structural components will be required that will almost certainly be manual TIG welding and will be typically 3 inch pipework flange and 3 inch butt-weld brackets. The final mod kit will be fabricated under EASA Part 21 subpart G, requiring to be released to service by an EASA Form 1.
I’m having difficulty determining what welding specification the welding should be carried out to, to meet EASA welding specifications, and I specifically need to determine the accept/reject criteria of welding defects found during NDT.
Many years ago when I worked in Cammell Laird shipyard heavy engineering (happy days), we welded to BS5500 for pressure vessels, and to BS 5135 for structural steel. What is the equivalent welding specification for aircraft structural parts?
:eek: Please don’t tell me to ask our design office – they don’t know and they don’t know they I know they don’t know!:ugh::confused:

[jxk]

Interesting question. You might try AC43-13 (the American aircraft maintenance/design/repair bible). Recently, I know Apex (formerly Robin) have suggested using this publication for reference. But guess what I've heard that EASA don't like AC43-13 and want to have their own equivalent.

[Salusa]

I don’t know the answer mate, but whatever you do don’t cock around with welding on aircraft.

The days of the individual approved welder have been replaced by specialist approved organisations.

I suggest you ask them.

And the fact your own design dept does not know the spec would also make me run a mile!

[NutLoose]

This is way way out of my comfort zone, I use a CAA approved welder who is ex a major Airline and still subcontracts for them, subject to his agreement I could Message you his number if that helps, though you just have Marshalls down the road and this is their bread and butter......

But as a possible help and point you in the right direction. this is from the FAA site, there will be an easa equivelent, probably a JAR with the same number.

from


Sec. 25.613

Material strength properties and design values.

(a) Material strength properties must be based on enough tests of material meeting approved specifications to establish design values on a statistical basis.
(b) Design values must be chosen so that the probability of any structure being understrength because of material variations is extremely remote.
(c) The effects of temperature on allowable stresses used for design in an essential component or structure must be considered where thermal effects are significant under normal operating conditions.
(d) The strength, detail design, and fabrication of the structure must minimize the probability of disastrous fatigue failure, particularly at points of stress concentration.
(e) Unless they are shown to be inapplicable in a particular case, the design values must be those contained in the following publications (obtainable from the Superintendent of Documents, Government Printing Office, Washington, D.C., 20402):

MIL-HDBK-5, "Metallic Materials and Elements for Flight Vehicle Structure";
MIL-HDBK-17, "Plastics for Flight Vehicles";
ANC-18, "Design of Wood Aircraft Structures"; and
MIL-HDBK-23, "Composite Construction for Flight Vehicles".

now the top book appears to have been superceeded by MMPDS-01 (FAA version of MIL-HDBK-5)

have a look at section 8.2

http://www2.tech.purdue.edu/at/courses/at308/Technical_Links/MMPDS/Chapter8.pdf

and 9

http://www2.tech.purdue.edu/at/courses/at308/Technical_Links/MMPDS/Chapter9.pdf

I found that to change from chapters i needed to alter the chapter number in the web address.


but again as reiterated this is just to point you in hopefully the right direction, the links above are on the web but there is no guarantee how up to date or accurate they are.. you really need to talk to people such as an approved welder , the CAA etc or an approved design organisation that can do this for you, even an approved NDT facility, again I could sort out a number for one for you for the latter.

[The Expert]

Many thanks to all above for their replies but I am no further forward!
There is a chicken and egg situation. I suspect that the approved welders don’t know either. On the job card for the part there is a box that has to be competed stating the welding specification. The welders usually state “As per customers requirement/specification” But the customer doesn’t know what to specify.
I suspect that there is a strong method of ‘we do it this way because we’ve always done it this way’ It is not raised during a QA audit because the QA people don’t know either! This is a can of worms.

Aviation welding in the UK and EASA is 25 years behind and is a cause for concern. The nearest UK standard that I can get my get my hands on is CAP 553 and CAP 554 BCARs section A and B chapter 8. This states specific details for welders test pieces and quotes DEF STAN 00-932 for tensile tests. Excellent! The old BS5500 for pressure vessels and BS5135 for structural steel quoted the exact amounts of porosity, slag inclusions, tungsten inclusions permissible. This was usually detected by NDT and a maximum size was specified either by a table or by arithmetic calculation. It also specified exactly what types of defects were not permissible in any shape size or form.
BCAR A/B chapter 8 states “specimens must show adequate penetrations and freedom from excess oxidation cracks, cavities, porosity, scale and slag. What does ‘adequate penetration’ mean? What does “freedom from” mean? Absolute zero? No defects of any kind at all?
It talks a lot and says bloody nothing! Furthermore, the old BCAR is now suspended and the EASA replacement has been in draft stage since October 2007 and is not yet issued! Unbelievable! There is no aviation welding standard.

[happybiker]

Re your modification.

One thing you also need to consider is that for installation on an EASA aircraft the design of the modification must be approved by an EASA Part 21 subpart J approved design organistion. Where the manufacture of parts that constitute the modification requires welding as part of the manufacturing process then the design organistion will need to include the specific welding process in its approved design data as part of the modification.

The Part 21 subpart G organistion that will manufacture the parts will need to use an approved welder for that part of the process. Information on the approval of welders in the UK is to be found in CAA BCARS Section A chapter A8-10. www.caa.co.uk/application.aspx?catid=33&pagetype=65&appid=11&mode=detail&id=220

[Nopax,thanx]

This may be a stoopid answer but as you're in Cambridge have you tried TWI?

http://www.twi.co.uk

[The Expert]

I haven't tried the Welding Institute, but I did single out individual people listed in the Aerospace Group, in the handbook of the British Institute of NDT - not one single reply! The Aerospace Group don't know either!
As time goes on I'm convonced that there is no national standard for aerospace.
TWI is a good idea. Thankyou! Will try tomorrow.

[Paradism]

I can give you an auditors viewpoint on this. I would, whilst auditing the 21G Org, ask the question "what processes have been specified for the welding and inspection of the parts?" Without that information, the parts cannot be manufactured as the 21G Org would be making themselves responsible in law for that part of the design, which they cannot legally do.

I would therefore suggest that the design data is incomplete and put the responsibility right back with the Part 21J DOA.

Having said that, there do appear to be a lot of references to ANSI/AWS D17.1:2001 Specification for Fusion Welding for Aerospace Applications, around the internet, that may be of some use. However, not being a welder or a designer, I cannot pass an expert opinion. Another avenue may be to ask the aircraft constructor which standard should be specified, especially if it affects aircraft primary or secondary structure. Of course, if it is manufacture of an accessory, the responsibility is totally that of the design organisation.

As far as my limited experience with standards is concerned, there are various British Standards for welding of different materials You could seek advise from the British Standards Institute direct, but it still comes down to the requirement that the standard should be specified by the design organisation.

I would caution also that welding, being a special process, may be outside of the Part 21G scope of approval that you hold, it's worth asking the question.

[The Expert]

Most helpful reply from Paradism (and everyone else) – many thanks.
I have been with my current organisation for only a year so I have inherited much of this. I had very little experience of Part 21 prior to this. Last first – welding is specified and approved within the scope of our Part 21, but specified only in broad and loose terms.
Your advice regarding placing the onus back onto the design department is spot on. The difficulty I face within my organisation is that our design department is an ivory tower collection of untouchable prima donnas - difficult but not insurmountable! Welding is contracted out to an outside agency with welders who hold CAA approval, but who state on the report that welding and inspection is carried out ‘as per customer requirements’ We’re going round in circles. :ugh:The welding agency do it this way ‘because they’ve always done it this way’ for us! :confused:
In my days in heavy engineering, every single weld technique was specified with its own detailed and individual procedure, stating welding rods, current setting, positive or negative earth, wall thickness of metal, type of metal, configuration (alignment) of parent materials – with sketch, whether it was a butt weld, fillet weld, full penetration, stitch weld etc etc, and also NDT techniques and specified what class of weld it is so that can be cross referred to a British Standard, or ASME 9 for accept/reject criteria for weld defects.
A weld procedure was usually a detailed full A4 page so for a large organisation, the weld procedures were a full voluminous manual in its own right being regularly updated. Quite a contrast. My gut feeling is that there should be probably at least three national aviation welding standards in the UK/EASA; a welding standard for structural parts, a slightly less critical standard for non-structural parts, and a welding standard for engine/hot parts/rotating parts, all specifying the techniques and accept/reject criteria.
I’m convinced that there is currently no national standard and this is a can of worms. I’ve spoken with the CAA surveyor – who is out of his depth and fobbed me off. I suspect that the CAA have not been asking the audit question that Paradism suggests above. :oh: If they did they would then know the answer and (hopefully) be prepared to pass on the advice! Oh dear! :=
On the plus side with this interesting exercise – I’m seriously considering writing a paper on it and using it to apply for CEng! :8 :ok: