Eleven lines, three accreditation positions: reading an aerospace test list before the order

TCR Engineering's Mahape laboratory in Navi Mumbai holds NADCAP AC7101 Materials Testing accreditation (PRI certificate 29415245997) and NABL ISO/IEC 17025:2017 accreditation (NABLT0726MH18640). When an aerospace manufacturer in India sent an eleven-line test list asking for a NADCAP laboratory, the reply placed each line in one of three accreditation positions.

• The request: an independent, NADCAP-accredited materials testing laboratory, with an eleven-line test list.
• Inside the NADCAP AC7101 checklists: two lines, hardness (codes M1 Brinell and M2 Rockwell) and tensile testing (code A, room temperature tensile).
• Inside NABL ISO/IEC 17025 only: methods on certificate NABLT0726MH18640 that sit outside the NADCAP checklists, such as coating thickness by eddy current to ASTM E376.
• Inside neither: tests performed to the named standard and reported as standard laboratory testing, and one test not undertaken.
• Needed before quoting: the governing specification for three lines, a controlled copy of a prime's process specification, and a customer's in-house method.
• What TCR is not: a heat treater or a holder of any aerospace prime approval. It is the verification-testing partner.

A NADCAP laboratory does not make every result a NADCAP result

NADCAP accreditation is granted per audit checklist and per code, not to a building. An AC7101 laboratory carries the NADCAP symbol only on results produced under the codes on its scope. Everything else is reported under its ISO/IEC 17025 accreditation, where the method is on that scope, or as standard laboratory testing with no accreditation claimed.

TCR Engineering's scope, read off the PRI certificate, is:

With TCR Advanced at Vadodara holding its own certificate, TCR is the first Indian group with two NADCAP AC7101 laboratories. That answers only part of a buyer's question. Each line of a test list has its own accreditation position, and the buyer who reads them before the purchase order knows what the report will carry.

The eleven lines, one by one

The list as it arrived, anonymised, with the position each line took in TCR's reply. The NABL column is read against the certificate annexure.

The two lines inside NADCAP, and the specimen question

Hardness to ASTM E10 (Brinell) and ASTM E18 (Rockwell) maps directly onto codes M1 and M2, and both methods also sit on the NABL scope.

Tensile testing named five methods for one test. ASTM A370 is written for steel products, ASTM B557 for aluminium and magnesium alloy products, ASTM E8/E8M for metallic materials generally, ISO 6892 is the international metallic tensile method, and EN 2002-1 belongs to the European aerospace series. They differ in specimen geometry, extensometry and test speed control, so naming all five leaves the choice to the laboratory. The material specification normally names one, and the order should name that one. Four of the five are on the NABL scope; EN 2002-1 is not.

The line also said that specimen preparation was in the customer's scope. TCR's NADCAP scope includes code Z, standard specimen machining, in its own machine shop. When the laboratory machines the specimen, the coupon, the specimen and the result stay in one accredited chain. When the customer machines it, the laboratory checks dimensions, tests under code A, and the report records that the specimen was supplied machined. Machining damage then belongs to the specimen's supplier, not to the test. Either route is legitimate; the order should say which applies.

HTO, eutectic melting and clad diffusion: a handbook is not an acceptance criterion

Lines 3 and 4 asked for three metallographic checks that are made after aluminium alloys are solution heat treated, and all three are read on a polished and etched cross-section.

• High temperature oxidation (HTO): damage that moisture in the furnace atmosphere can cause during solution treatment, seen as blisters and voids at or near the surface.
• Eutectic melting: melting of low-melting constituents when the metal is overheated during solution treatment, seen as rosettes and resolidified films at grain boundaries.
• Alclad diffusion: on clad sheet, alloying elements from the core diffuse into the high-purity aluminium cladding during heating; the check measures how far, against the cladding thickness.

The method named for all three was ASM Handbook Volume 9. The handbook shows what these conditions look like. It does not say where to section, how many sections, which etchant and magnification, or what extent fails the part. Those come from the specification the heat treatment was done to, the buyer's or the prime's. Without it a laboratory can describe a microstructure but not give a verdict, which is why the reply asked the customer to elaborate.

The NABL scope carries micro examination of general structure to ASM Volume 9, and the NADCAP scope carries metallographic evaluation (L0). Which of them, if either, a given check reports under is settled once the governing specification is in hand. These checks belong to heat treatment verification: TCR examines the heat treater's samples and does not heat-treat.

When the list cites a prime's process specification

Line 6 named ASTM F2111 together with a prime's process specification. ASTM F2111 is a practice for measuring intergranular attack and end grain pitting on metals caused by aircraft chemical processes such as cleaners, strippers and etchants. By its own statement it does not supply every qualification parameter or the acceptance criteria; those come from the procurement, material or process specification, here the prime's document.

TCR holds no aerospace prime approval. A laboratory in that position can still test to a prime's specification, on request, provided four things hold:

1. The customer supplies a controlled copy of the specification, at the revision the order requires.
2. The test is run to that revision, and the report names the specification and revision.
3. The report states the accreditation position of the result, which for this line is standard laboratory testing.
4. No prime approval is claimed, implied or printed.

"IGA" also needs care. An intergranular attack depth read on a heat-treated cross-section is a metallographic measurement; ASTM F2111 is an exposure test of a chemical process on a metal. A test list should not leave the laboratory to guess which is meant.

Line 8 cited a prime's own test method for dry film thickness by eddy current. TCR proposed ASTM E376, which is on the NABL scope. Whether a published method may stand in for a prime's method is the buyer's decision, and the report names the method actually used.

Weld macro, corrosion and paint: performed, reported, or declined

Macro examination to AWS D17.1 (line 5), the specification for fusion welding of aerospace parts, is performed and reported as standard laboratory testing. Macro etch and macro examination sit on the NABL scope under ASTM E340, ASME Section IX and API 1104, but not under AWS D17.1.

Intergranular corrosion to ASTM G110 (line 7) immerses heat-treatable aluminium alloys, mainly 2xxx and 7xxx, in sodium chloride and hydrogen peroxide. The practice does not address sampling or interpretation, so acceptance again comes from the material or buyer specification. G110 is not on the NABL scope; the aluminium tests that are, the EXCO exfoliation corrosion test to ASTM G34 and the NAMLT intergranular corrosion test to ASTM G67, sit with stress corrosion cracking of aluminium alloys and corrosion testing.

Dry adhesion to ISO 2409 (line 9), the cross-cut test on paint, is performed as standard laboratory testing within coating evaluation. Wet adhesion to ISO 2812 with ISO 2808 (line 10) is not undertaken, and the reply said so before any order. Reticulation and solvent resistance (line 11) cited the customer's own method, which a laboratory cannot quote without reading, so the reply asked for it.

Dr. Ajay Essampally heads quality assurance at TCR Engineering and leads its NADCAP AC7101 Materials Testing accreditation.

What a test list should carry before the purchase order

A list that carries the following can be answered line by line in one reply:

1. One governing method per test, from the material or drawing specification.
2. The governing specification and its revision for every metallographic, corrosion or coating line where acceptance is not in the test method: the heat-treatment specification for HTO, eutectic melting and clad diffusion, the material specification for intergranular corrosion.
3. A controlled copy of any prime's process specification the line cites, with the revision, and a note of whether a published method may substitute.
4. The customer's in-house methods in full, where a line cites one.
5. Who machines the specimens, the customer or the laboratory under code Z, with the drawing for each specimen type.
6. The accreditation position required on each line: NADCAP, NABL, or standard laboratory testing accepted.
7. Alloy, temper and product form for each sample.

TCR's wider aerospace scope against both accreditations is on the aerospace industry page, the certificates on the quality and accreditation page, and the background in TCR's AC7101 accreditation at two laboratories and Make in India, Test in India.

This article was written and edited by the TCR Newsroom, the editorial desk of the TCR group, covering materials testing, inspection and asset integrity work across TCR’s laboratories in India and Saudi Arabia and its alliances in Qatar, Japan and beyond.