API 2017-08-18T14:04:22+00:00

W Maass (UK) Ltd – API Parts

W Maass UK are specialists in supplying API 6A and 17D flanges. These specifications can be daunting to fully understand if not totally familiar with them, so below are some pointers to help.

Many applications successfully use API flanges with non-compliant materials. Such example is ASTM A105 for a 5,000psi rated blind flange. This material’s strength is not high enough to comply with API 6A requirements, the material needs to have a yield strength greater than 60ksi and a UTS greater than 85ksi to be in accordance with API 6A.

Table 1 below shows typical materials that as standard are compliant with API 6A/17D requirements and those that are not. If using a material that’s not compliant then Customer should be aware and API max pressure rating is not guaranteed unless special design work has been performed to prove acceptable.

Type 2,000psi 3,000psi 5,0000psi 10,000psi
Weld Neck AISI 4130 60K

A694 F60

A182 F51 & F55

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

A694 F60

A182 F51 & F55

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

A694 F60

A182 F51 & F55

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A182 F316 & F304

Blind AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

Swivel NA NA AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

A182 F51 & F55

A694 F65

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

AISI 4140 75K

AISI 8630 75K

A182 F55

AISI 4130 60K

A694 F60

A694 F52

A350 LF2

A105

A182 F316 & F304

Table 1: API Complaint & Non-Compliant Materials (non-compliant are strikethrough)

API 6A uses a double letter system to categories material classes. These relate to the type of service the flange will encounter and the generic material type. Table 2 below shows API material class according to typical materials.

API 6A Class Sour Service
(NACE / ISO 15156)
Material Type Typical Grade
AA or BB* NO Carbon / Low Alloy Steel AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

CC NO Stainless Steel ASTM A182 F51 & F55
DD or EE** YES Carbon / Low Alloy Steel AISI 4130 60K

AISI 4140 75K

AISI 8630 75K

to NACE / ISO 15156

FF YES Stainless Steel ASTM A182 F51 & F55

to NACE / ISO 15156

HH*** YES Corrosion Resistant Alloy (CRA) ASTM B564 UNS N06625

to NACE / ISO 15156

Table 2 – API 6A Material Classes

* = For flange manufacture, doesn’t matter if AA or BB is selected as both have the same requirement.

** = For flange manufacture, doesn’t matter if DD or EE is selected as both have the same requirement.

*** = Fully clad flange is acceptable, e.g. CRA cladding on Carbon / Low Alloy Steel.

Many material grades don’t require impact testing as standard or test temperature and energy absorption requirements are different to API requirements. API 6A Temperature Classification is symbolised by a single letter which provides criteria for impact testing for flanges as per Table 3 below according to expected Operating Range.

Temperature Classification</strong Operating Temperature Range (°C)
MIN MAX
K -60 82
L -46 82
N -46 60
P -29 82
S -18 60
T -18 82
U -18 121
V 2 121

Table 3 – API 6A Temperature Range

API 6A / 17D flanges are never Raised Face type. They are always Ring Type Joints.

There can be some confusion over whether API flanges are the R type or BX type ring joint because the same flange can appear to have either option in some cases. Table 4 & Table 5 below summarises the ring joint type for API flanges.

Weld Neck and Blind Flanges to API 6A (Wellhead & Christmas Tree Equipment)
Size 2,000psi 3,000psi 5,000psi 10,000psi
1.13/16” R(2) R(2) R(2) BX
2.1/16” R R R BX
2.9/16” R R R BX
3.1/8” R R R BX
4.1/16” R R R BX
5.1/8” R R R BX
7.1/16” R R R BX
9” R R R BX
11” R R R BX
13.5/8” R R BX(1) BX
16.3/4” R R BX(1) BX
18.3/4” R(2) R(2) BX(2) BX(1)
21.1/16” R R BX(1) BX(1)
26.3/4” BX(1) BX(1) BX(2) BX(2)
30” BX(1) BX(1) BX(2) BX(2)

Table 4 – API 6A Ring Joint Type

  1.  Integral type flange modified to Weld Neck type by W Maaass UK Ltd.
  2.  Special design by W Maass UK Ltd.
Weld Neck and Swivel Flanges to API 17D
(Subsea Wellhead & Tree Equipment)
Size 5,000psi 10,000psi
2.1/16” BX BX
2.9/16” BX BX
3.1/8” BX BX
4.1/16” BX BX
5.1/8” BX BX
7.1/16” BX BX
9” BX BX
11” BX BX
13.5/8” BX BX

Table 5 – API 17D Ring Joint Type

*Note the different ring joint for 5,000psi ratings between API 6A and API 17D (up to 11”).

API 6A = R type

API 17D = BX type

After assembly, API flanges fitted with R type ring grooves stand off from each other. API Flanges fitted with BX type ring grooves meet face to face with no stand-off.

For API flanges fitted with R type ring grooves, Oval type or Octagonal type gaskets may be used.

For API flanges used subsea, gaskets must be drilled with a pressure release hole to prevent hydraulic locking and their name pre-fixed with an ‘S’, i.e. SR or SBX.

API 6A has four types of quality level for forging production and NDT testing. Each one has varying levels of inspection or material testing. Table 6 below provides a summary.

Special Requirement PSL 1 PSL 2 PSL 3 PSL 4
Mechanical Test Coupon (TC) (1) YES
Qualification Test Coupon (QTC)(1) YES YES YES
Tensile Test (according to Table 1) YES YES YES YES
Impact Test (according to Table 3) YES YES YES YES
Evidence of Hot Working Practice YES YES YES
Evidence of Melting Practice YES YES YES
Heat Sink & Contact Thermocouple YES
Quench Tank Temp Restrictions YES YES YES
Specific API Chemical Composition Limits YES YES YES
Cladding Chemical Composition Limits YES YES YES YES
Hardness Testing of Cladding (PQR) YES YES YES
Cladding Bend Test (PQR) YES YES YES YES
Cladding Thickness Check YES YES YES YES
Flange Hardness Testing YES YES YES
Dimensional Inspection YES YES YES YES
Traceability YES YES YES
Chemical Analysis (Product Analysis) YES YES YES
Visual Inspection (all surfaces) YES YES YES YES
MPI / Dye Pen Inspection Wetted Surfaces YES
MPI / Dye Pen Inspection All Surfaces YES YES
UT Inspection YES YES
MPI / Dye Pen Inspection prior to Cladding YES YES
MPI / Dye Pen Inspection of Cladding YES YES YES YES
UT Inspection of Cladding & Bond Test YES YES
Unique Item No. / Serialisation YES YES

Table 6 – Summary of PAI PSL Requirements

(1) – API 6A is very thorough with its requirements for where / how mechanical test samples are taken after forging production and heat treatment. It uses an Equivalent Round (ER) technique based on forging thickness in the as heat treated condition to ensure mechanical tests are representative of the parent forging. The size of the ER is important to achieving API compliance. A Test Coupon (TC) or Qualification Test Coupon (QTC) must be same heat and representative of the forgings it qualifies and be of no better quality (i.e. no higher reduction ratio or cleaner melt).

If you require any of our API products please contact us via Phone: 01744 453393, Email: sales@w-maass.co.uk  or click here for our contact us page.