The Canadian CRN registration system requires that all fittings used on a vessel or included in a registered piping system carry CRNs. To register the fittings, design validation based either or code calculations, finite element analysis or proof testing is required.
When a design is based on code listed materials, the code of construction provides allowable operating stress levels. If the design of the pressure containing item is simple, the regular code rules can be used and will supply a pass/fail judgement. If no code rules exist for a complex or unusual shapes, Finite Element Analysis (FEA) can provide the stresses which can be compared with the listed allowables for a pass/fail judgement.
An alternate to code calculations is to proof test the item at stress levels far above operating. The items actual and guaranteed minimum tensile strengths are required for the proof test. The formula used is from VIII-1 UG-101(m):
Where B is the burst test pressure and P the allowed operating pressure. The burst test has to be at least 4 times the operating pressure. E is the welding efficiency if the item is welded - typically between 0.7 and 1.0. Two more pieces of information are required - Su - the specified minimum tensile strength of the material and Suavg - the tensile test results from the item under test. Typical proof test pressures are 5-6x operating pressure, a requirement far more conservative than regular code calculations or FEA.
For code listed materials, all of the required information is available for either calculations/FEA or for burst testing.
Codes B31.1 and B31.3 are useful for registering fittings because they allow unlisted materials to be adopted and because they provide fewer restrictive design rules. Be aware that ABSA has a new unpublished ruling that requires items that look like vessels (even slightly) to be registered under VIII-1 where adoption is not permitted. So far other provinces are not in agreement.
An unlisted material made to a specification can be adopted if the material's guaranteed minimum yield and tensile strength are available. The code adopted strength is based on a formula using these two inputs resulting in allowable design strength. Or the minimum tensile strength can be used in the proof test. Using this process, almost any IID listed material can be adopted for use in B31.1 or B31.3.
This is a typical formula for adopting unlisted material in B31.3. Sy and St are the materials guaranteed minimum strength. More complex methods are used at higher temperatures where the materials creep properties need to be taken into account. Availability of elevated temperature material properties can severely limit the adoptability of unlisted materials. Caution: see Unlisted Material Registration Problems below.
Many common fittings materials are not code listed and have no guaranteed minimum tensile or yield strength information. Two common examples: SAE1010 is a carbon steel and B85 A380 is a die cast aluminum. Both are made to chemical only specifications.
To use either of these materials in Canadian registered fittings, the purchaser has to agree with the mill/foundry what minimum tensile and yield strength level is acceptable. A specification referenced or written into each material batch purchase order is required. Chosen strength levels are obviously important. Set too high and excessive batches will be rejected upon physical testing. Set to low and the parts will not pass code calculations. Also note that the ratio between the actual and minimum tensile strength impacts the required burst test pressure. The lower the minimum specified strength, the higher the required proof test. A sample purchase order or a copy of the specification would be required with the CRN application. Caution: see Unlisted Material Registration Problems below.
If all of the above fails, most Canadian jurisdictions will allow a fitting to be registered with "unknown" materials if it can be proof tested to 10x operating pressure (no tensile strength testing required). This category includes many plastics that are not covered by the piping codes, glass, ceramics and steels that cannot be adopted by the above methods.
Clearly 10x operating is a severe test not possible with many otherwise safe products. This method is reserved for products that are highly overdesigned.
Update - Oct 2011. (PVE-4768)
The unlisted materials methods above were taught to us by jurisdictions for use with fittings, but they are not formally documented anywhere. They are a compromise between the desire to follow code rules which are designed for piping systems, not fittings and the acknowledgement that Canadian rules are unique, so if they are applied too tightly, few products produced internationally will be available for our use. The above methods are usually accepted but not always.
We recently had a job rejected by ABSA where we followed the unlisted material methods listed above for the registration of a valve made from 12L14 bar, a commonly used valve material. 12L14 is produced to several specifications, all which cover chemical but not physical specs. We were told that use of the material would not be allowed unless the manufacturer published a specification that covered the physical and chemical properties of 12L14, including all aspects listed in B31.3 323.1.2:
B31.3 2010 323.1.2 Unlisted Materials. Unlisted materials may be used provided they conform to a published specification covering chemistry, physical and mechanical properties, method and process of manufacture, heat treatment, and quality control, and otherwise meet the requirements of this Code. See also ASME BPV Code Section II, Part D, Appendix 5. Allowable stresses shall be determined in accordance with the applicable allowable stress basis of this Code or a more conservative basis.
The use of a published spec would follow the code rules of B31.3, the code of registration, but was an impossibility for the manufacturer so a product available internationally is not in use in Alberta. To date this has only affected one job. We do not know if all ABSA reviewers will agree to this new requirement.
