Q: Is it possible to produce remanufactured cast valve bodies that comply with NACE MR0175/ISO 15156 and NACE MR0103?
A: For most common cast materials, the simple answer to this question is “No,” but that answer deserves explanation. Let’s start by comparing the legacy NACE standard MR0175 version 2002 (and previous versions) with the current version (NACE MR0175/ISO 15156) and NACE MR0103.
NACE MR0175-2002 contained little control for welding. The general requirements were specified as follows:
“5.3.1 Welding procedures shall be used to produce weldments that comply with the hardness requirements specified for the base metal in Sections 3 and 4. Welding procedures shall be qualified according to AWS, API, ASME, or other appropriate industry codes. Welders using this procedure shall be familiar with the procedure and shall be capable of making welds that comply with the procedure.” 1
The paragraph specifically covering welding of carbon steels indicated:
“220.127.116.11 Welding procedure qualifications on carbon steels that use controls other than thermal stress relieving to control the hardness of the weldment shall also include a hardness traverse across the weld, HAZ, and base metal to ensure that the procedure is capable of producing a hardness of 22 HRC maximum in the condition in which it is used.” 1
Note that this paragraph provided no details with regard to the “controls other than thermal stress relieving,” and also didn’t define the “hardness traverse.” Although not stated directly, it also implied that such testing was not required when stress relieving was performed. For the most part, equipment producers used stress relieving to bring weld repairs in castings into compliance. Note that no specific stress-relieving requirements such as temperature, soak time or heating/cooling rates were specified, and no qualification testing (such as a hardness traverse) was required.
The paragraph for low-alloy steels and martensitic stainless steels indicated:
“18.104.22.168 Low-alloy steel and martensitic stainless steel weldments shall be stress relieved at a minimum temperature of 620°C (1150°F) to produce a hardness of 22 HRC maximum.” 1
Again, no stipulation was made that qualification testing was required.
There was also a requirement that filler materials for carbon steel and low-alloy steels could not contain more than 1% nickel.
For other materials, no specific requirements were stated.
Based upon these requirements, the prevailing practices for complying with NACE MR0175-2002 were to:
- Stress relieve carbon steel, alloy steel and martensitic stainless-steel castings, all of which are quench-hardenable.
- Use austenitic and duplex stainless-steel castings and nickel alloy castings in the as-welded condition, because these materials are not quench-hardenable.
NACE MR0175/ISO 15156 and NACE MR0103 both include requirements for welding procedure qualification that are much more specific and much more rigorous than those in NACE MR0175-2002.
NACE MR0175/ISO 15156 requires performing a weld procedure qualification (WPQ) hardness survey with either Vickers using a 10 kilogram load or with the Rockwell 15N scale for any material that has a maximum specified hardness limit. This encompasses the carbon steels, low-alloy steels, martensitic stainless steels, austenitic stainless steels and all the precipitation-hardenable alloys. For duplex stainless steels, a hardness survey is not required, but metallographic ferrite measurements are required in the weld deposit, and a microstructural examination at 400X is required to verify second-phase precipitates do not exist above certain levels.
NACE MR0103 requires that a WPQ hardness survey be performed with Vickers using a 10 kilogram load for carbon steels, alloy steels, martensitic stainless steels, duplex stainless steels and all of the precipitation-hardenable alloys. In addition, for duplex stainless steels, metallographic ferrite measurements are required in the weld deposit and heat-affected zone. Note that NACE MR0103 does not require a hardness survey for austenitic stainless steels.
Neither NACE MR0175/ISO 15156 nor NACE MR0103 require any special welding controls for the annealed solid solution nickel alloys.
That brings us back to the original question. Is there a way to ensure compliance with NACE MR0175/ISO 15156 and NACE MR0103 when remanufacturing a valve body casting?
The reason the answer to that is generally “no” is that welding can be performed on a cast valve body at many stages in its lifetime, by:
- the original foundry
- a third-party machine shop machining the casting
- the original valve manufacturer
- the customer
- the original valve manufacturer’s service organization or
- the customer’s third-party maintenance contractor.
Since the remanufacturer doesn’t know the entire history of the casting, it is impossible to certify that welding occurring on the casting has been performed using a welding procedure qualified in accordance with either of these NACE standards. It may have been welded with an improper filler, or using a process that requires special evaluation, such as production weld deposit hardness testing. (This is required when certain welding processes or filler materials are used to weld carbon steel in accordance with NACE MR0103.) Unlike NACE MR0175-2002 and previous versions, stress relieving is not viewed as an after-the-fact fix-all and is not adequate to upgrade the casting to be compliant with either NACE MR0175/ISO 15156 nor NACE MR0103.
The exception is the annealed solid solution nickel alloy castings acceptable per these NACE standards. Since these materials are acceptable with no welding controls, they can be certified compliant with NACE MR0175/ISO 15156 and NACE MR0103.
1. NACE Standard MR0175-2002, “Sulfide Stress Cracking Resistance Metallic Materials for Oilfield Equipment” (Houston, TX: NACE)